Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisAlleleFrequencyAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisAlleleFrequencyAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisAlleleFrequencyAnalyzer.cs	(revision 16337)
@@ -0,0 +1,117 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Analysis;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("SymbolicDataAnalysisAlleleFrequencyAnalyzer", "")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisAlleleFrequencyAnalyzer : AlleleFrequencyAnalyzer<ISymbolicExpressionTree>, ISymbolicDataAnalysisAnalyzer {
+    private const string AlleleTreeDepthParameterName = "AlleleTreeDepth";
+
+    #region parameter properties
+    public IScopeTreeLookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter {
+      get { return SolutionParameter; }
+    }
+
+    public ILookupParameter<Optimization.ResultCollection> ResultCollectionParameter {
+      get { return ResultsParameter; }
+    }
+
+    public IFixedValueParameter<IntValue> AlleleTreeDepthParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[AlleleTreeDepthParameterName]; }
+    }
+    #endregion
+    #region properties
+    public int AlleleTreeDepth {
+      get { return AlleleTreeDepthParameter.Value.Value; }
+      set { AlleleTreeDepthParameter.Value.Value = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisAlleleFrequencyAnalyzer(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisAlleleFrequencyAnalyzer(SymbolicDataAnalysisAlleleFrequencyAnalyzer original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisAlleleFrequencyAnalyzer()
+      : base() {
+      Parameters.Add(new FixedValueParameter<IntValue>(AlleleTreeDepthParameterName, "The depth of subtrees that should be considered as allele", new IntValue(2)));
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisAlleleFrequencyAnalyzer(this, cloner);
+    }
+
+    protected override Allele[] CalculateAlleles(ISymbolicExpressionTree solution) {
+      return CalculateAlleles(solution, AlleleTreeDepth);
+    }
+
+    public static Allele[] CalculateAlleles(ISymbolicExpressionTree solution, int alleleTreedepth) {
+      return GetAllSubtreesOfDepth(solution, alleleTreedepth)
+        .Select(t => GetAlleleFromSubtreeOfDepth(t, alleleTreedepth))
+        .ToArray();
+    }
+
+    private static Allele GetAlleleFromSubtreeOfDepth(ISymbolicExpressionTreeNode tree, int d) {
+      string textualRepresentation = GetTextualRepresentationFromSubtreeOfDepth(tree, d);
+      return new Allele(textualRepresentation);
+    }
+
+    private static string GetTextualRepresentationFromSubtreeOfDepth(ISymbolicExpressionTreeNode tree, int d) {
+      if (d == 0) return "";
+      StringBuilder builder = new StringBuilder();
+      var varTreeNode = tree as VariableTreeNode;
+      var constTreeNode = tree as ConstantTreeNode;
+      var factorVarTreeNode = tree as FactorVariableTreeNode;
+      var binFactorVarTreeNode = tree as BinaryFactorVariableTreeNode;
+      if (varTreeNode != null) {
+        builder.Append("(var " + varTreeNode.VariableName);
+      } else if (factorVarTreeNode != null) {
+        builder.Append("(factor " + factorVarTreeNode.VariableName);
+      } else if (binFactorVarTreeNode != null) {
+        builder.Append("(factor " + binFactorVarTreeNode.VariableName + "=" + binFactorVarTreeNode.VariableValue);
+      } else if (constTreeNode != null) {
+        builder.Append("(const");
+      } else {
+        builder.Append("(" + tree.ToString());
+      }
+      for (int i = 0; i < tree.SubtreeCount; i++) {
+        builder.Append(" " + GetTextualRepresentationFromSubtreeOfDepth(tree.GetSubtree(i), d - 1));
+      }
+      builder.Append(")");
+      return builder.ToString();
+    }
+
+    private static IEnumerable<ISymbolicExpressionTreeNode> GetAllSubtreesOfDepth(ISymbolicExpressionTree solution, int d) {
+      return from node in solution.IterateNodesPostfix()
+             where node.GetDepth() >= d
+             select node;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisAnalyzer.cs	(revision 16337)
@@ -0,0 +1,69 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Operators;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Abstract base class for symbolic data analysis analyzers.
+  /// </summary>
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisAnalyzer : SingleSuccessorOperator, ISymbolicDataAnalysisAnalyzer {
+    private const string SymbolicExpressionTreeParameterName = "SymbolicExpressionTree";
+    private const string ResultCollectionParameterName = "Results";
+
+    #region parameter properties
+    public IScopeTreeLookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter {
+      get { return (IScopeTreeLookupParameter<ISymbolicExpressionTree>)Parameters[SymbolicExpressionTreeParameterName]; }
+    }
+    public ILookupParameter<ResultCollection> ResultCollectionParameter {
+      get { return (ILookupParameter<ResultCollection>)Parameters[ResultCollectionParameterName]; }
+    }
+    #endregion
+    #region properties
+    public virtual bool EnabledByDefault {
+      get { return true; }
+    }
+    public ItemArray<ISymbolicExpressionTree> SymbolicExpressionTree {
+      get { return SymbolicExpressionTreeParameter.ActualValue; }
+    }
+    public ResultCollection ResultCollection {
+      get { return ResultCollectionParameter.ActualValue; }
+    }
+    #endregion
+    [StorableConstructor]
+    protected SymbolicDataAnalysisAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisAnalyzer(SymbolicDataAnalysisAnalyzer original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisAnalyzer()
+      : base() {
+      Parameters.Add(new ScopeTreeLookupParameter<ISymbolicExpressionTree>(SymbolicExpressionTreeParameterName, "The symbolic expression trees that should be analyzed."));
+      Parameters.Add(new LookupParameter<ResultCollection>(ResultCollectionParameterName, "The result collection to store the analysis results."));
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisBottomUpDiversityAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisBottomUpDiversityAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisBottomUpDiversityAnalyzer.cs	(revision 16337)
@@ -0,0 +1,48 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Analysis;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("SymbolicDataAnalysisBottomUpDiversityAnalyzer", "A diversity analyzer based on the bottom-up distance between trees.")]
+  [StorableClass]
+  public class SymbolicDataAnalysisBottomUpDiversityAnalyzer : PopulationSimilarityAnalyzer {
+    [StorableConstructor]
+    protected SymbolicDataAnalysisBottomUpDiversityAnalyzer(bool deserializing) : base(deserializing) { }
+
+    protected SymbolicDataAnalysisBottomUpDiversityAnalyzer(SymbolicDataAnalysisBottomUpDiversityAnalyzer original, Cloner cloner)
+      : base(original, cloner) {
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisBottomUpDiversityAnalyzer(this, cloner);
+    }
+
+    public SymbolicDataAnalysisBottomUpDiversityAnalyzer(SymbolicExpressionTreeBottomUpSimilarityCalculator similarityCalculator)
+      : base(new[] { similarityCalculator }) {
+      DiversityResultName = "Genotypic Diversity";
+      UpdateCounterParameter.ActualName = "GenotypicDiversityAnalyzerUpdateCounter";
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisBuildingBlockAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisBuildingBlockAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisBuildingBlockAnalyzer.cs	(revision 16337)
@@ -0,0 +1,222 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Analysis;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using static HeuristicLab.Problems.DataAnalysis.Symbolic.SymbolicExpressionHashExtensions;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic.Analyzers {
+  [Item("SymbolicDataAnalysisBuildingBlockAnalyzer", "An analyzer that uses tree hashing to identify the most common subtrees (building blocks) in the population")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisBuildingBlockAnalyzer : SymbolicDataAnalysisAnalyzer {
+    private const string BuildingBlocksResultName = "BuildingBlocks";
+    private const string SolutionUniquenessResultName = "SolutionUniqueness";
+    private const string MinimumSubtreeLengthParameterName = "MinimumSubtreeLength";
+    private const string SimplifyTreesParameterName = "SimplifyTrees";
+
+    private Dictionary<ulong, DataRow> hashToRow = new Dictionary<ulong, DataRow>();
+
+    #region parameters
+    public IValueLookupParameter<IntValue> MinimumSubtreeLengthParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MinimumSubtreeLengthParameterName]; }
+    }
+
+    public IValueLookupParameter<BoolValue> SimplifyTreesParameter {
+      get { return (IValueLookupParameter<BoolValue>)Parameters[SimplifyTreesParameterName]; }
+    }
+    #endregion
+
+    #region parameter properties
+    public IntValue MinimumSubtreeLength {
+      get { return MinimumSubtreeLengthParameter.ActualValue; }
+    }
+
+    public BoolValue SimplifyTrees {
+      get { return SimplifyTreesParameter.ActualValue; }
+    }
+    #endregion
+
+    public override void InitializeState() {
+      base.InitializeState();
+
+      hashToRow = new Dictionary<ulong, DataRow>();
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (!Parameters.ContainsKey(SimplifyTreesParameterName)) {
+        Parameters.Add(new ValueLookupParameter<BoolValue>(SimplifyTreesParameterName, new BoolValue(false)));
+      }
+    }
+
+    public SymbolicDataAnalysisBuildingBlockAnalyzer() {
+      Parameters.Add(new ValueLookupParameter<IntValue>(MinimumSubtreeLengthParameterName, new IntValue(3)));
+      Parameters.Add(new ValueLookupParameter<BoolValue>(SimplifyTreesParameterName, new BoolValue(false)));
+    }
+
+    private SymbolicDataAnalysisBuildingBlockAnalyzer(SymbolicDataAnalysisBuildingBlockAnalyzer original, Cloner cloner) : base(original, cloner) {
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisBuildingBlockAnalyzer(this, cloner);
+    }
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisBuildingBlockAnalyzer(bool deserializing) : base(deserializing) { }
+
+    private readonly Func<byte[], ulong> hashFunction = HashUtil.JSHash;
+
+    public override IOperation Apply() {
+      DataTable dt;
+
+      if (!ResultCollection.ContainsKey(BuildingBlocksResultName)) {
+        dt = new DataTable(BuildingBlocksResultName);
+        ResultCollection.Add(new Result(BuildingBlocksResultName, dt));
+      } else {
+        dt = (DataTable)ResultCollection[BuildingBlocksResultName].Value;
+      }
+
+      var minLength = MinimumSubtreeLength.Value - 1; // -1 because the HashNode.Size property returns the size without current node (-1)
+      var simplify = SimplifyTrees.Value;
+
+      var expressions = new Dictionary<ulong, string>();
+      var expressionCounts = new Dictionary<ulong, int>();
+
+      int totalCount = 0; // total number of examined subtrees
+
+      var hashes = new List<ulong>();
+      // count hashes
+      foreach (var tree in SymbolicExpressionTree) {
+        var hashNodes = tree.Root.GetSubtree(0).GetSubtree(0).MakeNodes();
+        var simplified = simplify ? hashNodes.Simplify(hashFunction) : hashNodes.Sort(hashFunction);
+        hashes.Add(simplified.Last().CalculatedHashValue); // maybe calculate aggregate hash instead
+
+        for (int i = 0; i < simplified.Length; i++) {
+          HashNode<ISymbolicExpressionTreeNode> s = simplified[i];
+          if (s.IsLeaf || s.Size < minLength) {
+            continue;
+          }
+          ++totalCount;
+          var hash = s.CalculatedHashValue;
+          if (expressions.ContainsKey(hash)) {
+            expressionCounts[hash]++;
+            continue;
+          }
+
+          var sb = new StringBuilder();
+          for (int j = i - s.Size; j < i; ++j) {
+            sb.Append(GetLabel(simplified[j].Data)).Append(" ");
+          }
+          sb.Append(GetLabel(simplified[i].Data));
+          expressions[hash] = sb.ToString();
+          expressionCounts[hash] = 1;
+        }
+      }
+
+      // fill in values for existing rows
+      foreach (var t in hashToRow) {
+        var hash = t.Key;
+        var row = t.Value;
+
+        expressionCounts.TryGetValue(hash, out int count);
+        row.Values.Add(count);
+      }
+
+      var nValues = dt.Rows.Any() ? dt.Rows.Max(x => x.Values.Count) : 0;
+
+      // check if we have new rows
+      foreach (var t in expressionCounts.OrderByDescending(x => x.Value).Take(10)) {
+        var hash = t.Key;
+        var count = t.Value;
+        var label = expressions[hash];
+
+        if (hashToRow.ContainsKey(hash)) {
+          continue;
+        }
+        var row = new DataRow(label) { VisualProperties = { StartIndexZero = true } };
+        if (nValues > 0) {
+          row.Values.AddRange(Enumerable.Repeat<double>(0, nValues - 1)); // pad with zeroes
+        }
+        row.Values.Add(count);
+        dt.Rows.Add(row);
+        hashToRow[hash] = row;
+      }
+
+      // compute solution uniqueness
+      DataTableHistory dth;
+      var counts = hashes.GroupBy(x => x).ToDictionary(x => x.Key, x => x.Count());
+      if (!ResultCollection.ContainsKey(SolutionUniquenessResultName)) {
+        dth = new DataTableHistory();
+        ResultCollection.Add(new Result(SolutionUniquenessResultName, dth));
+      } else {
+        dth = (DataTableHistory)ResultCollection[SolutionUniquenessResultName].Value;
+      }
+
+      var ct = new DataTable("Unique Solutions");
+      var ctr = new DataRow { VisualProperties = { StartIndexZero = true, ChartType = DataRowVisualProperties.DataRowChartType.Columns } };
+      ctr.Values.AddRange(hashes.Select(x => (double)counts[x]).OrderByDescending(x => x));
+      ct.Rows.Add(ctr);
+      dth.Add(ct);
+
+      var max = dth.Max(x => x.Rows.First().Values.Max());
+      foreach (var table in dth) {
+        table.VisualProperties.YAxisMinimumAuto = false;
+        table.VisualProperties.YAxisMaximumAuto = false;
+        table.VisualProperties.YAxisMinimumFixedValue = 0;
+        table.VisualProperties.YAxisMaximumFixedValue = max;
+      }
+
+      return base.Apply();
+    }
+
+    private static string GetLabel(ISymbolicExpressionTreeNode node) {
+      if (node is ConstantTreeNode constant) {
+        return "C";
+      }
+      if (node is VariableTreeNode variable) {
+        return variable.VariableName;
+      }
+      if (node.Symbol is Addition) {
+        return "+";
+      }
+      if (node.Symbol is Subtraction) {
+        return "-";
+      }
+      if (node.Symbol is Multiplication) {
+        return "*";
+      }
+      if (node.Symbol is Division) {
+        return "/";
+      }
+      return node.Symbol.ToString();
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveAnalyzer.cs	(revision 16337)
@@ -0,0 +1,76 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Abstract base class for multi objective symbolic data analysis analyzers.
+  /// </summary>
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisMultiObjectiveAnalyzer : SymbolicDataAnalysisAnalyzer, ISymbolicDataAnalysisMultiObjectiveAnalyzer {
+    private const string QualitiesParameterName = "Qualities";
+    private const string MaximizationParameterName = "Maximization";
+    private const string ApplyLinearScalingParameterName = "ApplyLinearScaling";
+    #region parameter properties
+    public IScopeTreeLookupParameter<DoubleArray> QualitiesParameter {
+      get { return (IScopeTreeLookupParameter<DoubleArray>)Parameters[QualitiesParameterName]; }
+    }
+    public ILookupParameter<BoolArray> MaximizationParameter {
+      get { return (ILookupParameter<BoolArray>)Parameters[MaximizationParameterName]; }
+    }
+    public ILookupParameter<BoolValue> ApplyLinearScalingParameter {
+      get { return (ILookupParameter<BoolValue>)Parameters[ApplyLinearScalingParameterName]; }
+    }
+    #endregion
+    #region properties
+    public ItemArray<DoubleArray> Qualities {
+      get { return QualitiesParameter.ActualValue; }
+    }
+    public BoolArray Maximization {
+      get { return MaximizationParameter.ActualValue; }
+    }
+    #endregion
+    [StorableConstructor]
+    protected SymbolicDataAnalysisMultiObjectiveAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisMultiObjectiveAnalyzer(SymbolicDataAnalysisMultiObjectiveAnalyzer original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisMultiObjectiveAnalyzer()
+      : base() {
+      Parameters.Add(new ScopeTreeLookupParameter<DoubleArray>(QualitiesParameterName, "The qualities of the trees that should be analyzed."));
+      Parameters.Add(new LookupParameter<BoolArray>(MaximizationParameterName, "The directions of optimization for each dimension."));
+      Parameters.Add(new LookupParameter<BoolValue>(ApplyLinearScalingParameterName, "Flag that indicates if the individual should be linearly scaled before evaluating."));
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (Parameters.ContainsKey(ApplyLinearScalingParameterName) && Parameters[ApplyLinearScalingParameterName] is LookupParameter<BoolValue>)
+        Parameters.Remove(ApplyLinearScalingParameterName);
+      if (!Parameters.ContainsKey(ApplyLinearScalingParameterName))
+        Parameters.Add(new LookupParameter<BoolValue>(ApplyLinearScalingParameterName, "Flag that indicates if the individual should be linearly scaled before evaluating."));
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer.cs	(revision 16337)
@@ -0,0 +1,182 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// An operator that analyzes the training best symbolic data analysis solution for multi objective symbolic data analysis problems.
+  /// </summary>
+  [Item("SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer", "An operator that analyzes the training best symbolic data analysis solution for multi objective symbolic data analysis problems.")]
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer<T> : SymbolicDataAnalysisMultiObjectiveAnalyzer
+    where T : class, ISymbolicDataAnalysisSolution {
+    private const string TrainingBestSolutionsParameterName = "Best training solutions";
+    private const string TrainingBestSolutionQualitiesParameterName = "Best training solution qualities";
+    private const string UpdateAlwaysParameterName = "Always update best solutions";
+    private const string TrainingBestSolutionParameterName = "Best training solution";
+
+    #region parameter properties
+    public ILookupParameter<ItemList<T>> TrainingBestSolutionsParameter {
+      get { return (ILookupParameter<ItemList<T>>)Parameters[TrainingBestSolutionsParameterName]; }
+    }
+    public ILookupParameter<ItemList<DoubleArray>> TrainingBestSolutionQualitiesParameter {
+      get { return (ILookupParameter<ItemList<DoubleArray>>)Parameters[TrainingBestSolutionQualitiesParameterName]; }
+    }
+    public IFixedValueParameter<BoolValue> UpdateAlwaysParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[UpdateAlwaysParameterName]; }
+    }
+    #endregion
+    #region properties
+    private ItemList<T> TrainingBestSolutions {
+      get { return TrainingBestSolutionsParameter.ActualValue; }
+      set { TrainingBestSolutionsParameter.ActualValue = value; }
+    }
+    private ItemList<DoubleArray> TrainingBestSolutionQualities {
+      get { return TrainingBestSolutionQualitiesParameter.ActualValue; }
+      set { TrainingBestSolutionQualitiesParameter.ActualValue = value; }
+    }
+    public bool UpdateAlways {
+      get { return UpdateAlwaysParameter.Value.Value; }
+      set { UpdateAlwaysParameter.Value.Value = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer(SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer<T> original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer()
+      : base() {
+      Parameters.Add(new LookupParameter<ItemList<T>>(TrainingBestSolutionsParameterName, "The training best (Pareto-optimal) symbolic data analysis solutions."));
+      Parameters.Add(new LookupParameter<ItemList<DoubleArray>>(TrainingBestSolutionQualitiesParameterName, "The qualities of the training best (Pareto-optimal) solutions."));
+      Parameters.Add(new FixedValueParameter<BoolValue>(UpdateAlwaysParameterName, "Determines if the best training solutions should always be updated regardless of its quality.", new BoolValue(false)));
+      UpdateAlwaysParameter.Hidden = true;
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (!Parameters.ContainsKey(UpdateAlwaysParameterName)) {
+        Parameters.Add(new FixedValueParameter<BoolValue>(UpdateAlwaysParameterName, "Determines if the best training solutions should always be updated regardless of its quality.", new BoolValue(false)));
+        UpdateAlwaysParameter.Hidden = true;
+      }
+    }
+
+    public override IOperation Apply() {
+      var results = ResultCollection;
+      // create empty parameter and result values
+      if (TrainingBestSolutions == null) {
+        TrainingBestSolutions = new ItemList<T>();
+        TrainingBestSolutionQualities = new ItemList<DoubleArray>();
+        results.Add(new Result(TrainingBestSolutionQualitiesParameter.Name, TrainingBestSolutionQualitiesParameter.Description, TrainingBestSolutionQualities));
+        results.Add(new Result(TrainingBestSolutionsParameter.Name, TrainingBestSolutionsParameter.Description, TrainingBestSolutions));
+      }
+
+      if (!results.ContainsKey(TrainingBestSolutionParameterName)) {
+        results.Add(new Result(TrainingBestSolutionParameterName, "", typeof(ISymbolicDataAnalysisSolution)));
+      }
+
+      //if the pareto front of best solutions shall be updated regardless of the quality, the list initialized empty to discard old solutions
+      List<double[]> trainingBestQualities;
+      if (UpdateAlways) {
+        trainingBestQualities = new List<double[]>();
+      } else {
+        trainingBestQualities = TrainingBestSolutionQualities.Select(x => x.ToArray()).ToList();
+      }
+
+      ISymbolicExpressionTree[] trees = SymbolicExpressionTree.ToArray();
+      List<double[]> qualities = Qualities.Select(x => x.ToArray()).ToList();
+      bool[] maximization = Maximization.ToArray();
+
+      var nonDominatedIndividuals = new[] { new { Tree = default(ISymbolicExpressionTree), Qualities = default(double[]) } }.ToList();
+      nonDominatedIndividuals.Clear();
+
+      // build list of new non-dominated solutions
+      for (int i = 0; i < trees.Length; i++) {
+        if (IsNonDominated(qualities[i], nonDominatedIndividuals.Select(ind => ind.Qualities), maximization) &&
+            IsNonDominated(qualities[i], trainingBestQualities, maximization)) {
+          for (int j = nonDominatedIndividuals.Count - 1; j >= 0; j--) {
+            if (IsBetterOrEqual(qualities[i], nonDominatedIndividuals[j].Qualities, maximization)) {
+              nonDominatedIndividuals.RemoveAt(j);
+            }
+          }
+          nonDominatedIndividuals.Add(new { Tree = trees[i], Qualities = qualities[i] });
+        }
+      }
+
+      var nonDominatedSolutions = nonDominatedIndividuals.Select(x => new { Solution = CreateSolution(x.Tree, x.Qualities), Qualities = x.Qualities }).ToList();
+      nonDominatedSolutions.ForEach(s => s.Solution.Name = string.Join(",", s.Qualities.Select(q => q.ToString())));
+
+      #region update Pareto-optimal solution archive
+      if (nonDominatedSolutions.Count > 0) {
+        //add old non-dominated solutions only if they are not dominated by one of the new solutions
+        for (int i = 0; i < trainingBestQualities.Count; i++) {
+          if (IsNonDominated(trainingBestQualities[i], nonDominatedSolutions.Select(x => x.Qualities), maximization)) {
+            nonDominatedSolutions.Add(new { Solution = TrainingBestSolutions[i], Qualities = TrainingBestSolutionQualities[i].ToArray() });
+          }
+        }
+
+        //assumes the the first objective is always the accuracy
+        var sortedNonDominatedSolutions = maximization[0]
+          ? nonDominatedSolutions.OrderByDescending(x => x.Qualities[0])
+          : nonDominatedSolutions.OrderBy(x => x.Qualities[0]);
+        var trainingBestSolution = sortedNonDominatedSolutions.Select(s => s.Solution).First();
+        results[TrainingBestSolutionParameterName].Value = trainingBestSolution;
+        TrainingBestSolutions = new ItemList<T>(sortedNonDominatedSolutions.Select(x => x.Solution));
+        results[TrainingBestSolutionsParameter.Name].Value = TrainingBestSolutions;
+        TrainingBestSolutionQualities = new ItemList<DoubleArray>(sortedNonDominatedSolutions.Select(x => new DoubleArray(x.Qualities)));
+        results[TrainingBestSolutionQualitiesParameter.Name].Value = TrainingBestSolutionQualities;
+      }
+      #endregion
+      return base.Apply();
+    }
+
+    protected abstract T CreateSolution(ISymbolicExpressionTree bestTree, double[] bestQuality);
+
+    private bool IsNonDominated(double[] point, IEnumerable<double[]> points, bool[] maximization) {
+      foreach (var refPoint in points) {
+        bool refPointDominatesPoint = IsBetterOrEqual(refPoint, point, maximization);
+        if (refPointDominatesPoint) return false;
+      }
+      return true;
+    }
+
+    private bool IsBetterOrEqual(double[] lhs, double[] rhs, bool[] maximization) {
+      for (int i = 0; i < lhs.Length; i++) {
+        var result = IsBetterOrEqual(lhs[i], rhs[i], maximization[i]);
+        if (!result) return false;
+      }
+      return true;
+    }
+
+    private bool IsBetterOrEqual(double lhs, double rhs, bool maximization) {
+      if (maximization) return lhs >= rhs;
+      else return lhs <= rhs;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveValidationAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveValidationAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveValidationAnalyzer.cs	(revision 16337)
@@ -0,0 +1,98 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Abstract base class for symbolic data analysis analyzers that validate a solution on a separate data partition using the evaluator.
+  /// </summary>
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisMultiObjectiveValidationAnalyzer<T, U> : SymbolicDataAnalysisMultiObjectiveAnalyzer,
+    ISymbolicDataAnalysisValidationAnalyzer<T, U>
+    where T : class, ISymbolicDataAnalysisMultiObjectiveEvaluator<U>
+    where U : class, IDataAnalysisProblemData {
+    private const string RandomParameterName = "Random";
+    private const string ProblemDataParameterName = "ProblemData";
+    private const string EvaluatorParameterName = "Evaluator";
+    private const string SymbolicDataAnalysisTreeInterpreterParameterName = "SymbolicDataAnalysisTreeInterpreter";
+    private const string ValidationPartitionParameterName = "ValidationPartition";
+    private const string RelativeNumberOfEvaluatedSamplesParameterName = "RelativeNumberOfEvaluatedSamples";
+
+    #region parameter properties
+    public ILookupParameter<IRandom> RandomParameter {
+      get { return (ILookupParameter<IRandom>)Parameters[RandomParameterName]; }
+    }
+    public ILookupParameter<U> ProblemDataParameter {
+      get { return (ILookupParameter<U>)Parameters[ProblemDataParameterName]; }
+    }
+    public ILookupParameter<T> EvaluatorParameter {
+      get { return (ILookupParameter<T>)Parameters[EvaluatorParameterName]; }
+    }
+    public ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicDataAnalysisTreeInterpreterParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>)Parameters[SymbolicDataAnalysisTreeInterpreterParameterName]; }
+    }
+    public IValueLookupParameter<IntRange> ValidationPartitionParameter {
+      get { return (IValueLookupParameter<IntRange>)Parameters[ValidationPartitionParameterName]; }
+    }
+    public IValueLookupParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter {
+      get { return (IValueLookupParameter<PercentValue>)Parameters[RelativeNumberOfEvaluatedSamplesParameterName]; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisMultiObjectiveValidationAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisMultiObjectiveValidationAnalyzer(SymbolicDataAnalysisMultiObjectiveValidationAnalyzer<T, U> original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisMultiObjectiveValidationAnalyzer()
+      : base() {
+      Parameters.Add(new ValueLookupParameter<IRandom>(RandomParameterName, "The random generator to use."));
+      Parameters.Add(new LookupParameter<U>(ProblemDataParameterName, "The problem data of the symbolic data analysis problem."));
+      Parameters.Add(new LookupParameter<T>(EvaluatorParameterName, "The operator to use for fitness evaluation on the validation partition."));
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>(SymbolicDataAnalysisTreeInterpreterParameterName, "The interpreter for symbolic data analysis expression trees."));
+      Parameters.Add(new ValueLookupParameter<IntRange>(ValidationPartitionParameterName, "The validation partition."));
+      Parameters.Add(new ValueLookupParameter<PercentValue>(RelativeNumberOfEvaluatedSamplesParameterName, "The relative number of samples of the dataset partition, which should be randomly chosen for evaluation between the start and end index."));
+    }
+
+    protected IEnumerable<int> GenerateRowsToEvaluate() {
+      int seed = RandomParameter.ActualValue.Next();
+      int samplesStart = ValidationPartitionParameter.ActualValue.Start;
+      int samplesEnd = ValidationPartitionParameter.ActualValue.End;
+      int testPartitionStart = ProblemDataParameter.ActualValue.TestPartition.Start;
+      int testPartitionEnd = ProblemDataParameter.ActualValue.TestPartition.End;
+
+      if (samplesEnd < samplesStart) throw new ArgumentException("Start value is larger than end value.");
+      int count = (int)((samplesEnd - samplesStart) * RelativeNumberOfEvaluatedSamplesParameter.ActualValue.Value);
+      if (count == 0) count = 1;
+      return RandomEnumerable.SampleRandomNumbers(seed, samplesStart, samplesEnd, count)
+        .Where(i => i < testPartitionStart || testPartitionEnd <= i);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer.cs	(revision 16337)
@@ -0,0 +1,197 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// An operator that analyzes the validation best symbolic data analysis solution for multi objective symbolic data analysis problems.
+  /// </summary>
+  [Item("SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer", "An operator that analyzes the validation best symbolic data analysis solution for multi objective symbolic data analysis problems.")]
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer<S, T, U> : SymbolicDataAnalysisMultiObjectiveValidationAnalyzer<T, U>,
+    ISymbolicDataAnalysisMultiObjectiveAnalyzer
+    where S : class, ISymbolicDataAnalysisSolution
+    where T : class, ISymbolicDataAnalysisMultiObjectiveEvaluator<U>
+    where U : class, IDataAnalysisProblemData {
+    private const string ValidationBestSolutionsParameterName = "Best validation solutions";
+    private const string ValidationBestSolutionQualitiesParameterName = "Best validation solution qualities";
+    private const string UpdateAlwaysParameterName = "Always update best solutions";
+
+    #region parameter properties
+    public ILookupParameter<ItemList<S>> ValidationBestSolutionsParameter {
+      get { return (ILookupParameter<ItemList<S>>)Parameters[ValidationBestSolutionsParameterName]; }
+    }
+    public ILookupParameter<ItemList<DoubleArray>> ValidationBestSolutionQualitiesParameter {
+      get { return (ILookupParameter<ItemList<DoubleArray>>)Parameters[ValidationBestSolutionQualitiesParameterName]; }
+    }
+    public IFixedValueParameter<BoolValue> UpdateAlwaysParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[UpdateAlwaysParameterName]; }
+    }
+    #endregion
+    #region properties
+    public ItemList<S> ValidationBestSolutions {
+      get { return ValidationBestSolutionsParameter.ActualValue; }
+      set { ValidationBestSolutionsParameter.ActualValue = value; }
+    }
+    public ItemList<DoubleArray> ValidationBestSolutionQualities {
+      get { return ValidationBestSolutionQualitiesParameter.ActualValue; }
+      set { ValidationBestSolutionQualitiesParameter.ActualValue = value; }
+    }
+    public BoolValue UpdateAlways {
+      get { return UpdateAlwaysParameter.Value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer(SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer<S, T, U> original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer()
+      : base() {
+      Parameters.Add(new LookupParameter<ItemList<S>>(ValidationBestSolutionsParameterName, "The validation best (Pareto-optimal) symbolic data analysis solutions."));
+      Parameters.Add(new LookupParameter<ItemList<DoubleArray>>(ValidationBestSolutionQualitiesParameterName, "The qualities of the validation best (Pareto-optimal) solutions."));
+      Parameters.Add(new FixedValueParameter<BoolValue>(UpdateAlwaysParameterName, "Determines if the best validation solutions should always be updated regardless of its quality.", new BoolValue(false)));
+      UpdateAlwaysParameter.Hidden = true;
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (!Parameters.ContainsKey(UpdateAlwaysParameterName)) {
+        Parameters.Add(new FixedValueParameter<BoolValue>(UpdateAlwaysParameterName, "Determines if the best training solutions should always be updated regardless of its quality.", new BoolValue(false)));
+        UpdateAlwaysParameter.Hidden = true;
+      }
+    }
+
+    public override IOperation Apply() {
+      IEnumerable<int> rows = GenerateRowsToEvaluate();
+      if (!rows.Any()) return base.Apply();
+
+      var results = ResultCollection;
+      // create empty parameter and result values
+      if (ValidationBestSolutions == null) {
+        ValidationBestSolutions = new ItemList<S>();
+        ValidationBestSolutionQualities = new ItemList<DoubleArray>();
+        results.Add(new Result(ValidationBestSolutionQualitiesParameter.Name, ValidationBestSolutionQualitiesParameter.Description, ValidationBestSolutionQualities));
+        results.Add(new Result(ValidationBestSolutionsParameter.Name, ValidationBestSolutionsParameter.Description, ValidationBestSolutions));
+      }
+
+      //if the pareto front of best solutions shall be updated regardless of the quality, the list initialized empty to discard old solutions
+      IList<double[]> trainingBestQualities;
+      if (UpdateAlways.Value) {
+        trainingBestQualities = new List<double[]>();
+      } else {
+        trainingBestQualities = ValidationBestSolutionQualities.Select(x => x.ToArray()).ToList();
+      }
+
+      #region find best trees
+      IList<int> nonDominatedIndexes = new List<int>();
+      ISymbolicExpressionTree[] tree = SymbolicExpressionTree.ToArray();
+      bool[] maximization = Maximization.ToArray();
+      List<double[]> newNonDominatedQualities = new List<double[]>();
+      var evaluator = EvaluatorParameter.ActualValue;
+      var problemData = ProblemDataParameter.ActualValue;
+      IExecutionContext childContext = (IExecutionContext)ExecutionContext.CreateChildOperation(evaluator);
+
+      var qualities = tree
+        .Select(t => evaluator.Evaluate(childContext, t, problemData, rows))
+        .ToArray();
+      for (int i = 0; i < tree.Length; i++) {
+        if (IsNonDominated(qualities[i], trainingBestQualities, maximization) &&
+          IsNonDominated(qualities[i], qualities, maximization)) {
+          if (!newNonDominatedQualities.Contains(qualities[i], new DoubleArrayComparer())) {
+            newNonDominatedQualities.Add(qualities[i]);
+            nonDominatedIndexes.Add(i);
+          }
+        }
+      }
+      #endregion
+      #region update Pareto-optimal solution archive
+      if (nonDominatedIndexes.Count > 0) {
+        ItemList<DoubleArray> nonDominatedQualities = new ItemList<DoubleArray>();
+        ItemList<S> nonDominatedSolutions = new ItemList<S>();
+        // add all new non-dominated solutions to the archive
+        foreach (var index in nonDominatedIndexes) {
+          S solution = CreateSolution(tree[index], qualities[index]);
+          nonDominatedSolutions.Add(solution);
+          nonDominatedQualities.Add(new DoubleArray(qualities[index]));
+        }
+        // add old non-dominated solutions only if they are not dominated by one of the new solutions
+        for (int i = 0; i < trainingBestQualities.Count; i++) {
+          if (IsNonDominated(trainingBestQualities[i], newNonDominatedQualities, maximization)) {
+            if (!newNonDominatedQualities.Contains(trainingBestQualities[i], new DoubleArrayComparer())) {
+              nonDominatedSolutions.Add(ValidationBestSolutions[i]);
+              nonDominatedQualities.Add(ValidationBestSolutionQualities[i]);
+            }
+          }
+        }
+
+        results[ValidationBestSolutionsParameter.Name].Value = nonDominatedSolutions;
+        results[ValidationBestSolutionQualitiesParameter.Name].Value = nonDominatedQualities;
+      }
+      #endregion
+      return base.Apply();
+    }
+
+    protected abstract S CreateSolution(ISymbolicExpressionTree bestTree, double[] bestQuality);
+
+    private bool IsNonDominated(double[] point, IList<double[]> points, bool[] maximization) {
+      foreach (var refPoint in points) {
+        bool refPointDominatesPoint = true;
+        for (int i = 0; i < point.Length; i++) {
+          refPointDominatesPoint &= IsBetter(refPoint[i], point[i], maximization[i]);
+        }
+        if (refPointDominatesPoint) return false;
+      }
+      return true;
+    }
+    private bool IsBetter(double lhs, double rhs, bool maximization) {
+      if (maximization) return lhs > rhs;
+      else return lhs < rhs;
+    }
+
+    private class DoubleArrayComparer : IEqualityComparer<double[]> {
+      public bool Equals(double[] x, double[] y) {
+        if (y.Length != x.Length) throw new ArgumentException();
+        for (int i = 0; i < x.Length; i++) {
+          if (!x[i].IsAlmost(y[i])) return false;
+        }
+        return true;
+      }
+
+      public int GetHashCode(double[] obj) {
+        int c = obj.Length;
+        for (int i = 0; i < obj.Length; i++)
+          c ^= obj[i].GetHashCode();
+        return c;
+      }
+    }
+
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveAnalyzer.cs	(revision 16337)
@@ -0,0 +1,77 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Abstract base class for single objective symbolic data analysis analyzers.
+  /// </summary>
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisSingleObjectiveAnalyzer : SymbolicDataAnalysisAnalyzer, ISymbolicDataAnalysisSingleObjectiveAnalyzer {
+    private const string QualityParameterName = "Quality";
+    private const string MaximizationParameterName = "Maximization";
+    private const string ApplyLinearScalingParameterName = "ApplyLinearScaling";
+
+    #region parameter properties
+    public IScopeTreeLookupParameter<DoubleValue> QualityParameter {
+      get { return (IScopeTreeLookupParameter<DoubleValue>)Parameters[QualityParameterName]; }
+    }
+    public ILookupParameter<BoolValue> MaximizationParameter {
+      get { return (ILookupParameter<BoolValue>)Parameters[MaximizationParameterName]; }
+    }
+    public ILookupParameter<BoolValue> ApplyLinearScalingParameter {
+      get { return (ILookupParameter<BoolValue>)Parameters[ApplyLinearScalingParameterName]; }
+    }
+    #endregion
+    #region properties
+    public ItemArray<DoubleValue> Quality {
+      get { return QualityParameter.ActualValue; }
+    }
+    public BoolValue Maximization {
+      get { return MaximizationParameter.ActualValue; }
+    }
+    #endregion
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectiveAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisSingleObjectiveAnalyzer(SymbolicDataAnalysisSingleObjectiveAnalyzer original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisSingleObjectiveAnalyzer()
+      : base() {
+      Parameters.Add(new ScopeTreeLookupParameter<DoubleValue>(QualityParameterName, "The qualities of the trees that should be analyzed."));
+      Parameters.Add(new LookupParameter<BoolValue>(MaximizationParameterName, "The direction of optimization."));
+      Parameters.Add(new LookupParameter<BoolValue>(ApplyLinearScalingParameterName, "Flag that indicates if the individual should be linearly scaled before evaluating."));
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (Parameters.ContainsKey(ApplyLinearScalingParameterName) && !(Parameters[ApplyLinearScalingParameterName] is LookupParameter<BoolValue>))
+        Parameters.Remove(ApplyLinearScalingParameterName);
+      if (!Parameters.ContainsKey(ApplyLinearScalingParameterName))
+        Parameters.Add(new LookupParameter<BoolValue>(ApplyLinearScalingParameterName, "Flag that indicates if the individual should be linearly scaled before evaluating."));
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectivePruningAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectivePruningAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectivePruningAnalyzer.cs	(revision 16337)
@@ -0,0 +1,276 @@
+﻿#region License Information
+
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#endregion
+
+using System;
+using System.Linq;
+using HeuristicLab.Analysis;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Operators;
+using HeuristicLab.Optimization.Operators;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicDataAnalysisSingleObjectivePruningAnalyzer", "An analyzer that prunes introns from trees in single objective symbolic data analysis problems.")]
+  public abstract class SymbolicDataAnalysisSingleObjectivePruningAnalyzer : SymbolicDataAnalysisSingleObjectiveAnalyzer {
+    #region parameter names
+    private const string ProblemDataParameterName = "ProblemData";
+    private const string UpdateIntervalParameterName = "UpdateInverval";
+    private const string UpdateCounterParameterName = "UpdateCounter";
+    private const string PopulationSliceParameterName = "PopulationSlice";
+    private const string PruningProbabilityParameterName = "PruningProbability";
+    private const string TotalNumberOfPrunedSubtreesParameterName = "Number of pruned subtrees";
+    private const string TotalNumberOfPrunedTreesParameterName = "Number of pruned trees";
+    private const string TotalNumberOfPrunedNodesParameterName = "Number of pruned nodes";
+    private const string RandomParameterName = "Random";
+    private const string ResultsParameterName = "Results";
+    private const string PopulationSizeParameterName = "PopulationSize";
+    #endregion
+
+    #region private members
+    private DataReducer prunedNodesReducer;
+    private DataReducer prunedSubtreesReducer;
+    private DataReducer prunedTreesReducer;
+    private DataTableValuesCollector valuesCollector;
+    private ResultsCollector resultsCollector;
+    #endregion
+
+    #region parameter properties
+    public ILookupParameter<IRandom> RandomParameter {
+      get { return (ILookupParameter<IRandom>)Parameters[RandomParameterName]; }
+    }
+    public IFixedValueParameter<IntValue> UpdateIntervalParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[UpdateIntervalParameterName]; }
+    }
+    public IFixedValueParameter<IntValue> UpdateCounterParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[UpdateCounterParameterName]; }
+    }
+    public IFixedValueParameter<DoubleRange> PopulationSliceParameter {
+      get { return (IFixedValueParameter<DoubleRange>)Parameters[PopulationSliceParameterName]; }
+    }
+    public IFixedValueParameter<DoubleValue> PruningProbabilityParameter {
+      get { return (IFixedValueParameter<DoubleValue>)Parameters[PruningProbabilityParameterName]; }
+    }
+    public ILookupParameter<IntValue> PopulationSizeParameter {
+      get { return (ILookupParameter<IntValue>)Parameters[PopulationSizeParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    protected abstract SymbolicDataAnalysisExpressionPruningOperator PruningOperator { get; }
+    protected int UpdateInterval { get { return UpdateIntervalParameter.Value.Value; } }
+
+    protected int UpdateCounter {
+      get { return UpdateCounterParameter.Value.Value; }
+      set { UpdateCounterParameter.Value.Value = value; }
+    }
+
+    protected double PopulationSliceStart {
+      get { return PopulationSliceParameter.Value.Start; }
+      set { PopulationSliceParameter.Value.Start = value; }
+    }
+
+    protected double PopulationSliceEnd {
+      get { return PopulationSliceParameter.Value.End; }
+      set { PopulationSliceParameter.Value.End = value; }
+    }
+
+    protected double PruningProbability {
+      get { return PruningProbabilityParameter.Value.Value; }
+      set { PruningProbabilityParameter.Value.Value = value; }
+    }
+    #endregion
+
+    #region IStatefulItem members
+    public override void InitializeState() {
+      base.InitializeState();
+      UpdateCounter = 0;
+    }
+    public override void ClearState() {
+      base.ClearState();
+      UpdateCounter = 0;
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectivePruningAnalyzer(bool deserializing) : base(deserializing) { }
+
+    protected SymbolicDataAnalysisSingleObjectivePruningAnalyzer(SymbolicDataAnalysisSingleObjectivePruningAnalyzer original, Cloner cloner)
+      : base(original, cloner) {
+      if (original.prunedNodesReducer != null)
+        this.prunedNodesReducer = (DataReducer)original.prunedNodesReducer.Clone();
+      if (original.prunedSubtreesReducer != null)
+        this.prunedSubtreesReducer = (DataReducer)original.prunedSubtreesReducer.Clone();
+      if (original.prunedTreesReducer != null)
+        this.prunedTreesReducer = (DataReducer)original.prunedTreesReducer.Clone();
+      if (original.valuesCollector != null)
+        this.valuesCollector = (DataTableValuesCollector)original.valuesCollector.Clone();
+      if (original.resultsCollector != null)
+        this.resultsCollector = (ResultsCollector)original.resultsCollector.Clone();
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (!Parameters.ContainsKey(PopulationSizeParameterName)) {
+        Parameters.Add(new LookupParameter<IntValue>(PopulationSizeParameterName, "The population of individuals."));
+      }
+      if (Parameters.ContainsKey(UpdateCounterParameterName)) {
+        var fixedValueParameter = Parameters[UpdateCounterParameterName] as FixedValueParameter<IntValue>;
+        if (fixedValueParameter == null) {
+          var valueParameter = (ValueParameter<IntValue>)Parameters[UpdateCounterParameterName];
+          Parameters.Remove(UpdateCounterParameterName);
+          Parameters.Add(new FixedValueParameter<IntValue>(UpdateCounterParameterName, valueParameter.Value));
+        }
+      }
+      if (Parameters.ContainsKey(UpdateIntervalParameterName)) {
+        var fixedValueParameter = Parameters[UpdateIntervalParameterName] as FixedValueParameter<IntValue>;
+        if (fixedValueParameter == null) {
+          var valueParameter = (ValueParameter<IntValue>)Parameters[UpdateIntervalParameterName];
+          Parameters.Remove(UpdateIntervalParameterName);
+          Parameters.Add(new FixedValueParameter<IntValue>(UpdateIntervalParameterName, valueParameter.Value));
+        }
+      }
+      if (Parameters.ContainsKey(PopulationSliceParameterName)) {
+        var fixedValueParameter = Parameters[PopulationSliceParameterName] as FixedValueParameter<DoubleRange>;
+        if (fixedValueParameter == null) {
+          var valueParameter = (ValueParameter<DoubleRange>)Parameters[PopulationSliceParameterName];
+          Parameters.Remove(PopulationSliceParameterName);
+          Parameters.Add(new FixedValueParameter<DoubleRange>(PopulationSliceParameterName, valueParameter.Value));
+        }
+      }
+      if (Parameters.ContainsKey(PruningProbabilityParameterName)) {
+        var fixedValueParameter = Parameters[PruningProbabilityParameterName] as FixedValueParameter<DoubleValue>;
+        if (fixedValueParameter == null) {
+          var valueParameter = (ValueParameter<DoubleValue>)Parameters[PruningProbabilityParameterName];
+          Parameters.Remove(PruningProbabilityParameterName);
+          Parameters.Add(new FixedValueParameter<DoubleValue>(PruningProbabilityParameterName, valueParameter.Value));
+        }
+      }
+    }
+
+    protected SymbolicDataAnalysisSingleObjectivePruningAnalyzer() {
+      #region add parameters
+      Parameters.Add(new FixedValueParameter<DoubleRange>(PopulationSliceParameterName, "The slice of the population where pruning should be applied.", new DoubleRange(0.75, 1)));
+      Parameters.Add(new FixedValueParameter<DoubleValue>(PruningProbabilityParameterName, "The probability for pruning an individual.", new DoubleValue(0.5)));
+      Parameters.Add(new FixedValueParameter<IntValue>(UpdateIntervalParameterName, "The interval in which the tree length analysis should be applied.", new IntValue(1)));
+      Parameters.Add(new FixedValueParameter<IntValue>(UpdateCounterParameterName, "The value which counts how many times the operator was called", new IntValue(0)));
+      Parameters.Add(new LookupParameter<IRandom>(RandomParameterName, "The random number generator."));
+      Parameters.Add(new LookupParameter<IDataAnalysisProblemData>(ProblemDataParameterName, "The problem data."));
+      Parameters.Add(new LookupParameter<IntValue>(PopulationSizeParameterName, "The population of individuals."));
+      #endregion
+    }
+
+    // 
+    /// <summary>
+    /// Computes the closed interval bounding the portion of the population that is to be pruned. 
+    /// </summary>
+    /// <returns>Returns an int range [start, end]</returns>
+    private IntRange GetSliceBounds() {
+      if (PopulationSliceStart < 0 || PopulationSliceEnd < 0) throw new ArgumentOutOfRangeException("The slice bounds cannot be negative.");
+      if (PopulationSliceStart > 1 || PopulationSliceEnd > 1) throw new ArgumentOutOfRangeException("The slice bounds should be expressed as unit percentages.");
+      var count = PopulationSizeParameter.ActualValue.Value;
+      var start = (int)Math.Round(PopulationSliceStart * count);
+      var end = (int)Math.Round(PopulationSliceEnd * count);
+      if (end > count) end = count;
+
+      if (start >= end) throw new ArgumentOutOfRangeException("Invalid PopulationSlice bounds.");
+      return new IntRange(start, end);
+    }
+
+    private IOperation CreatePruningOperation() {
+      var operations = new OperationCollection { Parallel = true };
+      var range = GetSliceBounds();
+      var qualities = Quality.Select(x => x.Value).ToArray();
+      var indices = Enumerable.Range(0, qualities.Length).ToArray();
+      indices.StableSort((a, b) => qualities[a].CompareTo(qualities[b]));
+
+      if (!Maximization.Value) Array.Reverse(indices);
+
+      var subscopes = ExecutionContext.Scope.SubScopes;
+      var random = RandomParameter.ActualValue;
+
+      var empty = new EmptyOperator();
+
+      for (int i = 0; i < indices.Length; ++i) {
+        IOperator @operator;
+        if (range.Start <= i && i < range.End && random.NextDouble() <= PruningProbability)
+          @operator = PruningOperator;
+        else @operator = empty;
+        var index = indices[i];
+        var subscope = subscopes[index];
+        operations.Add(ExecutionContext.CreateChildOperation(@operator, subscope));
+      }
+      return operations;
+    }
+
+    public override IOperation Apply() {
+      UpdateCounter++;
+      if (UpdateCounter != UpdateInterval) return base.Apply();
+      UpdateCounter = 0;
+
+      if (prunedNodesReducer == null || prunedSubtreesReducer == null || prunedTreesReducer == null || valuesCollector == null || resultsCollector == null) { InitializeOperators(); }
+
+      var prune = CreatePruningOperation();
+      var reducePrunedNodes = ExecutionContext.CreateChildOperation(prunedNodesReducer);
+      var reducePrunedSubtrees = ExecutionContext.CreateChildOperation(prunedSubtreesReducer);
+      var reducePrunedTrees = ExecutionContext.CreateChildOperation(prunedTreesReducer);
+      var collectValues = ExecutionContext.CreateChildOperation(valuesCollector);
+      var collectResults = ExecutionContext.CreateChildOperation(resultsCollector);
+
+      return new OperationCollection { prune, reducePrunedNodes, reducePrunedSubtrees, reducePrunedTrees, collectValues, collectResults, base.Apply() };
+    }
+
+    private void InitializeOperators() {
+      prunedNodesReducer = new DataReducer();
+      prunedNodesReducer.ParameterToReduce.ActualName = PruningOperator.PrunedNodesParameter.ActualName;
+      prunedNodesReducer.ReductionOperation.Value = new ReductionOperation(ReductionOperations.Sum); // sum all the pruned subtrees parameter values
+      prunedNodesReducer.TargetOperation.Value = new ReductionOperation(ReductionOperations.Assign); // asign the sum to the target parameter
+      prunedNodesReducer.TargetParameter.ActualName = TotalNumberOfPrunedNodesParameterName;
+
+      prunedSubtreesReducer = new DataReducer();
+      prunedSubtreesReducer.ParameterToReduce.ActualName = PruningOperator.PrunedSubtreesParameter.ActualName;
+      prunedSubtreesReducer.ReductionOperation.Value = new ReductionOperation(ReductionOperations.Sum); // sum all the pruned subtrees parameter values
+      prunedSubtreesReducer.TargetOperation.Value = new ReductionOperation(ReductionOperations.Assign); // asign the sum to the target parameter
+      prunedSubtreesReducer.TargetParameter.ActualName = TotalNumberOfPrunedSubtreesParameterName;
+
+      prunedTreesReducer = new DataReducer();
+      prunedTreesReducer.ParameterToReduce.ActualName = PruningOperator.PrunedTreesParameter.ActualName;
+      prunedTreesReducer.ReductionOperation.Value = new ReductionOperation(ReductionOperations.Sum);
+      prunedTreesReducer.TargetOperation.Value = new ReductionOperation(ReductionOperations.Assign);
+      prunedTreesReducer.TargetParameter.ActualName = TotalNumberOfPrunedTreesParameterName;
+
+      valuesCollector = new DataTableValuesCollector();
+      valuesCollector.CollectedValues.Add(new LookupParameter<IntValue>(TotalNumberOfPrunedNodesParameterName));
+      valuesCollector.CollectedValues.Add(new LookupParameter<IntValue>(TotalNumberOfPrunedSubtreesParameterName));
+      valuesCollector.CollectedValues.Add(new LookupParameter<IntValue>(TotalNumberOfPrunedTreesParameterName));
+      valuesCollector.DataTableParameter.ActualName = "Population pruning";
+
+      resultsCollector = new ResultsCollector();
+      resultsCollector.CollectedValues.Add(new LookupParameter<DataTable>("Population pruning"));
+      resultsCollector.ResultsParameter.ActualName = ResultsParameterName;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer.cs	(revision 16337)
@@ -0,0 +1,185 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// An operator that analyzes the training best symbolic data analysis solution for single objective symbolic data analysis problems.
+  /// </summary>
+  [Item("SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer", "An operator that analyzes the training best symbolic data analysis solution for single objective symbolic data analysis problems.")]
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer<T> : SymbolicDataAnalysisSingleObjectiveAnalyzer, IIterationBasedOperator where T : class, ISymbolicDataAnalysisSolution {
+    private const string TrainingBestSolutionParameterName = "Best training solution";
+    private const string TrainingBestSolutionQualityParameterName = "Best training solution quality";
+    private const string TrainingBestSolutionGenerationParameterName = "Best training solution generation";
+    private const string TrainingBestSolutionsHistoryParameterName = "Best training solutions history";
+    private const string UpdateAlwaysParameterName = "Always update best solution";
+    private const string IterationsParameterName = "Iterations";
+    private const string MaximumIterationsParameterName = "Maximum Iterations";
+    private const string StoreHistoryParameterName = "Store History";
+
+    #region parameter properties
+    public ILookupParameter<T> TrainingBestSolutionParameter {
+      get { return (ILookupParameter<T>)Parameters[TrainingBestSolutionParameterName]; }
+    }
+    public ILookupParameter<DoubleValue> TrainingBestSolutionQualityParameter {
+      get { return (ILookupParameter<DoubleValue>)Parameters[TrainingBestSolutionQualityParameterName]; }
+    }
+    public ILookupParameter<IntValue> TrainingBestSolutionGenerationParameter {
+      get { return (ILookupParameter<IntValue>)Parameters[TrainingBestSolutionGenerationParameterName]; }
+    }
+    public ILookupParameter<ItemList<T>> TrainingBestSolutionsHistoryParameter {
+      get { return (ILookupParameter<ItemList<T>>)Parameters[TrainingBestSolutionsHistoryParameterName]; }
+    }
+    public IFixedValueParameter<BoolValue> UpdateAlwaysParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[UpdateAlwaysParameterName]; }
+    }
+    public ILookupParameter<IntValue> IterationsParameter {
+      get { return (ILookupParameter<IntValue>)Parameters[IterationsParameterName]; }
+    }
+    public IValueLookupParameter<IntValue> MaximumIterationsParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumIterationsParameterName]; }
+    }
+
+    public IFixedValueParameter<BoolValue> StoreHistoryParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[StoreHistoryParameterName]; }
+    }
+    #endregion
+    #region properties
+    public T TrainingBestSolution {
+      get { return TrainingBestSolutionParameter.ActualValue; }
+      set { TrainingBestSolutionParameter.ActualValue = value; }
+    }
+    public DoubleValue TrainingBestSolutionQuality {
+      get { return TrainingBestSolutionQualityParameter.ActualValue; }
+      set { TrainingBestSolutionQualityParameter.ActualValue = value; }
+    }
+    public bool UpdateAlways {
+      get { return UpdateAlwaysParameter.Value.Value; }
+      set { UpdateAlwaysParameter.Value.Value = value; }
+    }
+
+    public bool StoreHistory {
+      get { return StoreHistoryParameter.Value.Value; }
+      set { StoreHistoryParameter.Value.Value = value; }
+    }
+    #endregion
+
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer(SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer<T> original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer()
+      : base() {
+      Parameters.Add(new LookupParameter<T>(TrainingBestSolutionParameterName, "The best training symbolic data analyis solution."));
+      Parameters.Add(new LookupParameter<DoubleValue>(TrainingBestSolutionQualityParameterName, "The quality of the training best symbolic data analysis solution."));
+      Parameters.Add(new LookupParameter<IntValue>(TrainingBestSolutionGenerationParameterName, "The generation in which the best training solution was found."));
+      Parameters.Add(new FixedValueParameter<BoolValue>(UpdateAlwaysParameterName, "Determines if the best training solution should always be updated regardless of its quality.", new BoolValue(false)));
+      Parameters.Add(new LookupParameter<IntValue>(IterationsParameterName, "The number of performed iterations."));
+      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumIterationsParameterName, "The maximum number of performed iterations.") { Hidden = true });
+      Parameters.Add(new FixedValueParameter<BoolValue>(StoreHistoryParameterName, "Flag that determines whether all encountered best solutions should be stored as results.", new BoolValue(false)));
+      Parameters.Add(new LookupParameter<ItemList<T>>(TrainingBestSolutionsHistoryParameterName, "The history of the best training symbolic data analysis solutions."));
+      UpdateAlwaysParameter.Hidden = true;
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (!Parameters.ContainsKey(UpdateAlwaysParameterName)) {
+        Parameters.Add(new FixedValueParameter<BoolValue>(UpdateAlwaysParameterName, "Determines if the best training solution should always be updated regardless of its quality.", new BoolValue(false)));
+        UpdateAlwaysParameter.Hidden = true;
+      }
+      if (!Parameters.ContainsKey(TrainingBestSolutionGenerationParameterName))
+        Parameters.Add(new LookupParameter<IntValue>(TrainingBestSolutionGenerationParameterName, "The generation in which the best training solution was found."));
+      if (!Parameters.ContainsKey(IterationsParameterName))
+        Parameters.Add(new LookupParameter<IntValue>(IterationsParameterName, "The number of performed iterations."));
+      if (!Parameters.ContainsKey(MaximumIterationsParameterName))
+        Parameters.Add(new ValueLookupParameter<IntValue>(MaximumIterationsParameterName, "The maximum number of performed iterations.") { Hidden = true });
+      if (!Parameters.ContainsKey(StoreHistoryParameterName))
+        Parameters.Add(new FixedValueParameter<BoolValue>(StoreHistoryParameterName, "Flag that determines whether all encountered best solutions should be stored as results.", new BoolValue(false)));
+      if (!Parameters.ContainsKey(TrainingBestSolutionsHistoryParameterName))
+        Parameters.Add(new LookupParameter<ItemList<T>>(TrainingBestSolutionsHistoryParameterName, "The history of the best training symbolic data analysis solutions."));
+    }
+
+    public override IOperation Apply() {
+      var results = ResultCollection;
+      #region create results
+      if (!results.ContainsKey(TrainingBestSolutionParameter.Name))
+        results.Add(new Result(TrainingBestSolutionParameter.Name, TrainingBestSolutionParameter.Description, typeof(T)));
+      if (!results.ContainsKey(TrainingBestSolutionQualityParameter.Name))
+        results.Add(new Result(TrainingBestSolutionQualityParameter.Name, TrainingBestSolutionQualityParameter.Description, typeof(DoubleValue)));
+      if (!results.ContainsKey(TrainingBestSolutionGenerationParameter.Name) && IterationsParameter.ActualValue != null)
+        results.Add(new Result(TrainingBestSolutionGenerationParameter.Name, TrainingBestSolutionGenerationParameter.Description, typeof(IntValue)));
+      if (StoreHistory && !results.ContainsKey(TrainingBestSolutionsHistoryParameter.Name)) {
+
+        results.Add(new Result(TrainingBestSolutionsHistoryParameter.Name, TrainingBestSolutionsHistoryParameter.Description, typeof(ItemList<T>)));
+        TrainingBestSolutionsHistoryParameter.ActualValue = new ItemList<T>();
+        results[TrainingBestSolutionsHistoryParameter.Name].Value = TrainingBestSolutionsHistoryParameter.ActualValue;
+      }
+      #endregion
+
+      #region find best tree
+      double bestQuality = Maximization.Value ? double.NegativeInfinity : double.PositiveInfinity;
+      ISymbolicExpressionTree bestTree = null;
+      ISymbolicExpressionTree[] tree = SymbolicExpressionTree.ToArray();
+      double[] quality = Quality.Select(x => x.Value).ToArray();
+      for (int i = 0; i < tree.Length; i++) {
+        if (IsBetter(quality[i], bestQuality, Maximization.Value)) {
+          bestQuality = quality[i];
+          bestTree = tree[i];
+        }
+      }
+      #endregion
+
+      if (bestTree != null && (UpdateAlways || TrainingBestSolutionQuality == null ||
+        IsBetter(bestQuality, TrainingBestSolutionQuality.Value, Maximization.Value))) {
+        TrainingBestSolution = CreateSolution(bestTree, bestQuality);
+        TrainingBestSolutionQuality = new DoubleValue(bestQuality);
+        if (IterationsParameter.ActualValue != null)
+          TrainingBestSolutionGenerationParameter.ActualValue = new IntValue(IterationsParameter.ActualValue.Value);
+
+        results[TrainingBestSolutionParameter.Name].Value = TrainingBestSolution;
+        results[TrainingBestSolutionQualityParameter.Name].Value = TrainingBestSolutionQuality;
+        if (TrainingBestSolutionGenerationParameter.ActualValue != null)
+          results[TrainingBestSolutionGenerationParameter.Name].Value = TrainingBestSolutionGenerationParameter.ActualValue;
+
+        if (StoreHistory) {
+          TrainingBestSolutionsHistoryParameter.ActualValue.Add(TrainingBestSolution);
+        }
+      }
+      return base.Apply();
+    }
+
+    protected abstract T CreateSolution(ISymbolicExpressionTree bestTree, double bestQuality);
+
+    private bool IsBetter(double lhs, double rhs, bool maximization) {
+      if (maximization) return lhs > rhs;
+      else return lhs < rhs;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer.cs	(revision 16337)
@@ -0,0 +1,191 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// An operator that collects the Pareto-best symbolic data analysis solutions for single objective symbolic data analysis problems.
+  /// </summary>
+  [Item("SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer", "An operator that analyzes the Pareto-best symbolic data analysis solution for single objective symbolic data analysis problems.")]
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer<S, T> : SymbolicDataAnalysisSingleObjectiveAnalyzer, ISymbolicDataAnalysisInterpreterOperator, ISymbolicDataAnalysisBoundedOperator
+    where T : class, ISymbolicDataAnalysisSolution
+    where S : class, IDataAnalysisProblemData {
+    private const string ProblemDataParameterName = "ProblemData";
+    private const string TrainingBestSolutionsParameterName = "Best training solutions";
+    private const string TrainingBestSolutionQualitiesParameterName = "Best training solution qualities";
+    private const string ComplexityParameterName = "Complexity";
+    private const string SymbolicDataAnalysisTreeInterpreterParameterName = "SymbolicDataAnalysisTreeInterpreter";
+    private const string EstimationLimitsParameterName = "EstimationLimits";
+
+    public override bool EnabledByDefault {
+      get { return false; }
+    }
+
+    #region parameter properties
+    public ILookupParameter<ItemList<T>> TrainingBestSolutionsParameter {
+      get { return (ILookupParameter<ItemList<T>>)Parameters[TrainingBestSolutionsParameterName]; }
+    }
+    public ILookupParameter<ItemList<DoubleArray>> TrainingBestSolutionQualitiesParameter {
+      get { return (ILookupParameter<ItemList<DoubleArray>>)Parameters[TrainingBestSolutionQualitiesParameterName]; }
+    }
+    public IScopeTreeLookupParameter<DoubleValue> ComplexityParameter {
+      get { return (IScopeTreeLookupParameter<DoubleValue>)Parameters[ComplexityParameterName]; }
+    }
+    public ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicDataAnalysisTreeInterpreterParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>)Parameters[SymbolicDataAnalysisTreeInterpreterParameterName]; }
+    }
+    public ILookupParameter<S> ProblemDataParameter {
+      get { return (ILookupParameter<S>)Parameters[ProblemDataParameterName]; }
+    }
+    public IValueLookupParameter<DoubleLimit> EstimationLimitsParameter {
+      get { return (IValueLookupParameter<DoubleLimit>)Parameters[EstimationLimitsParameterName]; }
+    }
+    #endregion
+    #region properties
+    public ItemList<T> TrainingBestSolutions {
+      get { return TrainingBestSolutionsParameter.ActualValue; }
+      set { TrainingBestSolutionsParameter.ActualValue = value; }
+    }
+    public ItemList<DoubleArray> TrainingBestSolutionQualities {
+      get { return TrainingBestSolutionQualitiesParameter.ActualValue; }
+      set { TrainingBestSolutionQualitiesParameter.ActualValue = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer(SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer<S, T> original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer()
+      : base() {
+      Parameters.Add(new LookupParameter<S>(ProblemDataParameterName, "The problem data for the symbolic data analysis solution."));
+      Parameters.Add(new LookupParameter<ItemList<T>>(TrainingBestSolutionsParameterName, "The training best (Pareto-optimal) symbolic data analysis solutions."));
+      Parameters.Add(new LookupParameter<ItemList<DoubleArray>>(TrainingBestSolutionQualitiesParameterName, "The qualities of the training best (Pareto-optimal) solutions."));
+      Parameters.Add(new ScopeTreeLookupParameter<DoubleValue>(ComplexityParameterName, "The complexity of each tree."));
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>(SymbolicDataAnalysisTreeInterpreterParameterName, "The symbolic data analysis tree interpreter for the symbolic expression tree."));
+      Parameters.Add(new ValueLookupParameter<DoubleLimit>(EstimationLimitsParameterName, "The lower and upper limit for the estimated values produced by the symbolic classification model."));
+    }
+
+    public override IOperation Apply() {
+      var results = ResultCollection;
+      // create empty parameter and result values
+      if (TrainingBestSolutions == null) {
+        TrainingBestSolutions = new ItemList<T>();
+        TrainingBestSolutionQualities = new ItemList<DoubleArray>();
+        results.Add(new Result(TrainingBestSolutionQualitiesParameter.Name, TrainingBestSolutionQualitiesParameter.Description, TrainingBestSolutionQualities));
+        results.Add(new Result(TrainingBestSolutionsParameter.Name, TrainingBestSolutionsParameter.Description, TrainingBestSolutions));
+      }
+
+      IList<Tuple<double, double>> trainingBestQualities = TrainingBestSolutionQualities
+        .Select(x => Tuple.Create(x[0], x[1]))
+        .ToList();
+
+      #region find best trees
+      IList<int> nonDominatedIndexes = new List<int>();
+      ISymbolicExpressionTree[] tree = SymbolicExpressionTree.ToArray();
+      List<double> qualities = Quality.Select(x => x.Value).ToList();
+
+      List<double> complexities;
+      if (ComplexityParameter.ActualValue != null && ComplexityParameter.ActualValue.Length == qualities.Count) {
+        complexities = ComplexityParameter.ActualValue.Select(x => x.Value).ToList();
+      } else {
+        complexities = tree.Select(t => (double)t.Length).ToList();
+      }
+      List<Tuple<double, double>> fitness = new List<Tuple<double, double>>();
+      for (int i = 0; i < qualities.Count; i++)
+        fitness.Add(Tuple.Create(qualities[i], complexities[i]));
+      var maximization = Tuple.Create(Maximization.Value, false);// complexity must be minimized
+      List<Tuple<double, double>> newNonDominatedQualities = new List<Tuple<double, double>>();
+      for (int i = 0; i < tree.Length; i++) {
+        if (IsNonDominated(fitness[i], trainingBestQualities, maximization) &&
+          IsNonDominated(fitness[i], newNonDominatedQualities, maximization) &&
+          IsNonDominated(fitness[i], fitness.Skip(i + 1), maximization)) {
+          if (!newNonDominatedQualities.Contains(fitness[i])) {
+            newNonDominatedQualities.Add(fitness[i]);
+            nonDominatedIndexes.Add(i);
+          }
+        }
+      }
+      #endregion
+
+      #region update Pareto-optimal solution archive
+      if (nonDominatedIndexes.Count > 0) {
+        ItemList<DoubleArray> nonDominatedQualities = new ItemList<DoubleArray>();
+        ItemList<T> nonDominatedSolutions = new ItemList<T>();
+        // add all new non-dominated solutions to the archive
+        foreach (var index in nonDominatedIndexes) {
+          T solution = CreateSolution(tree[index]);
+          nonDominatedSolutions.Add(solution);
+          nonDominatedQualities.Add(new DoubleArray(new double[] { fitness[index].Item1, fitness[index].Item2 }));
+        }
+        // add old non-dominated solutions only if they are not dominated by one of the new solutions
+        for (int i = 0; i < trainingBestQualities.Count; i++) {
+          if (IsNonDominated(trainingBestQualities[i], newNonDominatedQualities, maximization)) {
+            if (!newNonDominatedQualities.Contains(trainingBestQualities[i])) {
+              nonDominatedSolutions.Add(TrainingBestSolutions[i]);
+              nonDominatedQualities.Add(TrainingBestSolutionQualities[i]);
+            }
+          }
+        }
+
+        // make sure solutions and qualities are ordered in the results
+        var orderedIndexes =
+          nonDominatedSolutions.Select((s, i) => i).OrderBy(i => nonDominatedQualities[i][0]).ToArray();
+
+        var orderedNonDominatedSolutions = new ItemList<T>();
+        var orderedNonDominatedQualities = new ItemList<DoubleArray>();
+        foreach (var i in orderedIndexes) {
+          orderedNonDominatedQualities.Add(nonDominatedQualities[i]);
+          orderedNonDominatedSolutions.Add(nonDominatedSolutions[i]);
+        }
+
+        TrainingBestSolutions = orderedNonDominatedSolutions;
+        TrainingBestSolutionQualities = orderedNonDominatedQualities;
+
+        results[TrainingBestSolutionsParameter.Name].Value = orderedNonDominatedSolutions;
+        results[TrainingBestSolutionQualitiesParameter.Name].Value = orderedNonDominatedQualities;
+      }
+      #endregion
+      return base.Apply();
+    }
+
+    protected abstract T CreateSolution(ISymbolicExpressionTree bestTree);
+
+    private bool IsNonDominated(Tuple<double, double> point, IEnumerable<Tuple<double, double>> points, Tuple<bool, bool> maximization) {
+      return !points.Any(p => IsBetterOrEqual(p.Item1, point.Item1, maximization.Item1) &&
+                             IsBetterOrEqual(p.Item2, point.Item2, maximization.Item2));
+    }
+    private bool IsBetterOrEqual(double lhs, double rhs, bool maximization) {
+      if (maximization) return lhs >= rhs;
+      else return lhs <= rhs;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationAnalyzer.cs	(revision 16337)
@@ -0,0 +1,112 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Abstract base class for symbolic data analysis analyzers that validate a solution on a separate data partition using the evaluator.
+  /// </summary>
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisSingleObjectiveValidationAnalyzer<T, U> : SymbolicDataAnalysisSingleObjectiveAnalyzer,
+    ISymbolicDataAnalysisValidationAnalyzer<T, U>, IStochasticOperator
+    where T : class, ISymbolicDataAnalysisSingleObjectiveEvaluator<U>
+    where U : class, IDataAnalysisProblemData {
+    private const string RandomParameterName = "Random";
+    private const string ProblemDataParameterName = "ProblemData";
+    private const string EvaluatorParameterName = "Evaluator";
+    private const string SymbolicDataAnalysisTreeInterpreterParameterName = "SymbolicDataAnalysisTreeInterpreter";
+    private const string ValidationPartitionParameterName = "ValidationPartition";
+    private const string RelativeNumberOfEvaluatedSamplesParameterName = "RelativeNumberOfEvaluatedSamples";
+    private const string PercentageOfBestSolutionsParameterName = "PercentageOfBestSolutions";
+
+    #region parameter properties
+    public ILookupParameter<IRandom> RandomParameter {
+      get { return (ILookupParameter<IRandom>)Parameters[RandomParameterName]; }
+    }
+    public ILookupParameter<U> ProblemDataParameter {
+      get { return (ILookupParameter<U>)Parameters[ProblemDataParameterName]; }
+    }
+    public ILookupParameter<T> EvaluatorParameter {
+      get { return (ILookupParameter<T>)Parameters[EvaluatorParameterName]; }
+    }
+    public ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicDataAnalysisTreeInterpreterParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>)Parameters[SymbolicDataAnalysisTreeInterpreterParameterName]; }
+    }
+    public IValueLookupParameter<IntRange> ValidationPartitionParameter {
+      get { return (IValueLookupParameter<IntRange>)Parameters[ValidationPartitionParameterName]; }
+    }
+    public IValueLookupParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter {
+      get { return (IValueLookupParameter<PercentValue>)Parameters[RelativeNumberOfEvaluatedSamplesParameterName]; }
+    }
+    public IValueLookupParameter<PercentValue> PercentageOfBestSolutionsParameter {
+      get { return (IValueLookupParameter<PercentValue>)Parameters[PercentageOfBestSolutionsParameterName]; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectiveValidationAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisSingleObjectiveValidationAnalyzer(SymbolicDataAnalysisSingleObjectiveValidationAnalyzer<T, U> original, Cloner cloner)
+      : base(original, cloner) {
+    }
+
+    protected SymbolicDataAnalysisSingleObjectiveValidationAnalyzer(): base() {
+      Parameters.Add(new LookupParameter<IRandom>(RandomParameterName, "The random generator."));
+      Parameters.Add(new LookupParameter<U>(ProblemDataParameterName, "The problem data of the symbolic data analysis problem."));
+      Parameters.Add(new LookupParameter<T>(EvaluatorParameterName, "The operator to use for fitness evaluation on the validation partition."));
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>(SymbolicDataAnalysisTreeInterpreterParameterName, "The interpreter for symbolic data analysis expression trees."));
+      Parameters.Add(new ValueLookupParameter<IntRange>(ValidationPartitionParameterName, "The validation partition."));
+      Parameters.Add(new ValueLookupParameter<PercentValue>(RelativeNumberOfEvaluatedSamplesParameterName, "The relative number of samples of the dataset partition, which should be randomly chosen for evaluation between the start and end index."));
+      Parameters.Add(new ValueLookupParameter<PercentValue>(PercentageOfBestSolutionsParameterName,
+                                                            "The percentage of the top solutions which should be analyzed.", new PercentValue(0.1)));
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (!Parameters.ContainsKey(PercentageOfBestSolutionsParameterName))
+        Parameters.Add(new ValueLookupParameter<PercentValue>(PercentageOfBestSolutionsParameterName,
+                                                               "The percentage of the top solutions which should be analyzed.", new PercentValue(1)));
+    }
+
+    protected IEnumerable<int> GenerateRowsToEvaluate() {
+      int seed = RandomParameter.ActualValue.Next();
+      int samplesStart = ValidationPartitionParameter.ActualValue.Start;
+      int samplesEnd = ValidationPartitionParameter.ActualValue.End;
+      int testPartitionStart = ProblemDataParameter.ActualValue.TestPartition.Start;
+      int testPartitionEnd = ProblemDataParameter.ActualValue.TestPartition.End;
+
+      if (samplesEnd < samplesStart) throw new ArgumentException("Start value is larger than end value.");
+      int count = (int)((samplesEnd - samplesStart) * RelativeNumberOfEvaluatedSamplesParameter.ActualValue.Value);
+      if (count == 0) count = 1;
+      return RandomEnumerable.SampleRandomNumbers(seed, samplesStart, samplesEnd, count)
+        .Where(i => i < testPartitionStart || testPartitionEnd <= i);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer.cs	(revision 16337)
@@ -0,0 +1,185 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// An operator that analyzes the validation best symbolic data analysis solution for single objective symbolic data analysis problems.
+  /// </summary>
+  [Item("SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer", "An operator that analyzes the validation best symbolic data analysis solution for single objective symbolic data analysis problems.")]
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer<S, T, U> : SymbolicDataAnalysisSingleObjectiveValidationAnalyzer<T, U>, IIterationBasedOperator
+    where S : class, ISymbolicDataAnalysisSolution
+    where T : class, ISymbolicDataAnalysisSingleObjectiveEvaluator<U>
+    where U : class, IDataAnalysisProblemData {
+    private const string ValidationBestSolutionParameterName = "Best validation solution";
+    private const string ValidationBestSolutionQualityParameterName = "Best validation solution quality";
+    private const string ValidationBestSolutionGenerationParameterName = "Best validation solution generation";
+    private const string UpdateAlwaysParameterName = "Always update best solution";
+    private const string IterationsParameterName = "Iterations";
+    private const string MaximumIterationsParameterName = "Maximum Iterations";
+
+    #region parameter properties
+    public ILookupParameter<S> ValidationBestSolutionParameter {
+      get { return (ILookupParameter<S>)Parameters[ValidationBestSolutionParameterName]; }
+    }
+    public ILookupParameter<DoubleValue> ValidationBestSolutionQualityParameter {
+      get { return (ILookupParameter<DoubleValue>)Parameters[ValidationBestSolutionQualityParameterName]; }
+    }
+    public ILookupParameter<IntValue> ValidationBestSolutionGenerationParameter {
+      get { return (ILookupParameter<IntValue>)Parameters[ValidationBestSolutionGenerationParameterName]; }
+    }
+    public IFixedValueParameter<BoolValue> UpdateAlwaysParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[UpdateAlwaysParameterName]; }
+    }
+    public ILookupParameter<IntValue> IterationsParameter {
+      get { return (ILookupParameter<IntValue>)Parameters[IterationsParameterName]; }
+    }
+    public IValueLookupParameter<IntValue> MaximumIterationsParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumIterationsParameterName]; }
+    }
+    #endregion
+    #region properties
+    public S ValidationBestSolution {
+      get { return ValidationBestSolutionParameter.ActualValue; }
+      set { ValidationBestSolutionParameter.ActualValue = value; }
+    }
+    public DoubleValue ValidationBestSolutionQuality {
+      get { return ValidationBestSolutionQualityParameter.ActualValue; }
+      set { ValidationBestSolutionQualityParameter.ActualValue = value; }
+    }
+    public BoolValue UpdateAlways {
+      get { return UpdateAlwaysParameter.Value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer(SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer<S, T, U> original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer()
+      : base() {
+      Parameters.Add(new LookupParameter<S>(ValidationBestSolutionParameterName, "The validation best symbolic data analyis solution."));
+      Parameters.Add(new LookupParameter<DoubleValue>(ValidationBestSolutionQualityParameterName, "The quality of the validation best symbolic data analysis solution."));
+      Parameters.Add(new LookupParameter<IntValue>(ValidationBestSolutionGenerationParameterName, "The generation in which the best validation solution was found."));
+      Parameters.Add(new FixedValueParameter<BoolValue>(UpdateAlwaysParameterName, "Determines if the best validation solution should always be updated regardless of its quality.", new BoolValue(false)));
+      Parameters.Add(new LookupParameter<IntValue>(IterationsParameterName, "The number of performed iterations."));
+      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumIterationsParameterName, "The maximum number of performed iterations.") { Hidden = true });
+      UpdateAlwaysParameter.Hidden = true;
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (!Parameters.ContainsKey(UpdateAlwaysParameterName)) {
+        Parameters.Add(new FixedValueParameter<BoolValue>(UpdateAlwaysParameterName, "Determines if the best validation solution should always be updated regardless of its quality.", new BoolValue(false)));
+        UpdateAlwaysParameter.Hidden = true;
+      }
+      if (!Parameters.ContainsKey(ValidationBestSolutionGenerationParameterName))
+        Parameters.Add(new LookupParameter<IntValue>(ValidationBestSolutionGenerationParameterName, "The generation in which the best validation solution was found."));
+      if (!Parameters.ContainsKey(IterationsParameterName))
+        Parameters.Add(new LookupParameter<IntValue>(IterationsParameterName, "The number of performed iterations."));
+      if (!Parameters.ContainsKey(MaximumIterationsParameterName))
+        Parameters.Add(new ValueLookupParameter<IntValue>(MaximumIterationsParameterName, "The maximum number of performed iterations.") { Hidden = true });
+    }
+
+    public override IOperation Apply() {
+      IEnumerable<int> rows = GenerateRowsToEvaluate();
+      if (!rows.Any()) return base.Apply();
+
+      #region find best tree
+      var evaluator = EvaluatorParameter.ActualValue;
+      var problemData = ProblemDataParameter.ActualValue;
+      double bestValidationQuality = Maximization.Value ? double.NegativeInfinity : double.PositiveInfinity;
+      ISymbolicExpressionTree bestTree = null;
+      ISymbolicExpressionTree[] tree = SymbolicExpressionTree.ToArray();
+
+      // sort is ascending and we take the first n% => order so that best solutions are smallest
+      // sort order is determined by maximization parameter
+      double[] trainingQuality;
+      if (Maximization.Value) {
+        // largest values must be sorted first
+        trainingQuality = Quality.Select(x => -x.Value).ToArray();
+      } else {
+        // smallest values must be sorted first
+        trainingQuality = Quality.Select(x => x.Value).ToArray();
+      }
+
+      // sort trees by training qualities
+      Array.Sort(trainingQuality, tree);
+
+      // number of best training solutions to validate (at least 1)
+      int topN = (int)Math.Max(tree.Length * PercentageOfBestSolutionsParameter.ActualValue.Value, 1);
+
+      IExecutionContext childContext = (IExecutionContext)ExecutionContext.CreateChildOperation(evaluator);
+      // evaluate best n training trees on validiation set
+      var quality = tree
+        .Take(topN)
+        .Select(t => evaluator.Evaluate(childContext, t, problemData, rows))
+        .ToArray();
+
+      for (int i = 0; i < quality.Length; i++) {
+        if (IsBetter(quality[i], bestValidationQuality, Maximization.Value)) {
+          bestValidationQuality = quality[i];
+          bestTree = tree[i];
+        }
+      }
+      #endregion
+
+      var results = ResultCollection;
+      if (UpdateAlways.Value || ValidationBestSolutionQuality == null ||
+        IsBetter(bestValidationQuality, ValidationBestSolutionQuality.Value, Maximization.Value)) {
+        ValidationBestSolution = CreateSolution(bestTree, bestValidationQuality);
+        ValidationBestSolutionQuality = new DoubleValue(bestValidationQuality);
+        if (IterationsParameter.ActualValue != null)
+          ValidationBestSolutionGenerationParameter.ActualValue = new IntValue(IterationsParameter.ActualValue.Value);
+
+        if (!results.ContainsKey(ValidationBestSolutionParameter.Name)) {
+          results.Add(new Result(ValidationBestSolutionParameter.Name, ValidationBestSolutionParameter.Description, ValidationBestSolution));
+          results.Add(new Result(ValidationBestSolutionQualityParameter.Name, ValidationBestSolutionQualityParameter.Description, ValidationBestSolutionQuality));
+          if (ValidationBestSolutionGenerationParameter.ActualValue != null)
+            results.Add(new Result(ValidationBestSolutionGenerationParameter.Name, ValidationBestSolutionGenerationParameter.Description, ValidationBestSolutionGenerationParameter.ActualValue));
+        } else {
+          results[ValidationBestSolutionParameter.Name].Value = ValidationBestSolution;
+          results[ValidationBestSolutionQualityParameter.Name].Value = ValidationBestSolutionQuality;
+          if (ValidationBestSolutionGenerationParameter.ActualValue != null)
+            results[ValidationBestSolutionGenerationParameter.Name].Value = ValidationBestSolutionGenerationParameter.ActualValue;
+        }
+      }
+      return base.Apply();
+    }
+
+    protected abstract S CreateSolution(ISymbolicExpressionTree bestTree, double bestQuality);
+
+    private bool IsBetter(double lhs, double rhs, bool maximization) {
+      if (maximization) return lhs > rhs;
+      else return lhs < rhs;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer.cs	(revision 16337)
@@ -0,0 +1,218 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// An operator that collects the Pareto-best symbolic data analysis solutions for single objective symbolic data analysis problems.
+  /// </summary>
+  [Item("SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer", "An operator that analyzes the Pareto-best symbolic data analysis solution for single objective symbolic data analysis problems.")]
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer<S, T, U> : SymbolicDataAnalysisSingleObjectiveValidationAnalyzer<T, U>, ISymbolicDataAnalysisBoundedOperator
+    where S : class, ISymbolicDataAnalysisSolution
+    where T : class, ISymbolicDataAnalysisSingleObjectiveEvaluator<U>
+    where U : class, IDataAnalysisProblemData {
+    private const string ValidationBestSolutionsParameterName = "Best validation solutions";
+    private const string ValidationBestSolutionQualitiesParameterName = "Best validation solution qualities";
+    private const string ComplexityParameterName = "Complexity";
+    private const string EstimationLimitsParameterName = "EstimationLimits";
+
+    public override bool EnabledByDefault {
+      get { return false; }
+    }
+
+    #region parameter properties
+    public ILookupParameter<ItemList<S>> ValidationBestSolutionsParameter {
+      get { return (ILookupParameter<ItemList<S>>)Parameters[ValidationBestSolutionsParameterName]; }
+    }
+    public ILookupParameter<ItemList<DoubleArray>> ValidationBestSolutionQualitiesParameter {
+      get { return (ILookupParameter<ItemList<DoubleArray>>)Parameters[ValidationBestSolutionQualitiesParameterName]; }
+    }
+    public IScopeTreeLookupParameter<DoubleValue> ComplexityParameter {
+      get { return (IScopeTreeLookupParameter<DoubleValue>)Parameters[ComplexityParameterName]; }
+    }
+    public IValueLookupParameter<DoubleLimit> EstimationLimitsParameter {
+      get { return (IValueLookupParameter<DoubleLimit>)Parameters[EstimationLimitsParameterName]; }
+    }
+
+    #endregion
+    #region properties
+    public ItemList<S> ValidationBestSolutions {
+      get { return ValidationBestSolutionsParameter.ActualValue; }
+      set { ValidationBestSolutionsParameter.ActualValue = value; }
+    }
+    public ItemList<DoubleArray> ValidationBestSolutionQualities {
+      get { return ValidationBestSolutionQualitiesParameter.ActualValue; }
+      set { ValidationBestSolutionQualitiesParameter.ActualValue = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer(SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer<S, T, U> original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer()
+      : base() {
+      Parameters.Add(new LookupParameter<ItemList<S>>(ValidationBestSolutionsParameterName, "The validation best (Pareto-optimal) symbolic data analysis solutions."));
+      Parameters.Add(new LookupParameter<ItemList<DoubleArray>>(ValidationBestSolutionQualitiesParameterName, "The qualities of the validation best (Pareto-optimal) solutions."));
+      Parameters.Add(new ScopeTreeLookupParameter<DoubleValue>(ComplexityParameterName, "The complexity of each tree."));
+      Parameters.Add(new ValueLookupParameter<DoubleLimit>(EstimationLimitsParameterName, "The lower and upper limit for the estimated values produced by the symbolic classification model."));
+    }
+
+    public override IOperation Apply() {
+      IEnumerable<int> rows = GenerateRowsToEvaluate();
+      if (!rows.Any()) return base.Apply();
+
+      #region find best tree
+      var evaluator = EvaluatorParameter.ActualValue;
+      var problemData = ProblemDataParameter.ActualValue;
+      ISymbolicExpressionTree[] tree = SymbolicExpressionTree.ToArray();
+
+      // sort is ascending and we take the first n% => order so that best solutions are smallest
+      // sort order is determined by maximization parameter
+      double[] trainingQuality;
+      if (Maximization.Value) {
+        // largest values must be sorted first
+        trainingQuality = Quality.Select(x => -x.Value).ToArray();
+      } else {
+        // smallest values must be sorted first
+        trainingQuality = Quality.Select(x => x.Value).ToArray();
+      }
+
+      int[] treeIndexes = Enumerable.Range(0, tree.Length).ToArray();
+
+      // sort trees by training qualities
+      Array.Sort(trainingQuality, treeIndexes);
+
+      // number of best training solutions to validate (at least 1)
+      int topN = (int)Math.Max(tree.Length * PercentageOfBestSolutionsParameter.ActualValue.Value, 1);
+
+      IExecutionContext childContext = (IExecutionContext)ExecutionContext.CreateChildOperation(evaluator);
+      // evaluate best n training trees on validiation set
+      var qualities = treeIndexes
+        .Select(i => tree[i])
+        .Take(topN)
+        .Select(t => evaluator.Evaluate(childContext, t, problemData, rows))
+        .ToArray();
+      #endregion
+
+      var results = ResultCollection;
+      // create empty parameter and result values
+      if (ValidationBestSolutions == null) {
+        ValidationBestSolutions = new ItemList<S>();
+        ValidationBestSolutionQualities = new ItemList<DoubleArray>();
+        results.Add(new Result(ValidationBestSolutionQualitiesParameter.Name, ValidationBestSolutionQualitiesParameter.Description, ValidationBestSolutionQualities));
+        results.Add(new Result(ValidationBestSolutionsParameter.Name, ValidationBestSolutionsParameter.Description, ValidationBestSolutions));
+      }
+
+      IList<Tuple<double, double>> validationBestQualities = ValidationBestSolutionQualities
+        .Select(x => Tuple.Create(x[0], x[1]))
+        .ToList();
+
+      #region find best trees
+      IList<int> nonDominatedIndexes = new List<int>();
+
+      List<double> complexities;
+      if (ComplexityParameter.ActualValue != null && ComplexityParameter.ActualValue.Length == trainingQuality.Length) {
+        complexities = ComplexityParameter.ActualValue.Select(x => x.Value).ToList();
+      } else {
+        complexities = tree.Select(t => (double)t.Length).ToList();
+      }
+      List<Tuple<double, double>> fitness = new List<Tuple<double, double>>();
+      for (int i = 0; i < qualities.Length; i++)
+        fitness.Add(Tuple.Create(qualities[i], complexities[treeIndexes[i]]));
+
+      var maximization = Tuple.Create(Maximization.Value, false); // complexity must be minimized
+      List<Tuple<double, double>> newNonDominatedQualities = new List<Tuple<double, double>>();
+      for (int i = 0; i < fitness.Count; i++) {
+        if (IsNonDominated(fitness[i], validationBestQualities, maximization) &&
+          IsNonDominated(fitness[i], newNonDominatedQualities, maximization) &&
+          IsNonDominated(fitness[i], fitness.Skip(i + 1), maximization)) {
+          if (!newNonDominatedQualities.Contains(fitness[i])) {
+            newNonDominatedQualities.Add(fitness[i]);
+            nonDominatedIndexes.Add(i);
+          }
+        }
+      }
+      #endregion
+
+      #region update Pareto-optimal solution archive
+      if (nonDominatedIndexes.Count > 0) {
+        ItemList<DoubleArray> nonDominatedQualities = new ItemList<DoubleArray>();
+        ItemList<S> nonDominatedSolutions = new ItemList<S>();
+        // add all new non-dominated solutions to the archive
+        foreach (var index in nonDominatedIndexes) {
+          S solution = CreateSolution(tree[treeIndexes[index]]);
+          nonDominatedSolutions.Add(solution);
+          nonDominatedQualities.Add(new DoubleArray(new double[] { fitness[index].Item1, fitness[index].Item2 }));
+        }
+        // add old non-dominated solutions only if they are not dominated by one of the new solutions
+        for (int i = 0; i < validationBestQualities.Count; i++) {
+          if (IsNonDominated(validationBestQualities[i], newNonDominatedQualities, maximization)) {
+            if (!newNonDominatedQualities.Contains(validationBestQualities[i])) {
+              nonDominatedSolutions.Add(ValidationBestSolutions[i]);
+              nonDominatedQualities.Add(ValidationBestSolutionQualities[i]);
+            }
+          }
+        }
+
+        // make sure solutions and qualities are ordered in the results
+        var orderedIndexes =
+          nonDominatedSolutions.Select((s, i) => i).OrderBy(i => nonDominatedQualities[i][0]).ToArray();
+
+        var orderedNonDominatedSolutions = new ItemList<S>();
+        var orderedNonDominatedQualities = new ItemList<DoubleArray>();
+        foreach (var i in orderedIndexes) {
+          orderedNonDominatedQualities.Add(nonDominatedQualities[i]);
+          orderedNonDominatedSolutions.Add(nonDominatedSolutions[i]);
+        }
+
+        ValidationBestSolutions = orderedNonDominatedSolutions;
+        ValidationBestSolutionQualities = orderedNonDominatedQualities;
+
+        results[ValidationBestSolutionsParameter.Name].Value = orderedNonDominatedSolutions;
+        results[ValidationBestSolutionQualitiesParameter.Name].Value = orderedNonDominatedQualities;
+      }
+      #endregion
+      return base.Apply();
+    }
+
+    protected abstract S CreateSolution(ISymbolicExpressionTree bestTree);
+
+    private bool IsNonDominated(Tuple<double, double> point, IEnumerable<Tuple<double, double>> points, Tuple<bool, bool> maximization) {
+      return !points.Any(p => IsBetterOrEqual(p.Item1, point.Item1, maximization.Item1) &&
+                             IsBetterOrEqual(p.Item2, point.Item2, maximization.Item2));
+    }
+    private bool IsBetterOrEqual(double lhs, double rhs, bool maximization) {
+      if (maximization) return lhs >= rhs;
+      else return lhs <= rhs;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisVariableFrequencyAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisVariableFrequencyAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Analyzers/SymbolicDataAnalysisVariableFrequencyAnalyzer.cs	(revision 16337)
@@ -0,0 +1,235 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using HeuristicLab.Analysis;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Calculates the accumulated frequencies of variable-symbols over all trees in the population.
+  /// </summary>
+  [Item("SymbolicDataAnalysisVariableFrequencyAnalyzer", "Calculates the accumulated frequencies of variable-symbols over all trees in the population.")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisVariableFrequencyAnalyzer : SymbolicDataAnalysisAnalyzer {
+    private const string VariableFrequenciesParameterName = "VariableFrequencies";
+    private const string AggregateLaggedVariablesParameterName = "AggregateLaggedVariables";
+    private const string AggregateFactorVariablesParameterName = "AggregateFactorVariables";
+    private const string VariableImpactsParameterName = "VariableImpacts";
+
+    #region parameter properties
+    public ILookupParameter<DataTable> VariableFrequenciesParameter {
+      get { return (ILookupParameter<DataTable>)Parameters[VariableFrequenciesParameterName]; }
+    }
+    public ILookupParameter<DoubleMatrix> VariableImpactsParameter {
+      get { return (ILookupParameter<DoubleMatrix>)Parameters[VariableImpactsParameterName]; }
+    }
+    public IValueLookupParameter<BoolValue> AggregateLaggedVariablesParameter {
+      get { return (IValueLookupParameter<BoolValue>)Parameters[AggregateLaggedVariablesParameterName]; }
+    }
+    public IValueLookupParameter<BoolValue> AggregateFactorVariablesParameter {
+      get { return (IValueLookupParameter<BoolValue>)Parameters[AggregateFactorVariablesParameterName]; }
+    }
+    #endregion
+    #region properties
+    public BoolValue AggregateLaggedVariables {
+      get { return AggregateLaggedVariablesParameter.ActualValue; }
+      set { AggregateLaggedVariablesParameter.Value = value; }
+    }
+    public BoolValue AggregateFactorVariables {
+      get { return AggregateFactorVariablesParameter.ActualValue; }
+      set { AggregateFactorVariablesParameter.Value = value; }
+    }
+    #endregion
+    [StorableConstructor]
+    private SymbolicDataAnalysisVariableFrequencyAnalyzer(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisVariableFrequencyAnalyzer(SymbolicDataAnalysisVariableFrequencyAnalyzer original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisVariableFrequencyAnalyzer()
+      : base() {
+      Parameters.Add(new LookupParameter<DataTable>(VariableFrequenciesParameterName, "The relative variable reference frequencies aggregated over all trees in the population."));
+      Parameters.Add(new LookupParameter<DoubleMatrix>(VariableImpactsParameterName, "The relative variable relevance calculated as the average relative variable frequency over the whole run."));
+      Parameters.Add(new ValueLookupParameter<BoolValue>(AggregateLaggedVariablesParameterName, "Switch that determines whether all references to a variable should be aggregated regardless of time-offsets. Turn off to analyze all variable references with different time offsets separately.", new BoolValue(true)));
+      Parameters.Add(new ValueLookupParameter<BoolValue>(AggregateFactorVariablesParameterName, "Switch that determines whether all references to factor variables should be aggregated regardless of the value. Turn off to analyze all factor variable references with different values separately.", new BoolValue(true)));
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      // BackwardsCompatibility3.3
+      #region Backwards compatible code, remove with 3.4
+      if (!Parameters.ContainsKey(AggregateFactorVariablesParameterName)) {
+        Parameters.Add(new ValueLookupParameter<BoolValue>(AggregateFactorVariablesParameterName, "Switch that determines whether all references to factor variables should be aggregated regardless of the value. Turn off to analyze all factor variable references with different values separately.", new BoolValue(true)));
+      }
+      #endregion
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisVariableFrequencyAnalyzer(this, cloner);
+    }
+
+    public override IOperation Apply() {
+      ItemArray<ISymbolicExpressionTree> expressions = SymbolicExpressionTreeParameter.ActualValue;
+      ResultCollection results = ResultCollection;
+      DataTable datatable;
+      if (VariableFrequenciesParameter.ActualValue == null) {
+        datatable = new DataTable("Variable frequencies", "Relative frequency of variable references aggregated over the whole population.");
+        datatable.VisualProperties.XAxisTitle = "Generation";
+        datatable.VisualProperties.YAxisTitle = "Relative Variable Frequency";
+        VariableFrequenciesParameter.ActualValue = datatable;
+        results.Add(new Result("Variable frequencies", "Relative frequency of variable references aggregated over the whole population.", datatable));
+        results.Add(new Result("Variable impacts", "The relative variable relevance calculated as the average relative variable frequency over the whole run.", new DoubleMatrix()));
+      }
+
+      datatable = VariableFrequenciesParameter.ActualValue;
+      // all rows must have the same number of values so we can just take the first
+      int numberOfValues = datatable.Rows.Select(r => r.Values.Count).DefaultIfEmpty().First();
+
+      foreach (var pair in CalculateVariableFrequencies(expressions, AggregateLaggedVariables.Value, AggregateFactorVariables.Value)) {
+        if (!datatable.Rows.ContainsKey(pair.Key)) {
+          // initialize a new row for the variable and pad with zeros
+          DataRow row = new DataRow(pair.Key, "", Enumerable.Repeat(0.0, numberOfValues));
+          row.VisualProperties.StartIndexZero = true;
+          datatable.Rows.Add(row);
+        }
+        datatable.Rows[pair.Key].Values.Add(Math.Round(pair.Value, 3));
+      }
+
+      // add a zero for each data row that was not modified in the previous loop 
+      foreach (var row in datatable.Rows.Where(r => r.Values.Count != numberOfValues + 1))
+        row.Values.Add(0.0);
+
+      // update variable impacts matrix
+      var orderedImpacts = (from row in datatable.Rows
+                            select new { Name = row.Name, Impact = Math.Round(datatable.Rows[row.Name].Values.Average(), 3) })
+                           .OrderByDescending(p => p.Impact)
+                           .ToList();
+      var impacts = new DoubleMatrix();
+      var matrix = impacts as IStringConvertibleMatrix;
+      matrix.Rows = orderedImpacts.Count;
+      matrix.RowNames = orderedImpacts.Select(x => x.Name);
+      matrix.Columns = 1;
+      matrix.ColumnNames = new string[] { "Relative variable relevance" };
+      int i = 0;
+      foreach (var p in orderedImpacts) {
+        matrix.SetValue(p.Impact.ToString(), i++, 0);
+      }
+
+      VariableImpactsParameter.ActualValue = impacts;
+      results["Variable impacts"].Value = impacts;
+      return base.Apply();
+    }
+
+    public static IEnumerable<KeyValuePair<string, double>> CalculateVariableFrequencies(IEnumerable<ISymbolicExpressionTree> trees,
+      bool aggregateLaggedVariables = true, bool aggregateFactorVariables = true) {
+
+      var variableFrequencies = trees
+        .SelectMany(t => GetVariableReferences(t, aggregateLaggedVariables, aggregateFactorVariables))
+        .GroupBy(pair => pair.Key, pair => pair.Value)
+        .ToDictionary(g => g.Key, g => (double)g.Sum());
+
+      double totalNumberOfSymbols = variableFrequencies.Values.Sum();
+
+      foreach (var pair in variableFrequencies.OrderBy(p => p.Key, new NaturalStringComparer()))
+        yield return new KeyValuePair<string, double>(pair.Key, pair.Value / totalNumberOfSymbols);
+    }
+
+    private static IEnumerable<KeyValuePair<string, int>> GetVariableReferences(ISymbolicExpressionTree tree,
+      bool aggregateLaggedVariables = true, bool aggregateFactorVariables = true) {
+      Dictionary<string, int> references = new Dictionary<string, int>();
+      if (aggregateLaggedVariables) {
+        tree.Root.ForEachNodePrefix(node => {
+          if (node is IVariableTreeNode) {
+            var factorNode = node as BinaryFactorVariableTreeNode;
+            if (factorNode != null && !aggregateFactorVariables) {
+              IncReferenceCount(references, factorNode.VariableName + "=" + factorNode.VariableValue);
+            } else {
+              var varNode = node as IVariableTreeNode;
+              IncReferenceCount(references, varNode.VariableName);
+            }
+          }
+        });
+      } else {
+        GetVariableReferences(references, tree.Root, 0, aggregateFactorVariables);
+      }
+      return references;
+    }
+
+    private static void GetVariableReferences(Dictionary<string, int> references, ISymbolicExpressionTreeNode node, int currentLag, bool aggregateFactorVariables) {
+      if (node is IVariableTreeNode) {
+        var laggedVarTreeNode = node as LaggedVariableTreeNode;
+        var binFactorVariableTreeNode = node as BinaryFactorVariableTreeNode;
+        var varConditionTreeNode = node as VariableConditionTreeNode;
+        if (laggedVarTreeNode != null) {
+          IncReferenceCount(references, laggedVarTreeNode.VariableName, currentLag + laggedVarTreeNode.Lag);
+        } else if (binFactorVariableTreeNode != null) {
+          if (aggregateFactorVariables) {
+            IncReferenceCount(references, binFactorVariableTreeNode.VariableName, currentLag);
+          } else {
+            IncReferenceCount(references, binFactorVariableTreeNode.VariableName + "=" + binFactorVariableTreeNode.VariableValue, currentLag);
+          }
+        } else if (varConditionTreeNode != null) {
+          IncReferenceCount(references, varConditionTreeNode.VariableName, currentLag);
+          GetVariableReferences(references, node.GetSubtree(0), currentLag, aggregateFactorVariables);
+          GetVariableReferences(references, node.GetSubtree(1), currentLag, aggregateFactorVariables);
+        } else {
+          var varNode = node as IVariableTreeNode;
+          IncReferenceCount(references, varNode.VariableName, currentLag);
+        }
+      } else if (node.Symbol is Integral) {
+        var laggedNode = node as LaggedTreeNode;
+        for (int l = laggedNode.Lag; l <= 0; l++) {
+          GetVariableReferences(references, node.GetSubtree(0), currentLag + l, aggregateFactorVariables);
+        }
+      } else if (node.Symbol is Derivative) {
+        for (int l = -4; l <= 0; l++) {
+          GetVariableReferences(references, node.GetSubtree(0), currentLag + l, aggregateFactorVariables);
+        }
+      } else if (node.Symbol is TimeLag) {
+        var laggedNode = node as LaggedTreeNode;
+        GetVariableReferences(references, node.GetSubtree(0), currentLag + laggedNode.Lag, aggregateFactorVariables);
+      } else {
+        foreach (var subtree in node.Subtrees) {
+          GetVariableReferences(references, subtree, currentLag, aggregateFactorVariables);
+        }
+      }
+    }
+
+    private static void IncReferenceCount(Dictionary<string, int> references, string variableName, int timeLag = 0) {
+      string referenceId = variableName +
+        (timeLag == 0 ? "" : timeLag < 0 ? "(t" + timeLag + ")" : "(t+" + timeLag + ")");
+      if (references.ContainsKey(referenceId)) {
+        references[referenceId]++;
+      } else {
+        references[referenceId] = 1;
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/DerivativeCalculator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/DerivativeCalculator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/DerivativeCalculator.cs	(revision 16337)
@@ -0,0 +1,231 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class DerivativeCalculator {
+    public static ISymbolicExpressionTree Derive(ISymbolicExpressionTree tree, string variableName) {
+      if (tree.Root.SubtreeCount != 1)
+        throw new NotImplementedException("Derive is not implemented for symbolic expressions with automatically defined functions (ADF)");
+      if (tree.Root.GetSubtree(0).SubtreeCount != 1)
+        throw new NotImplementedException("Derive is not implemented for multi-variate symbolic expressions");
+      var mainBranch = tree.Root.GetSubtree(0).GetSubtree(0);
+      var root = new ProgramRootSymbol().CreateTreeNode();
+      root.AddSubtree(new StartSymbol().CreateTreeNode());
+      var dTree = TreeSimplifier.GetSimplifiedTree(Derive(mainBranch, variableName));
+      //var dTree = Derive(mainBranch, variableName);
+      root.GetSubtree(0).AddSubtree(dTree);
+      return new SymbolicExpressionTree(root);
+    }
+
+    private static readonly Constant constantSy = new Constant();
+    private static readonly Addition addSy = new Addition();
+    private static readonly Subtraction subSy = new Subtraction();
+    private static readonly Multiplication mulSy = new Multiplication();
+    private static readonly Division divSy = new Division();
+    private static readonly Cosine cosSy = new Cosine();
+    private static readonly Square sqrSy = new Square();
+
+    public static ISymbolicExpressionTreeNode Derive(ISymbolicExpressionTreeNode branch, string variableName) {
+      if (branch.Symbol is Constant) {
+        return CreateConstant(0.0);
+      }
+      if (branch.Symbol is Variable) {
+        var varNode = branch as VariableTreeNode;
+        if (varNode.VariableName == variableName) {
+          return CreateConstant(varNode.Weight);
+        } else {
+          return CreateConstant(0.0);
+        }
+      }
+      if (branch.Symbol is Addition) {
+        var sum = addSy.CreateTreeNode();
+        foreach (var subTree in branch.Subtrees) {
+          sum.AddSubtree(Derive(subTree, variableName));
+        }
+        return sum;
+      }
+      if (branch.Symbol is Subtraction) {
+        var sum = subSy.CreateTreeNode();
+        foreach (var subTree in branch.Subtrees) {
+          sum.AddSubtree(Derive(subTree, variableName));
+        }
+        return sum;
+      }
+      if (branch.Symbol is Multiplication) {
+        // (f * g)' = f'*g + f*g'
+        // for multiple factors: (f * g * h)' = ((f*g) * h)' = (f*g)' * h + (f*g) * h' 
+
+        if (branch.SubtreeCount >= 2) {
+          var f = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+          var g = (ISymbolicExpressionTreeNode)branch.GetSubtree(1).Clone();
+          var fprime = Derive(f, variableName);
+          var gprime = Derive(g, variableName);
+          var fgPrime = Sum(Product(f, gprime), Product(fprime, g));
+          for (int i = 2; i < branch.SubtreeCount; i++) {
+            var fg = Product((ISymbolicExpressionTreeNode)f.Clone(), (ISymbolicExpressionTreeNode)g.Clone());
+            var h = (ISymbolicExpressionTreeNode)branch.GetSubtree(i).Clone();
+            var hPrime = Derive(h, variableName);
+            fgPrime = Sum(Product(fgPrime, h), Product(fg, hPrime));
+          }
+          return fgPrime;
+        } else
+          // multiplication with only one argument has no effect -> derive the argument
+          return Derive(branch.GetSubtree(0), variableName);
+      }
+      if (branch.Symbol is Division) {
+        // (f/g)' = (f'g - g'f) / g²
+        if (branch.SubtreeCount == 1) {
+          var g = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+          var gPrime = Product(CreateConstant(-1.0), Derive(g, variableName));
+          var sqrNode = new Square().CreateTreeNode();
+          sqrNode.AddSubtree(g);
+          return Div(gPrime, sqrNode);
+        } else {
+          // for two subtrees:
+          // (f/g)' = (f'g - fg')/g²
+
+          // if there are more than 2 subtrees
+          // div(x,y,z) is interpretered as (x/y)/z
+          // which is the same as x / (y*z)
+
+          // --> make a product of all but the first subtree and differentiate as for the 2-argument case above
+          var f = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+          var g = Product(branch.Subtrees.Skip(1).Select(n => (ISymbolicExpressionTreeNode)n.Clone()));
+          var fprime = Derive(f, variableName);
+          var gprime = Derive(g, variableName);
+          var gSqr = Square(g);
+          return Div(Subtract(Product(fprime, g), Product(f, gprime)), gSqr);
+        }
+      }
+      if (branch.Symbol is Logarithm) {
+        var f = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+        return Product(Div(CreateConstant(1.0), f), Derive(f, variableName));
+      }
+      if (branch.Symbol is Exponential) {
+        var f = (ISymbolicExpressionTreeNode)branch.Clone();
+        return Product(f, Derive(branch.GetSubtree(0), variableName));
+      }
+      if (branch.Symbol is Square) {
+        var f = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+        return Product(Product(CreateConstant(2.0), f), Derive(f, variableName));
+      }
+      if (branch.Symbol is SquareRoot) {
+        var f = (ISymbolicExpressionTreeNode)branch.Clone();
+        var u = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+        return Product(Div(CreateConstant(1.0), Product(CreateConstant(2.0), f)), Derive(u, variableName));
+      }
+      if (branch.Symbol is Sine) {
+        var u = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+        var cos = (new Cosine()).CreateTreeNode();
+        cos.AddSubtree(u);
+        return Product(cos, Derive(u, variableName));
+      }
+      if (branch.Symbol is Cosine) {
+        var u = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+        var sin = (new Sine()).CreateTreeNode();
+        sin.AddSubtree(u);
+        return Product(CreateConstant(-1.0), Product(sin, Derive(u, variableName)));
+      }
+      if (branch.Symbol is Tangent) {
+        // tan(x)' = 1 / cos²(x)
+        var fxp = Derive(branch.GetSubtree(0), variableName);
+        var u = (ISymbolicExpressionTreeNode)branch.GetSubtree(0).Clone();
+        return Div(fxp, Square(Cosine(u)));
+      }
+      throw new NotSupportedException(string.Format("Symbol {0} is not supported.", branch.Symbol));
+    }
+
+
+    private static ISymbolicExpressionTreeNode Product(ISymbolicExpressionTreeNode f, ISymbolicExpressionTreeNode g) {
+      var product = mulSy.CreateTreeNode();
+      product.AddSubtree(f);
+      product.AddSubtree(g);
+      return product;
+    }
+    private static ISymbolicExpressionTreeNode Product(IEnumerable<ISymbolicExpressionTreeNode> fs) {
+      var product = mulSy.CreateTreeNode();
+      foreach (var f in fs) product.AddSubtree(f);
+      return product;
+    }
+    private static ISymbolicExpressionTreeNode Div(ISymbolicExpressionTreeNode f, ISymbolicExpressionTreeNode g) {
+      var div = divSy.CreateTreeNode();
+      div.AddSubtree(f);
+      div.AddSubtree(g);
+      return div;
+    }
+
+    private static ISymbolicExpressionTreeNode Sum(ISymbolicExpressionTreeNode f, ISymbolicExpressionTreeNode g) {
+      var sum = addSy.CreateTreeNode();
+      sum.AddSubtree(f);
+      sum.AddSubtree(g);
+      return sum;
+    }
+    private static ISymbolicExpressionTreeNode Subtract(ISymbolicExpressionTreeNode f, ISymbolicExpressionTreeNode g) {
+      var sum = subSy.CreateTreeNode();
+      sum.AddSubtree(f);
+      sum.AddSubtree(g);
+      return sum;
+    }
+    private static ISymbolicExpressionTreeNode Cosine(ISymbolicExpressionTreeNode f) {
+      var cos = cosSy.CreateTreeNode();
+      cos.AddSubtree(f);
+      return cos;
+    }
+    private static ISymbolicExpressionTreeNode Square(ISymbolicExpressionTreeNode f) {
+      var sqr = sqrSy.CreateTreeNode();
+      sqr.AddSubtree(f);
+      return sqr;
+    }
+
+    private static ISymbolicExpressionTreeNode CreateConstant(double v) {
+      var constNode = (ConstantTreeNode)constantSy.CreateTreeNode();
+      constNode.Value = v;
+      return constNode;
+    }
+
+    public static bool IsCompatible(ISymbolicExpressionTree tree) {
+      var containsUnknownSymbol = (
+        from n in tree.Root.GetSubtree(0).IterateNodesPrefix()
+        where
+          !(n.Symbol is Variable) &&
+          !(n.Symbol is Constant) &&
+          !(n.Symbol is Addition) &&
+          !(n.Symbol is Subtraction) &&
+          !(n.Symbol is Multiplication) &&
+          !(n.Symbol is Division) &&
+          !(n.Symbol is Logarithm) &&
+          !(n.Symbol is Exponential) &&
+          !(n.Symbol is Square) &&
+          !(n.Symbol is SquareRoot) &&
+          !(n.Symbol is Sine) &&
+          !(n.Symbol is Cosine) &&
+          !(n.Symbol is Tangent) &&
+          !(n.Symbol is StartSymbol)
+        select n).Any();
+      return !containsUnknownSymbol;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/LinearModelToTreeConverter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/LinearModelToTreeConverter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/LinearModelToTreeConverter.cs	(revision 16337)
@@ -0,0 +1,132 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class LinearModelToTreeConverter {
+    public static ISymbolicExpressionTree CreateTree(string[] variableNames, double[] coefficients,
+      double @const = 0) {
+      return CreateTree(variableNames, new int[variableNames.Length], coefficients, @const);
+    }
+
+    public static ISymbolicExpressionTree CreateTree(
+      IEnumerable<KeyValuePair<string, IEnumerable<string>>> factors, double[] factorCoefficients,
+      string[] variableNames, double[] coefficients,
+      double @const = 0) {
+
+      if (factorCoefficients.Length == 0 && coefficients.Length == 0) throw new ArgumentException();
+
+      // Create tree for double variables
+      ISymbolicExpressionTree tree = null;      
+      if (coefficients.Length > 0) {
+        tree = CreateTree(variableNames, new int[variableNames.Length], coefficients, @const);
+        if (factorCoefficients.Length == 0) return tree;
+      }
+
+      // Create tree for string variables
+      ISymbolicExpressionTree factorTree = null;      
+      if (factorCoefficients.Length > 0) {
+        factorTree = CreateTree(factors, factorCoefficients, @const);
+        if (tree == null) return factorTree;  
+      }
+
+      // Combine both trees
+      ISymbolicExpressionTreeNode add = tree.Root.GetSubtree(0).GetSubtree(0);
+      foreach (var binFactorNode in factorTree.IterateNodesPrefix().OfType<BinaryFactorVariableTreeNode>())
+        add.InsertSubtree(add.SubtreeCount - 1, binFactorNode);
+      return tree;
+
+      throw new ArgumentException();
+    }
+
+    public static ISymbolicExpressionTree CreateTree(string[] variableNames, int[] lags, double[] coefficients,
+      double @const = 0) {
+      if (variableNames.Length == 0 ||
+        variableNames.Length != coefficients.Length ||
+        variableNames.Length != lags.Length)
+        throw new ArgumentException("The length of the variable names, lags, and coefficients vectors must match");
+
+      ISymbolicExpressionTree tree = new SymbolicExpressionTree(new ProgramRootSymbol().CreateTreeNode());
+      ISymbolicExpressionTreeNode startNode = new StartSymbol().CreateTreeNode();
+      tree.Root.AddSubtree(startNode);
+      ISymbolicExpressionTreeNode addition = new Addition().CreateTreeNode();
+      startNode.AddSubtree(addition);
+
+      for (int i = 0; i < variableNames.Length; i++) {
+        if (lags[i] == 0) {
+          VariableTreeNode vNode = (VariableTreeNode)new Variable().CreateTreeNode();
+          vNode.VariableName = variableNames[i];
+          vNode.Weight = coefficients[i];
+          addition.AddSubtree(vNode);
+        } else {
+          LaggedVariableTreeNode vNode = (LaggedVariableTreeNode)new LaggedVariable().CreateTreeNode();
+          vNode.VariableName = variableNames[i];
+          vNode.Weight = coefficients[i];
+          vNode.Lag = lags[i];
+          addition.AddSubtree(vNode);
+        }
+      }
+
+      if (!@const.IsAlmost(0.0)) {
+        ConstantTreeNode cNode = (ConstantTreeNode)new Constant().CreateTreeNode();
+        cNode.Value = @const;
+        addition.AddSubtree(cNode);
+      }
+      return tree;
+    }
+
+    public static ISymbolicExpressionTree CreateTree(IEnumerable<KeyValuePair<string, IEnumerable<string>>> factors,
+      double[] factorCoefficients,
+      double @const = 0) {
+
+      ISymbolicExpressionTree tree = new SymbolicExpressionTree(new ProgramRootSymbol().CreateTreeNode());
+      ISymbolicExpressionTreeNode startNode = new StartSymbol().CreateTreeNode();
+      tree.Root.AddSubtree(startNode);
+      ISymbolicExpressionTreeNode addition = new Addition().CreateTreeNode();
+      startNode.AddSubtree(addition);
+
+      int i = 0;
+      foreach (var factor in factors) {
+        var varName = factor.Key;
+        foreach (var factorValue in factor.Value) {
+          var node = (BinaryFactorVariableTreeNode)new BinaryFactorVariable().CreateTreeNode();
+          node.VariableValue = factorValue;
+          node.VariableName = varName;
+          node.Weight = factorCoefficients[i];
+          addition.AddSubtree(node);
+          i++;
+        }
+      }
+
+      if (!@const.IsAlmost(0.0)) {
+        ConstantTreeNode cNode = (ConstantTreeNode)new Constant().CreateTreeNode();
+        cNode.Value = @const;
+        addition.AddSubtree(cNode);
+      }
+      return tree;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/TreeSimplifier.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/TreeSimplifier.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/TreeSimplifier.cs	(revision 16337)
@@ -0,0 +1,1342 @@
+﻿#region License Information
+
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Simplifier for symbolic expressions
+  /// </summary>
+  public class TreeSimplifier {
+    private static readonly Addition addSymbol = new Addition();
+    private static readonly Multiplication mulSymbol = new Multiplication();
+    private static readonly Division divSymbol = new Division();
+    private static readonly Constant constSymbol = new Constant();
+    private static readonly Logarithm logSymbol = new Logarithm();
+    private static readonly Exponential expSymbol = new Exponential();
+    private static readonly Root rootSymbol = new Root();
+    private static readonly Square sqrSymbol = new Square();
+    private static readonly SquareRoot sqrtSymbol = new SquareRoot();
+    private static readonly Power powSymbol = new Power();
+    private static readonly Sine sineSymbol = new Sine();
+    private static readonly Cosine cosineSymbol = new Cosine();
+    private static readonly Tangent tanSymbol = new Tangent();
+    private static readonly IfThenElse ifThenElseSymbol = new IfThenElse();
+    private static readonly And andSymbol = new And();
+    private static readonly Or orSymbol = new Or();
+    private static readonly Not notSymbol = new Not();
+    private static readonly GreaterThan gtSymbol = new GreaterThan();
+    private static readonly LessThan ltSymbol = new LessThan();
+    private static readonly Integral integralSymbol = new Integral();
+    private static readonly LaggedVariable laggedVariableSymbol = new LaggedVariable();
+    private static readonly TimeLag timeLagSymbol = new TimeLag();
+
+    [Obsolete("Use static method TreeSimplifier.Simplify instead")]
+    public TreeSimplifier() { }
+
+    public static ISymbolicExpressionTree Simplify(ISymbolicExpressionTree originalTree) {
+      var clone = (ISymbolicExpressionTreeNode)originalTree.Root.Clone();
+      // macro expand (initially no argument trees)
+      var macroExpandedTree = MacroExpand(clone, clone.GetSubtree(0), new List<ISymbolicExpressionTreeNode>());
+      ISymbolicExpressionTreeNode rootNode = (new ProgramRootSymbol()).CreateTreeNode();
+      rootNode.AddSubtree(GetSimplifiedTree(macroExpandedTree));
+
+#if DEBUG
+      // check that each node is only referenced once
+      var nodes = rootNode.IterateNodesPrefix().ToArray();
+      foreach (var n in nodes) if (nodes.Count(ni => ni == n) > 1) throw new InvalidOperationException();
+#endif
+      return new SymbolicExpressionTree(rootNode);
+    }
+
+    // the argumentTrees list contains already expanded trees used as arguments for invocations
+    private static ISymbolicExpressionTreeNode MacroExpand(ISymbolicExpressionTreeNode root, ISymbolicExpressionTreeNode node,
+      IList<ISymbolicExpressionTreeNode> argumentTrees) {
+      List<ISymbolicExpressionTreeNode> subtrees = new List<ISymbolicExpressionTreeNode>(node.Subtrees);
+      while (node.SubtreeCount > 0) node.RemoveSubtree(0);
+      if (node.Symbol is InvokeFunction) {
+        var invokeSym = node.Symbol as InvokeFunction;
+        var defunNode = FindFunctionDefinition(root, invokeSym.FunctionName);
+        var macroExpandedArguments = new List<ISymbolicExpressionTreeNode>();
+        foreach (var subtree in subtrees) {
+          macroExpandedArguments.Add(MacroExpand(root, subtree, argumentTrees));
+        }
+        return MacroExpand(root, defunNode, macroExpandedArguments);
+      } else if (node.Symbol is Argument) {
+        var argSym = node.Symbol as Argument;
+        // return the correct argument sub-tree (already macro-expanded)
+        return (SymbolicExpressionTreeNode)argumentTrees[argSym.ArgumentIndex].Clone();
+      } else {
+        // recursive application
+        foreach (var subtree in subtrees) {
+          node.AddSubtree(MacroExpand(root, subtree, argumentTrees));
+        }
+        return node;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode FindFunctionDefinition(ISymbolicExpressionTreeNode root, string functionName) {
+      foreach (var subtree in root.Subtrees.OfType<DefunTreeNode>()) {
+        if (subtree.FunctionName == functionName) return subtree.GetSubtree(0);
+      }
+
+      throw new ArgumentException("Definition of function " + functionName + " not found.");
+    }
+
+    #region symbol predicates
+
+    // arithmetic
+    private static bool IsDivision(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Division;
+    }
+
+    private static bool IsMultiplication(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Multiplication;
+    }
+
+    private static bool IsSubtraction(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Subtraction;
+    }
+
+    private static bool IsAddition(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Addition;
+    }
+
+    private static bool IsAverage(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Average;
+    }
+
+    // exponential
+    private static bool IsLog(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Logarithm;
+    }
+
+    private static bool IsExp(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Exponential;
+    }
+
+    private static bool IsRoot(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Root;
+    }
+
+    private static bool IsSquare(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Square;
+    }
+
+    private static bool IsSquareRoot(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is SquareRoot;
+    }
+
+    private static bool IsPower(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Power;
+    }
+
+    // trigonometric
+    private static bool IsSine(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Sine;
+    }
+
+    private static bool IsCosine(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Cosine;
+    }
+
+    private static bool IsTangent(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Tangent;
+    }
+
+    // boolean
+    private static bool IsIfThenElse(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is IfThenElse;
+    }
+
+    private static bool IsAnd(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is And;
+    }
+
+    private static bool IsOr(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Or;
+    }
+
+    private static bool IsNot(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Not;
+    }
+
+    // comparison
+    private static bool IsGreaterThan(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is GreaterThan;
+    }
+
+    private static bool IsLessThan(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is LessThan;
+    }
+
+    private static bool IsBoolean(ISymbolicExpressionTreeNode node) {
+      return
+        node.Symbol is GreaterThan ||
+        node.Symbol is LessThan ||
+        node.Symbol is And ||
+        node.Symbol is Or;
+    }
+
+    // terminals
+    private static bool IsVariable(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Variable;
+    }
+
+    private static bool IsVariableBase(ISymbolicExpressionTreeNode node) {
+      return node is VariableTreeNodeBase;
+    }
+
+    private static bool IsFactor(ISymbolicExpressionTreeNode node) {
+      return node is FactorVariableTreeNode;
+    }
+
+    private static bool IsBinFactor(ISymbolicExpressionTreeNode node) {
+      return node is BinaryFactorVariableTreeNode;
+    }
+
+    private static bool IsConstant(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Constant;
+    }
+
+    // dynamic
+    private static bool IsTimeLag(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is TimeLag;
+    }
+
+    private static bool IsIntegral(ISymbolicExpressionTreeNode node) {
+      return node.Symbol is Integral;
+    }
+
+    #endregion
+
+    /// <summary>
+    /// Creates a new simplified tree
+    /// </summary>
+    /// <param name="original"></param>
+    /// <returns></returns>
+    public static ISymbolicExpressionTreeNode GetSimplifiedTree(ISymbolicExpressionTreeNode original) {
+      if (IsConstant(original) || IsVariableBase(original)) {
+        return (ISymbolicExpressionTreeNode)original.Clone();
+      } else if (IsAddition(original)) {
+        return SimplifyAddition(original);
+      } else if (IsSubtraction(original)) {
+        return SimplifySubtraction(original);
+      } else if (IsMultiplication(original)) {
+        return SimplifyMultiplication(original);
+      } else if (IsDivision(original)) {
+        return SimplifyDivision(original);
+      } else if (IsAverage(original)) {
+        return SimplifyAverage(original);
+      } else if (IsLog(original)) {
+        return SimplifyLog(original);
+      } else if (IsExp(original)) {
+        return SimplifyExp(original);
+      } else if (IsSquare(original)) {
+        return SimplifySquare(original);
+      } else if (IsSquareRoot(original)) {
+        return SimplifySquareRoot(original);
+      } else if (IsPower(original)) {
+        return SimplifyPower(original);
+      } else if (IsRoot(original)) {
+        return SimplifyRoot(original);
+      } else if (IsSine(original)) {
+        return SimplifySine(original);
+      } else if (IsCosine(original)) {
+        return SimplifyCosine(original);
+      } else if (IsTangent(original)) {
+        return SimplifyTangent(original);
+      } else if (IsIfThenElse(original)) {
+        return SimplifyIfThenElse(original);
+      } else if (IsGreaterThan(original)) {
+        return SimplifyGreaterThan(original);
+      } else if (IsLessThan(original)) {
+        return SimplifyLessThan(original);
+      } else if (IsAnd(original)) {
+        return SimplifyAnd(original);
+      } else if (IsOr(original)) {
+        return SimplifyOr(original);
+      } else if (IsNot(original)) {
+        return SimplifyNot(original);
+      } else if (IsTimeLag(original)) {
+        return SimplifyTimeLag(original);
+      } else if (IsIntegral(original)) {
+        return SimplifyIntegral(original);
+      } else {
+        return SimplifyAny(original);
+      }
+    }
+
+    #region specific simplification routines
+
+    private static ISymbolicExpressionTreeNode SimplifyAny(ISymbolicExpressionTreeNode original) {
+      // can't simplify this function but simplify all subtrees 
+      List<ISymbolicExpressionTreeNode> subtrees = new List<ISymbolicExpressionTreeNode>(original.Subtrees);
+      while (original.Subtrees.Count() > 0) original.RemoveSubtree(0);
+      var clone = (SymbolicExpressionTreeNode)original.Clone();
+      List<ISymbolicExpressionTreeNode> simplifiedSubtrees = new List<ISymbolicExpressionTreeNode>();
+      foreach (var subtree in subtrees) {
+        simplifiedSubtrees.Add(GetSimplifiedTree(subtree));
+        original.AddSubtree(subtree);
+      }
+      foreach (var simplifiedSubtree in simplifiedSubtrees) {
+        clone.AddSubtree(simplifiedSubtree);
+      }
+      if (simplifiedSubtrees.TrueForAll(t => IsConstant(t))) {
+        SimplifyConstantExpression(clone);
+      }
+      return clone;
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyConstantExpression(ISymbolicExpressionTreeNode original) {
+      // not yet implemented
+      return original;
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyAverage(ISymbolicExpressionTreeNode original) {
+      if (original.Subtrees.Count() == 1) {
+        return GetSimplifiedTree(original.GetSubtree(0));
+      } else {
+        // simplify expressions x0..xn
+        // make sum(x0..xn) / n
+        var sum = original.Subtrees
+          .Select(GetSimplifiedTree)
+          .Aggregate(MakeSum);
+        return MakeFraction(sum, MakeConstant(original.Subtrees.Count()));
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyDivision(ISymbolicExpressionTreeNode original) {
+      if (original.Subtrees.Count() == 1) {
+        return Invert(GetSimplifiedTree(original.GetSubtree(0)));
+      } else {
+        // simplify expressions x0..xn
+        // make multiplication (x0 * 1/(x1 * x1 * .. * xn))
+        var first = original.GetSubtree(0);
+        var second = original.GetSubtree(1);
+        var remaining = original.Subtrees.Skip(2);
+        return
+          MakeProduct(GetSimplifiedTree(first),
+            Invert(remaining.Aggregate(GetSimplifiedTree(second), (a, b) => MakeProduct(a, GetSimplifiedTree(b)))));
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyMultiplication(ISymbolicExpressionTreeNode original) {
+      if (original.Subtrees.Count() == 1) {
+        return GetSimplifiedTree(original.GetSubtree(0));
+      } else {
+        return original.Subtrees
+          .Select(GetSimplifiedTree)
+          .Aggregate(MakeProduct);
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifySubtraction(ISymbolicExpressionTreeNode original) {
+      if (original.Subtrees.Count() == 1) {
+        return Negate(GetSimplifiedTree(original.GetSubtree(0)));
+      } else {
+        // simplify expressions x0..xn
+        // make addition (x0,-x1..-xn)
+        var first = original.Subtrees.First();
+        var remaining = original.Subtrees.Skip(1);
+        return remaining.Aggregate(GetSimplifiedTree(first), (a, b) => MakeSum(a, Negate(GetSimplifiedTree(b))));
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyAddition(ISymbolicExpressionTreeNode original) {
+      if (original.Subtrees.Count() == 1) {
+        return GetSimplifiedTree(original.GetSubtree(0));
+      } else {
+        // simplify expression x0..xn
+        // make addition (x0..xn)
+        return original.Subtrees
+          .Select(GetSimplifiedTree)
+          .Aggregate(MakeSum);
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyNot(ISymbolicExpressionTreeNode original) {
+      return MakeNot(GetSimplifiedTree(original.GetSubtree(0)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyOr(ISymbolicExpressionTreeNode original) {
+      return original.Subtrees
+        .Select(GetSimplifiedTree)
+        .Aggregate(MakeOr);
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyAnd(ISymbolicExpressionTreeNode original) {
+      return original.Subtrees
+        .Select(GetSimplifiedTree)
+        .Aggregate(MakeAnd);
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyLessThan(ISymbolicExpressionTreeNode original) {
+      return MakeLessThan(GetSimplifiedTree(original.GetSubtree(0)), GetSimplifiedTree(original.GetSubtree(1)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyGreaterThan(ISymbolicExpressionTreeNode original) {
+      return MakeGreaterThan(GetSimplifiedTree(original.GetSubtree(0)), GetSimplifiedTree(original.GetSubtree(1)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyIfThenElse(ISymbolicExpressionTreeNode original) {
+      return MakeIfThenElse(GetSimplifiedTree(original.GetSubtree(0)), GetSimplifiedTree(original.GetSubtree(1)),
+        GetSimplifiedTree(original.GetSubtree(2)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyTangent(ISymbolicExpressionTreeNode original) {
+      return MakeTangent(GetSimplifiedTree(original.GetSubtree(0)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyCosine(ISymbolicExpressionTreeNode original) {
+      return MakeCosine(GetSimplifiedTree(original.GetSubtree(0)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifySine(ISymbolicExpressionTreeNode original) {
+      return MakeSine(GetSimplifiedTree(original.GetSubtree(0)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyExp(ISymbolicExpressionTreeNode original) {
+      return MakeExp(GetSimplifiedTree(original.GetSubtree(0)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifySquare(ISymbolicExpressionTreeNode original) {
+      return MakeSquare(GetSimplifiedTree(original.GetSubtree(0)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifySquareRoot(ISymbolicExpressionTreeNode original) {
+      return MakeSquareRoot(GetSimplifiedTree(original.GetSubtree(0)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyLog(ISymbolicExpressionTreeNode original) {
+      return MakeLog(GetSimplifiedTree(original.GetSubtree(0)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyRoot(ISymbolicExpressionTreeNode original) {
+      return MakeRoot(GetSimplifiedTree(original.GetSubtree(0)), GetSimplifiedTree(original.GetSubtree(1)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyPower(ISymbolicExpressionTreeNode original) {
+      return MakePower(GetSimplifiedTree(original.GetSubtree(0)), GetSimplifiedTree(original.GetSubtree(1)));
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyTimeLag(ISymbolicExpressionTreeNode original) {
+      var laggedTreeNode = original as ILaggedTreeNode;
+      var simplifiedSubtree = GetSimplifiedTree(original.GetSubtree(0));
+      if (!ContainsVariableCondition(simplifiedSubtree)) {
+        return AddLagToDynamicNodes(simplifiedSubtree, laggedTreeNode.Lag);
+      } else {
+        return MakeTimeLag(simplifiedSubtree, laggedTreeNode.Lag);
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode SimplifyIntegral(ISymbolicExpressionTreeNode original) {
+      var laggedTreeNode = original as ILaggedTreeNode;
+      var simplifiedSubtree = GetSimplifiedTree(original.GetSubtree(0));
+      if (IsConstant(simplifiedSubtree)) {
+        return GetSimplifiedTree(MakeProduct(simplifiedSubtree, MakeConstant(-laggedTreeNode.Lag)));
+      } else {
+        return MakeIntegral(simplifiedSubtree, laggedTreeNode.Lag);
+      }
+    }
+
+    #endregion
+
+    #region low level tree restructuring
+
+    private static ISymbolicExpressionTreeNode MakeTimeLag(ISymbolicExpressionTreeNode subtree, int lag) {
+      if (lag == 0) return subtree;
+      if (IsConstant(subtree)) return subtree;
+      var lagNode = (LaggedTreeNode)timeLagSymbol.CreateTreeNode();
+      lagNode.Lag = lag;
+      lagNode.AddSubtree(subtree);
+      return lagNode;
+    }
+
+    private static ISymbolicExpressionTreeNode MakeIntegral(ISymbolicExpressionTreeNode subtree, int lag) {
+      if (lag == 0) return subtree;
+      else if (lag == -1 || lag == 1) {
+        return MakeSum(subtree, AddLagToDynamicNodes((ISymbolicExpressionTreeNode)subtree.Clone(), lag));
+      } else {
+        var node = (LaggedTreeNode)integralSymbol.CreateTreeNode();
+        node.Lag = lag;
+        node.AddSubtree(subtree);
+        return node;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeNot(ISymbolicExpressionTreeNode t) {
+      if (IsConstant(t)) {
+        var constNode = t as ConstantTreeNode;
+        if (constNode.Value > 0) return MakeConstant(-1.0);
+        else return MakeConstant(1.0);
+      } else if (IsNot(t)) {
+        return t.GetSubtree(0);
+      } else if (!IsBoolean(t)) {
+        var gtNode = gtSymbol.CreateTreeNode();
+        gtNode.AddSubtree(t);
+        gtNode.AddSubtree(MakeConstant(0.0));
+        var notNode = notSymbol.CreateTreeNode();
+        notNode.AddSubtree(gtNode);
+        return notNode;
+      } else {
+        var notNode = notSymbol.CreateTreeNode();
+        notNode.AddSubtree(t);
+        return notNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeOr(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      if (IsConstant(a) && IsConstant(b)) {
+        var constA = a as ConstantTreeNode;
+        var constB = b as ConstantTreeNode;
+        if (constA.Value > 0.0 || constB.Value > 0.0) {
+          return MakeConstant(1.0);
+        } else {
+          return MakeConstant(-1.0);
+        }
+      } else if (IsConstant(a)) {
+        return MakeOr(b, a);
+      } else if (IsConstant(b)) {
+        var constT = b as ConstantTreeNode;
+        if (constT.Value > 0.0) {
+          // boolean expression is necessarily true
+          return MakeConstant(1.0);
+        } else {
+          // the constant value has no effect on the result of the boolean condition so we can drop the constant term
+          var orNode = orSymbol.CreateTreeNode();
+          orNode.AddSubtree(a);
+          return orNode;
+        }
+      } else {
+        var orNode = orSymbol.CreateTreeNode();
+        orNode.AddSubtree(a);
+        orNode.AddSubtree(b);
+        return orNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeAnd(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      if (IsConstant(a) && IsConstant(b)) {
+        var constA = a as ConstantTreeNode;
+        var constB = b as ConstantTreeNode;
+        if (constA.Value > 0.0 && constB.Value > 0.0) {
+          return MakeConstant(1.0);
+        } else {
+          return MakeConstant(-1.0);
+        }
+      } else if (IsConstant(a)) {
+        return MakeAnd(b, a);
+      } else if (IsConstant(b)) {
+        var constB = b as ConstantTreeNode;
+        if (constB.Value > 0.0) {
+          // the constant value has no effect on the result of the boolean condition so we can drop the constant term
+          var andNode = andSymbol.CreateTreeNode();
+          andNode.AddSubtree(a);
+          return andNode;
+        } else {
+          // boolean expression is necessarily false
+          return MakeConstant(-1.0);
+        }
+      } else {
+        var andNode = andSymbol.CreateTreeNode();
+        andNode.AddSubtree(a);
+        andNode.AddSubtree(b);
+        return andNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeLessThan(ISymbolicExpressionTreeNode leftSide,
+      ISymbolicExpressionTreeNode rightSide) {
+      if (IsConstant(leftSide) && IsConstant(rightSide)) {
+        var lsConst = leftSide as ConstantTreeNode;
+        var rsConst = rightSide as ConstantTreeNode;
+        if (lsConst.Value < rsConst.Value) return MakeConstant(1.0);
+        else return MakeConstant(-1.0);
+      } else {
+        var ltNode = ltSymbol.CreateTreeNode();
+        ltNode.AddSubtree(leftSide);
+        ltNode.AddSubtree(rightSide);
+        return ltNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeGreaterThan(ISymbolicExpressionTreeNode leftSide,
+      ISymbolicExpressionTreeNode rightSide) {
+      if (IsConstant(leftSide) && IsConstant(rightSide)) {
+        var lsConst = leftSide as ConstantTreeNode;
+        var rsConst = rightSide as ConstantTreeNode;
+        if (lsConst.Value > rsConst.Value) return MakeConstant(1.0);
+        else return MakeConstant(-1.0);
+      } else {
+        var gtNode = gtSymbol.CreateTreeNode();
+        gtNode.AddSubtree(leftSide);
+        gtNode.AddSubtree(rightSide);
+        return gtNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeIfThenElse(ISymbolicExpressionTreeNode condition,
+      ISymbolicExpressionTreeNode trueBranch, ISymbolicExpressionTreeNode falseBranch) {
+      if (IsConstant(condition)) {
+        var constT = condition as ConstantTreeNode;
+        if (constT.Value > 0.0) return trueBranch;
+        else return falseBranch;
+      } else {
+        var ifNode = ifThenElseSymbol.CreateTreeNode();
+        if (IsBoolean(condition)) {
+          ifNode.AddSubtree(condition);
+        } else {
+          var gtNode = gtSymbol.CreateTreeNode();
+          gtNode.AddSubtree(condition);
+          gtNode.AddSubtree(MakeConstant(0.0));
+          ifNode.AddSubtree(gtNode);
+        }
+        ifNode.AddSubtree(trueBranch);
+        ifNode.AddSubtree(falseBranch);
+        return ifNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeSine(ISymbolicExpressionTreeNode node) {
+      if (IsConstant(node)) {
+        var constT = node as ConstantTreeNode;
+        return MakeConstant(Math.Sin(constT.Value));
+      } else if (IsFactor(node)) {
+        var factor = node as FactorVariableTreeNode;
+        return MakeFactor(factor.Symbol, factor.VariableName, factor.Weights.Select(Math.Sin));
+      } else if (IsBinFactor(node)) {
+        var binFactor = node as BinaryFactorVariableTreeNode;
+        return MakeBinFactor(binFactor.Symbol, binFactor.VariableName, binFactor.VariableValue, Math.Sin(binFactor.Weight));
+      } else {
+        var sineNode = sineSymbol.CreateTreeNode();
+        sineNode.AddSubtree(node);
+        return sineNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeTangent(ISymbolicExpressionTreeNode node) {
+      if (IsConstant(node)) {
+        var constT = node as ConstantTreeNode;
+        return MakeConstant(Math.Tan(constT.Value));
+      } else if (IsFactor(node)) {
+        var factor = node as FactorVariableTreeNode;
+        return MakeFactor(factor.Symbol, factor.VariableName, factor.Weights.Select(Math.Tan));
+      } else if (IsBinFactor(node)) {
+        var binFactor = node as BinaryFactorVariableTreeNode;
+        return MakeBinFactor(binFactor.Symbol, binFactor.VariableName, binFactor.VariableValue, Math.Tan(binFactor.Weight));
+      } else {
+        var tanNode = tanSymbol.CreateTreeNode();
+        tanNode.AddSubtree(node);
+        return tanNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeCosine(ISymbolicExpressionTreeNode node) {
+      if (IsConstant(node)) {
+        var constT = node as ConstantTreeNode;
+        return MakeConstant(Math.Cos(constT.Value));
+      } else if (IsFactor(node)) {
+        var factor = node as FactorVariableTreeNode;
+        return MakeFactor(factor.Symbol, factor.VariableName, factor.Weights.Select(Math.Cos));
+      } else if (IsBinFactor(node)) {
+        var binFactor = node as BinaryFactorVariableTreeNode;
+        // cos(0) = 1 see similar case for Exp(binfactor)
+        return MakeSum(MakeBinFactor(binFactor.Symbol, binFactor.VariableName, binFactor.VariableValue, Math.Cos(binFactor.Weight) - 1),
+          MakeConstant(1.0));
+      } else {
+        var cosNode = cosineSymbol.CreateTreeNode();
+        cosNode.AddSubtree(node);
+        return cosNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeExp(ISymbolicExpressionTreeNode node) {
+      if (IsConstant(node)) {
+        var constT = node as ConstantTreeNode;
+        return MakeConstant(Math.Exp(constT.Value));
+      } else if (IsFactor(node)) {
+        var factNode = node as FactorVariableTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select(w => Math.Exp(w)));
+      } else if (IsBinFactor(node)) {
+        // exp( binfactor w val=a) = if(val=a) exp(w) else exp(0) = binfactor( (exp(w) - 1) val a) + 1
+        var binFactor = node as BinaryFactorVariableTreeNode;
+        return
+          MakeSum(MakeBinFactor(binFactor.Symbol, binFactor.VariableName, binFactor.VariableValue, Math.Exp(binFactor.Weight) - 1), MakeConstant(1.0));
+      } else if (IsLog(node)) {
+        return node.GetSubtree(0);
+      } else if (IsAddition(node)) {
+        return node.Subtrees.Select(s => MakeExp(s)).Aggregate((s, t) => MakeProduct(s, t));
+      } else if (IsSubtraction(node)) {
+        return node.Subtrees.Select(s => MakeExp(s)).Aggregate((s, t) => MakeProduct(s, Negate(t)));
+      } else {
+        var expNode = expSymbol.CreateTreeNode();
+        expNode.AddSubtree(node);
+        return expNode;
+      }
+    }
+    private static ISymbolicExpressionTreeNode MakeLog(ISymbolicExpressionTreeNode node) {
+      if (IsConstant(node)) {
+        var constT = node as ConstantTreeNode;
+        return MakeConstant(Math.Log(constT.Value));
+      } else if (IsFactor(node)) {
+        var factNode = node as FactorVariableTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select(w => Math.Log(w)));
+      } else if (IsExp(node)) {
+        return node.GetSubtree(0);
+      } else if (IsSquareRoot(node)) {
+        return MakeFraction(MakeLog(node.GetSubtree(0)), MakeConstant(2.0));
+      } else {
+        var logNode = logSymbol.CreateTreeNode();
+        logNode.AddSubtree(node);
+        return logNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeSquare(ISymbolicExpressionTreeNode node) {
+      if (IsConstant(node)) {
+        var constT = node as ConstantTreeNode;
+        return MakeConstant(constT.Value * constT.Value);
+      } else if (IsFactor(node)) {
+        var factNode = node as FactorVariableTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select(w => w * w));
+      } else if (IsBinFactor(node)) {
+        var binFactor = node as BinaryFactorVariableTreeNode;
+        return MakeBinFactor(binFactor.Symbol, binFactor.VariableName, binFactor.VariableValue, binFactor.Weight * binFactor.Weight);
+      } else if (IsSquareRoot(node)) {
+        return node.GetSubtree(0);
+      } else {
+        var sqrNode = sqrSymbol.CreateTreeNode();
+        sqrNode.AddSubtree(node);
+        return sqrNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeSquareRoot(ISymbolicExpressionTreeNode node) {
+      if (IsConstant(node)) {
+        var constT = node as ConstantTreeNode;
+        return MakeConstant(Math.Sqrt(constT.Value));
+      } else if (IsFactor(node)) {
+        var factNode = node as FactorVariableTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select(w => Math.Sqrt(w)));
+      } else if (IsBinFactor(node)) {
+        var binFactor = node as BinaryFactorVariableTreeNode;
+        return MakeBinFactor(binFactor.Symbol, binFactor.VariableName, binFactor.VariableValue, Math.Sqrt(binFactor.Weight));
+      } else if (IsSquare(node)) {
+        return node.GetSubtree(0);
+      } else {
+        var sqrtNode = sqrtSymbol.CreateTreeNode();
+        sqrtNode.AddSubtree(node);
+        return sqrtNode;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeRoot(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      if (IsConstant(a) && IsConstant(b)) {
+        var constA = a as ConstantTreeNode;
+        var constB = b as ConstantTreeNode;
+        return MakeConstant(Math.Pow(constA.Value, 1.0 / Math.Round(constB.Value)));
+      } else if (IsFactor(a) && IsConstant(b)) {
+        var factNode = a as FactorVariableTreeNode;
+        var constNode = b as ConstantTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName,
+          factNode.Weights.Select(w => Math.Pow(w, 1.0 / Math.Round(constNode.Value))));
+      } else if (IsBinFactor(a) && IsConstant(b)) {
+        var binFactor = a as BinaryFactorVariableTreeNode;
+        var constNode = b as ConstantTreeNode;
+        return MakeBinFactor(binFactor.Symbol, binFactor.VariableName, binFactor.VariableValue, Math.Pow(binFactor.Weight, 1.0 / Math.Round(constNode.Value)));
+      } else if (IsConstant(a) && IsFactor(b)) {
+        var constNode = a as ConstantTreeNode;
+        var factNode = b as FactorVariableTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select(w => Math.Pow(constNode.Value, 1.0 / Math.Round(w))));
+      } else if (IsConstant(a) && IsBinFactor(b)) {
+        var constNode = a as ConstantTreeNode;
+        var factNode = b as BinaryFactorVariableTreeNode;
+        return MakeBinFactor(factNode.Symbol, factNode.VariableName, factNode.VariableValue, Math.Pow(constNode.Value, 1.0 / Math.Round(factNode.Weight)));
+      } else if (IsFactor(a) && IsFactor(b) && AreSameTypeAndVariable(a, b)) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as FactorVariableTreeNode;
+        return MakeFactor(node0.Symbol, node0.VariableName, node0.Weights.Zip(node1.Weights, (u, v) => Math.Pow(u, 1.0 / Math.Round(v))));
+      } else if (IsConstant(b)) {
+        var constB = b as ConstantTreeNode;
+        var constBValue = Math.Round(constB.Value);
+        if (constBValue.IsAlmost(1.0)) {
+          return a;
+        } else if (constBValue.IsAlmost(0.0)) {
+          return MakeConstant(1.0);
+        } else if (constBValue.IsAlmost(-1.0)) {
+          return MakeFraction(MakeConstant(1.0), a);
+        } else if (constBValue < 0) {
+          var rootNode = rootSymbol.CreateTreeNode();
+          rootNode.AddSubtree(a);
+          rootNode.AddSubtree(MakeConstant(-1.0 * constBValue));
+          return MakeFraction(MakeConstant(1.0), rootNode);
+        } else {
+          var rootNode = rootSymbol.CreateTreeNode();
+          rootNode.AddSubtree(a);
+          rootNode.AddSubtree(MakeConstant(constBValue));
+          return rootNode;
+        }
+      } else {
+        var rootNode = rootSymbol.CreateTreeNode();
+        rootNode.AddSubtree(a);
+        rootNode.AddSubtree(b);
+        return rootNode;
+      }
+    }
+
+
+    private static ISymbolicExpressionTreeNode MakePower(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      if (IsConstant(a) && IsConstant(b)) {
+        var constA = a as ConstantTreeNode;
+        var constB = b as ConstantTreeNode;
+        return MakeConstant(Math.Pow(constA.Value, Math.Round(constB.Value)));
+      } else if (IsFactor(a) && IsConstant(b)) {
+        var factNode = a as FactorVariableTreeNode;
+        var constNode = b as ConstantTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select(w => Math.Pow(w, Math.Round(constNode.Value))));
+      } else if (IsBinFactor(a) && IsConstant(b)) {
+        var binFactor = a as BinaryFactorVariableTreeNode;
+        var constNode = b as ConstantTreeNode;
+        return MakeBinFactor(binFactor.Symbol, binFactor.VariableName, binFactor.VariableValue, Math.Pow(binFactor.Weight, Math.Round(constNode.Value)));
+      } else if (IsConstant(a) && IsFactor(b)) {
+        var constNode = a as ConstantTreeNode;
+        var factNode = b as FactorVariableTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select(w => Math.Pow(constNode.Value, Math.Round(w))));
+      } else if (IsConstant(a) && IsBinFactor(b)) {
+        var constNode = a as ConstantTreeNode;
+        var factNode = b as BinaryFactorVariableTreeNode;
+        return MakeBinFactor(factNode.Symbol, factNode.VariableName, factNode.VariableValue, Math.Pow(constNode.Value, Math.Round(factNode.Weight)));
+      } else if (IsFactor(a) && IsFactor(b) && AreSameTypeAndVariable(a, b)) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as FactorVariableTreeNode;
+        return MakeFactor(node0.Symbol, node0.VariableName, node0.Weights.Zip(node1.Weights, (u, v) => Math.Pow(u, Math.Round(v))));
+      } else if (IsConstant(b)) {
+        var constB = b as ConstantTreeNode;
+        double exponent = Math.Round(constB.Value);
+        if (exponent.IsAlmost(0.0)) {
+          return MakeConstant(1.0);
+        } else if (exponent.IsAlmost(1.0)) {
+          return a;
+        } else if (exponent.IsAlmost(-1.0)) {
+          return MakeFraction(MakeConstant(1.0), a);
+        } else if (exponent < 0) {
+          var powNode = powSymbol.CreateTreeNode();
+          powNode.AddSubtree(a);
+          powNode.AddSubtree(MakeConstant(-1.0 * exponent));
+          return MakeFraction(MakeConstant(1.0), powNode);
+        } else {
+          var powNode = powSymbol.CreateTreeNode();
+          powNode.AddSubtree(a);
+          powNode.AddSubtree(MakeConstant(exponent));
+          return powNode;
+        }
+      } else {
+        var powNode = powSymbol.CreateTreeNode();
+        powNode.AddSubtree(a);
+        powNode.AddSubtree(b);
+        return powNode;
+      }
+    }
+
+
+    // MakeFraction, MakeProduct and MakeSum take two already simplified trees and create a new simplified tree
+    private static ISymbolicExpressionTreeNode MakeFraction(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      if (IsConstant(a) && IsConstant(b)) {
+        // fold constants
+        return MakeConstant(((ConstantTreeNode)a).Value / ((ConstantTreeNode)b).Value);
+      } else if ((IsConstant(a) && !((ConstantTreeNode)a).Value.IsAlmost(1.0))) {
+        return MakeFraction(MakeConstant(1.0), MakeProduct(b, Invert(a)));
+      } else if (IsVariableBase(a) && IsConstant(b)) {
+        // merge constant values into variable weights
+        var constB = ((ConstantTreeNode)b).Value;
+        ((VariableTreeNodeBase)a).Weight /= constB;
+        return a;
+      } else if (IsFactor(a) && IsConstant(b)) {
+        var factNode = a as FactorVariableTreeNode;
+        var constNode = b as ConstantTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select(w => w / constNode.Value));
+      } else if (IsBinFactor(a) && IsConstant(b)) {
+        var factNode = a as BinaryFactorVariableTreeNode;
+        var constNode = b as ConstantTreeNode;
+        return MakeBinFactor(factNode.Symbol, factNode.VariableName, factNode.VariableValue, factNode.Weight / constNode.Value);
+      } else if (IsFactor(a) && IsFactor(b) && AreSameTypeAndVariable(a, b)) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as FactorVariableTreeNode;
+        return MakeFactor(node0.Symbol, node0.VariableName, node0.Weights.Zip(node1.Weights, (u, v) => u / v));
+      } else if (IsFactor(a) && IsBinFactor(b) && ((IVariableTreeNode)a).VariableName == ((IVariableTreeNode)b).VariableName) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as BinaryFactorVariableTreeNode;
+        var varValues = node0.Symbol.GetVariableValues(node0.VariableName).ToArray();
+        var wi = Array.IndexOf(varValues, node1.VariableValue);
+        if (wi < 0) throw new ArgumentException();
+        var newWeighs = new double[varValues.Length];
+        node0.Weights.CopyTo(newWeighs, 0);
+        for (int i = 0; i < newWeighs.Length; i++)
+          if (wi == i) newWeighs[i] /= node1.Weight;
+          else newWeighs[i] /= 0.0;
+        return MakeFactor(node0.Symbol, node0.VariableName, newWeighs);
+      } else if (IsFactor(a)) {
+        return MakeFraction(MakeConstant(1.0), MakeProduct(b, Invert(a)));
+      } else if (IsVariableBase(a) && IsVariableBase(b) && AreSameTypeAndVariable(a, b) && !IsBinFactor(b)) {
+        // cancel variables (not allowed for bin factors because of division by zero)
+        var aVar = a as VariableTreeNode;
+        var bVar = b as VariableTreeNode;
+        return MakeConstant(aVar.Weight / bVar.Weight);
+      } else if (IsAddition(a) && IsConstant(b)) {
+        return a.Subtrees
+          .Select(x => GetSimplifiedTree(x))
+          .Select(x => MakeFraction(x, GetSimplifiedTree(b)))
+          .Aggregate((c, d) => MakeSum(c, d));
+      } else if (IsMultiplication(a) && IsConstant(b)) {
+        return MakeProduct(a, Invert(b));
+      } else if (IsDivision(a) && IsConstant(b)) {
+        // (a1 / a2) / c => (a1 / (a2 * c))
+        return MakeFraction(a.GetSubtree(0), MakeProduct(a.GetSubtree(1), b));
+      } else if (IsDivision(a) && IsDivision(b)) {
+        // (a1 / a2) / (b1 / b2) => 
+        return MakeFraction(MakeProduct(a.GetSubtree(0), b.GetSubtree(1)), MakeProduct(a.GetSubtree(1), b.GetSubtree(0)));
+      } else if (IsDivision(a)) {
+        // (a1 / a2) / b => (a1 / (a2 * b))
+        return MakeFraction(a.GetSubtree(0), MakeProduct(a.GetSubtree(1), b));
+      } else if (IsDivision(b)) {
+        // a / (b1 / b2) => (a * b2) / b1
+        return MakeFraction(MakeProduct(a, b.GetSubtree(1)), b.GetSubtree(0));
+      } else {
+        var div = divSymbol.CreateTreeNode();
+        div.AddSubtree(a);
+        div.AddSubtree(b);
+        return div;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeSum(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      if (IsConstant(a) && IsConstant(b)) {
+        // fold constants
+        ((ConstantTreeNode)a).Value += ((ConstantTreeNode)b).Value;
+        return a;
+      } else if (IsConstant(a)) {
+        // c + x => x + c
+        // b is not constant => make sure constant is on the right
+        return MakeSum(b, a);
+      } else if (IsConstant(b) && ((ConstantTreeNode)b).Value.IsAlmost(0.0)) {
+        // x + 0 => x
+        return a;
+      } else if (IsFactor(a) && IsConstant(b)) {
+        var factNode = a as FactorVariableTreeNode;
+        var constNode = b as ConstantTreeNode;
+        return MakeFactor(factNode.Symbol, factNode.VariableName, factNode.Weights.Select((w) => w + constNode.Value));
+      } else if (IsFactor(a) && IsFactor(b) && AreSameTypeAndVariable(a, b)) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as FactorVariableTreeNode;
+        return MakeFactor(node0.Symbol, node0.VariableName, node0.Weights.Zip(node1.Weights, (u, v) => u + v));
+      } else if (IsBinFactor(a) && IsFactor(b)) {
+        return MakeSum(b, a);
+      } else if (IsFactor(a) && IsBinFactor(b) &&
+        ((IVariableTreeNode)a).VariableName == ((IVariableTreeNode)b).VariableName) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as BinaryFactorVariableTreeNode;
+        var varValues = node0.Symbol.GetVariableValues(node0.VariableName).ToArray();
+        var wi = Array.IndexOf(varValues, node1.VariableValue);
+        if (wi < 0) throw new ArgumentException();
+        var newWeighs = new double[varValues.Length];
+        node0.Weights.CopyTo(newWeighs, 0);
+        newWeighs[wi] += node1.Weight;
+        return MakeFactor(node0.Symbol, node0.VariableName, newWeighs);
+      } else if (IsAddition(a) && IsAddition(b)) {
+        // merge additions
+        var add = addSymbol.CreateTreeNode();
+        // add all sub trees except for the last
+        for (int i = 0; i < a.Subtrees.Count() - 1; i++) add.AddSubtree(a.GetSubtree(i));
+        for (int i = 0; i < b.Subtrees.Count() - 1; i++) add.AddSubtree(b.GetSubtree(i));
+        if (IsConstant(a.Subtrees.Last()) && IsConstant(b.Subtrees.Last())) {
+          add.AddSubtree(MakeSum(a.Subtrees.Last(), b.Subtrees.Last()));
+        } else if (IsConstant(a.Subtrees.Last())) {
+          add.AddSubtree(b.Subtrees.Last());
+          add.AddSubtree(a.Subtrees.Last());
+        } else {
+          add.AddSubtree(a.Subtrees.Last());
+          add.AddSubtree(b.Subtrees.Last());
+        }
+        MergeVariablesInSum(add);
+        if (add.Subtrees.Count() == 1) {
+          return add.GetSubtree(0);
+        } else {
+          return add;
+        }
+      } else if (IsAddition(b)) {
+        return MakeSum(b, a);
+      } else if (IsAddition(a) && IsConstant(b)) {
+        // a is an addition and b is a constant => append b to a and make sure the constants are merged
+        var add = addSymbol.CreateTreeNode();
+        // add all sub trees except for the last
+        for (int i = 0; i < a.Subtrees.Count() - 1; i++) add.AddSubtree(a.GetSubtree(i));
+        if (IsConstant(a.Subtrees.Last()))
+          add.AddSubtree(MakeSum(a.Subtrees.Last(), b));
+        else {
+          add.AddSubtree(a.Subtrees.Last());
+          add.AddSubtree(b);
+        }
+        return add;
+      } else if (IsAddition(a)) {
+        // a is already an addition => append b
+        var add = addSymbol.CreateTreeNode();
+        add.AddSubtree(b);
+        foreach (var subtree in a.Subtrees) {
+          add.AddSubtree(subtree);
+        }
+        MergeVariablesInSum(add);
+        if (add.Subtrees.Count() == 1) {
+          return add.GetSubtree(0);
+        } else {
+          return add;
+        }
+      } else {
+        var add = addSymbol.CreateTreeNode();
+        add.AddSubtree(a);
+        add.AddSubtree(b);
+        MergeVariablesInSum(add);
+        if (add.Subtrees.Count() == 1) {
+          return add.GetSubtree(0);
+        } else {
+          return add;
+        }
+      }
+    }
+
+    // makes sure variable symbols in sums are combined
+    private static void MergeVariablesInSum(ISymbolicExpressionTreeNode sum) {
+      var subtrees = new List<ISymbolicExpressionTreeNode>(sum.Subtrees);
+      while (sum.Subtrees.Any()) sum.RemoveSubtree(0);
+      var groupedVarNodes = from node in subtrees.OfType<IVariableTreeNode>()
+                            where node.SubtreeCount == 0
+                            group node by GroupId(node) into g
+                            select g;
+      var constant = (from node in subtrees.OfType<ConstantTreeNode>()
+                      select node.Value).DefaultIfEmpty(0.0).Sum();
+      var unchangedSubtrees = subtrees.Where(t => t.SubtreeCount > 0 || !(t is IVariableTreeNode) && !(t is ConstantTreeNode));
+
+      foreach (var variableNodeGroup in groupedVarNodes) {
+        var firstNode = variableNodeGroup.First();
+        if (firstNode is VariableTreeNodeBase) {
+          var representative = firstNode as VariableTreeNodeBase;
+          var weightSum = variableNodeGroup.Cast<VariableTreeNodeBase>().Select(t => t.Weight).Sum();
+          representative.Weight = weightSum;
+          sum.AddSubtree(representative);
+        } else if (firstNode is FactorVariableTreeNode) {
+          var representative = firstNode as FactorVariableTreeNode;
+          foreach (var node in variableNodeGroup.Skip(1).Cast<FactorVariableTreeNode>()) {
+            for (int j = 0; j < representative.Weights.Length; j++) {
+              representative.Weights[j] += node.Weights[j];
+            }
+          }
+          sum.AddSubtree(representative);
+        }
+      }
+      foreach (var unchangedSubtree in unchangedSubtrees)
+        sum.AddSubtree(unchangedSubtree);
+      if (!constant.IsAlmost(0.0)) {
+        sum.AddSubtree(MakeConstant(constant));
+      }
+    }
+
+    // nodes referencing variables can be grouped if they have
+    private static string GroupId(IVariableTreeNode node) {
+      var binaryFactorNode = node as BinaryFactorVariableTreeNode;
+      var factorNode = node as FactorVariableTreeNode;
+      var variableNode = node as VariableTreeNode;
+      var laggedVarNode = node as LaggedVariableTreeNode;
+      if (variableNode != null) {
+        return "var " + variableNode.VariableName;
+      } else if (binaryFactorNode != null) {
+        return "binfactor " + binaryFactorNode.VariableName + " " + binaryFactorNode.VariableValue;
+      } else if (factorNode != null) {
+        return "factor " + factorNode.VariableName;
+      } else if (laggedVarNode != null) {
+        return "lagged " + laggedVarNode.VariableName + " " + laggedVarNode.Lag;
+      } else {
+        throw new NotSupportedException();
+      }
+    }
+
+
+    private static ISymbolicExpressionTreeNode MakeProduct(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      if (IsConstant(a) && IsConstant(b)) {
+        // fold constants
+        return MakeConstant(((ConstantTreeNode)a).Value * ((ConstantTreeNode)b).Value);
+      } else if (IsConstant(a)) {
+        // a * $ => $ * a
+        return MakeProduct(b, a);
+      } else if (IsFactor(a) && IsFactor(b) && AreSameTypeAndVariable(a, b)) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as FactorVariableTreeNode;
+        return MakeFactor(node0.Symbol, node0.VariableName, node0.Weights.Zip(node1.Weights, (u, v) => u * v));
+      } else if (IsBinFactor(a) && IsBinFactor(b) && AreSameTypeAndVariable(a, b)) {
+        var node0 = a as BinaryFactorVariableTreeNode;
+        var node1 = b as BinaryFactorVariableTreeNode;
+        return MakeBinFactor(node0.Symbol, node0.VariableName, node0.VariableValue, node0.Weight * node1.Weight);
+      } else if (IsFactor(a) && IsConstant(b)) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as ConstantTreeNode;
+        return MakeFactor(node0.Symbol, node0.VariableName, node0.Weights.Select(w => w * node1.Value));
+      } else if (IsBinFactor(a) && IsConstant(b)) {
+        var node0 = a as BinaryFactorVariableTreeNode;
+        var node1 = b as ConstantTreeNode;
+        return MakeBinFactor(node0.Symbol, node0.VariableName, node0.VariableValue, node0.Weight * node1.Value);
+      } else if (IsBinFactor(a) && IsFactor(b)) {
+        return MakeProduct(b, a);
+      } else if (IsFactor(a) && IsBinFactor(b) &&
+        ((IVariableTreeNode)a).VariableName == ((IVariableTreeNode)b).VariableName) {
+        var node0 = a as FactorVariableTreeNode;
+        var node1 = b as BinaryFactorVariableTreeNode;
+        var varValues = node0.Symbol.GetVariableValues(node0.VariableName).ToArray();
+        var wi = Array.IndexOf(varValues, node1.VariableValue);
+        if (wi < 0) throw new ArgumentException();
+        return MakeBinFactor(node1.Symbol, node1.VariableName, node1.VariableValue, node1.Weight * node0.Weights[wi]);
+      } else if (IsConstant(b) && ((ConstantTreeNode)b).Value.IsAlmost(1.0)) {
+        // $ * 1.0 => $
+        return a;
+      } else if (IsConstant(b) && ((ConstantTreeNode)b).Value.IsAlmost(0.0)) {
+        return MakeConstant(0);
+      } else if (IsConstant(b) && IsVariableBase(a)) {
+        // multiply constants into variables weights
+        ((VariableTreeNodeBase)a).Weight *= ((ConstantTreeNode)b).Value;
+        return a;
+      } else if (IsConstant(b) && IsAddition(a) ||
+          IsFactor(b) && IsAddition(a) ||
+          IsBinFactor(b) && IsAddition(a)) {
+        // multiply constants into additions
+        return a.Subtrees.Select(x => MakeProduct(GetSimplifiedTree(x), GetSimplifiedTree(b))).Aggregate((c, d) => MakeSum(c, d));
+      } else if (IsDivision(a) && IsDivision(b)) {
+        // (a1 / a2) * (b1 / b2) => (a1 * b1) / (a2 * b2)
+        return MakeFraction(MakeProduct(a.GetSubtree(0), b.GetSubtree(0)), MakeProduct(a.GetSubtree(1), b.GetSubtree(1)));
+      } else if (IsDivision(a)) {
+        // (a1 / a2) * b => (a1 * b) / a2
+        return MakeFraction(MakeProduct(a.GetSubtree(0), b), a.GetSubtree(1));
+      } else if (IsDivision(b)) {
+        // a * (b1 / b2) => (b1 * a) / b2
+        return MakeFraction(MakeProduct(b.GetSubtree(0), a), b.GetSubtree(1));
+      } else if (IsMultiplication(a) && IsMultiplication(b)) {
+        // merge multiplications (make sure constants are merged)
+        var mul = mulSymbol.CreateTreeNode();
+        for (int i = 0; i < a.Subtrees.Count(); i++) mul.AddSubtree(a.GetSubtree(i));
+        for (int i = 0; i < b.Subtrees.Count(); i++) mul.AddSubtree(b.GetSubtree(i));
+        MergeVariablesAndConstantsInProduct(mul);
+        return mul;
+      } else if (IsMultiplication(b)) {
+        return MakeProduct(b, a);
+      } else if (IsMultiplication(a)) {
+        // a is already an multiplication => append b
+        a.AddSubtree(GetSimplifiedTree(b));
+        MergeVariablesAndConstantsInProduct(a);
+        return a;
+      } else {
+        var mul = mulSymbol.CreateTreeNode();
+        mul.AddSubtree(a);
+        mul.AddSubtree(b);
+        MergeVariablesAndConstantsInProduct(mul);
+        return mul;
+      }
+    }
+
+    #endregion
+
+    #region helper functions
+
+    private static bool ContainsVariableCondition(ISymbolicExpressionTreeNode node) {
+      if (node.Symbol is VariableCondition) return true;
+      foreach (var subtree in node.Subtrees)
+        if (ContainsVariableCondition(subtree)) return true;
+      return false;
+    }
+
+    private static ISymbolicExpressionTreeNode AddLagToDynamicNodes(ISymbolicExpressionTreeNode node, int lag) {
+      var laggedTreeNode = node as ILaggedTreeNode;
+      var variableNode = node as VariableTreeNode;
+      var variableConditionNode = node as VariableConditionTreeNode;
+      if (laggedTreeNode != null)
+        laggedTreeNode.Lag += lag;
+      else if (variableNode != null) {
+        var laggedVariableNode = (LaggedVariableTreeNode)laggedVariableSymbol.CreateTreeNode();
+        laggedVariableNode.Lag = lag;
+        laggedVariableNode.VariableName = variableNode.VariableName;
+        return laggedVariableNode;
+      } else if (variableConditionNode != null) {
+        throw new NotSupportedException("Removal of time lags around variable condition symbols is not allowed.");
+      }
+      var subtrees = new List<ISymbolicExpressionTreeNode>(node.Subtrees);
+      while (node.SubtreeCount > 0) node.RemoveSubtree(0);
+      foreach (var subtree in subtrees) {
+        node.AddSubtree(AddLagToDynamicNodes(subtree, lag));
+      }
+      return node;
+    }
+
+    private static bool AreSameTypeAndVariable(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      return GroupId((IVariableTreeNode)a) == GroupId((IVariableTreeNode)b);
+    }
+
+    // helper to combine the constant factors in products and to combine variables (powers of 2, 3...)
+    private static void MergeVariablesAndConstantsInProduct(ISymbolicExpressionTreeNode prod) {
+      var subtrees = new List<ISymbolicExpressionTreeNode>(prod.Subtrees);
+      while (prod.Subtrees.Any()) prod.RemoveSubtree(0);
+      var groupedVarNodes = from node in subtrees.OfType<IVariableTreeNode>()
+                            where node.SubtreeCount == 0
+                            group node by GroupId(node) into g
+                            orderby g.Count()
+                            select g;
+      var constantProduct = (from node in subtrees.OfType<VariableTreeNodeBase>()
+                             select node.Weight)
+        .Concat(from node in subtrees.OfType<ConstantTreeNode>()
+                select node.Value)
+        .DefaultIfEmpty(1.0)
+        .Aggregate((c1, c2) => c1 * c2);
+
+      var unchangedSubtrees = from tree in subtrees
+                              where tree.SubtreeCount > 0 || !(tree is IVariableTreeNode) && !(tree is ConstantTreeNode)
+                              select tree;
+
+      foreach (var variableNodeGroup in groupedVarNodes) {
+        var firstNode = variableNodeGroup.First();
+        if (firstNode is VariableTreeNodeBase) {
+          var representative = (VariableTreeNodeBase)firstNode;
+          representative.Weight = 1.0;
+          if (variableNodeGroup.Count() > 1) {
+            var poly = mulSymbol.CreateTreeNode();
+            for (int p = 0; p < variableNodeGroup.Count(); p++) {
+              poly.AddSubtree((ISymbolicExpressionTreeNode)representative.Clone());
+            }
+            prod.AddSubtree(poly);
+          } else {
+            prod.AddSubtree(representative);
+          }
+        } else if (firstNode is FactorVariableTreeNode) {
+          var representative = (FactorVariableTreeNode)firstNode;
+          foreach (var node in variableNodeGroup.Skip(1).Cast<FactorVariableTreeNode>()) {
+            for (int j = 0; j < representative.Weights.Length; j++) {
+              representative.Weights[j] *= node.Weights[j];
+            }
+          }
+          for (int j = 0; j < representative.Weights.Length; j++) {
+            representative.Weights[j] *= constantProduct;
+          }
+          constantProduct = 1.0;
+          // if the product already contains a factor it is not necessary to multiply a constant below
+          prod.AddSubtree(representative);
+        }
+      }
+
+      foreach (var unchangedSubtree in unchangedSubtrees)
+        prod.AddSubtree(unchangedSubtree);
+
+      if (!constantProduct.IsAlmost(1.0)) {
+        prod.AddSubtree(MakeConstant(constantProduct));
+      }
+    }
+
+
+    /// <summary>
+    /// x => x * -1
+    /// Is only used in cases where it is not necessary to create new tree nodes. Manipulates x directly.
+    /// </summary>
+    /// <param name="x"></param>
+    /// <returns>-x</returns>
+    private static ISymbolicExpressionTreeNode Negate(ISymbolicExpressionTreeNode x) {
+      if (IsConstant(x)) {
+        ((ConstantTreeNode)x).Value *= -1;
+      } else if (IsVariableBase(x)) {
+        var variableTree = (VariableTreeNodeBase)x;
+        variableTree.Weight *= -1.0;
+      } else if (IsFactor(x)) {
+        var factorNode = (FactorVariableTreeNode)x;
+        for (int i = 0; i < factorNode.Weights.Length; i++) factorNode.Weights[i] *= -1;
+      } else if (IsBinFactor(x)) {
+        var factorNode = (BinaryFactorVariableTreeNode)x;
+        factorNode.Weight *= -1;
+      } else if (IsAddition(x)) {
+        // (x0 + x1 + .. + xn) * -1 => (-x0 + -x1 + .. + -xn)        
+        var subtrees = new List<ISymbolicExpressionTreeNode>(x.Subtrees);
+        while (x.Subtrees.Any()) x.RemoveSubtree(0);
+        foreach (var subtree in subtrees) {
+          x.AddSubtree(Negate(subtree));
+        }
+      } else if (IsMultiplication(x) || IsDivision(x)) {
+        // x0 * x1 * .. * xn * -1 => x0 * x1 * .. * -xn
+        var lastSubTree = x.Subtrees.Last();
+        x.RemoveSubtree(x.SubtreeCount - 1);
+        x.AddSubtree(Negate(lastSubTree)); // last is maybe a constant, prefer to negate the constant
+      } else {
+        // any other function
+        return MakeProduct(x, MakeConstant(-1));
+      }
+      return x;
+    }
+
+    /// <summary>
+    /// x => 1/x
+    /// Must create new tree nodes
+    /// </summary>
+    /// <param name="x"></param>
+    /// <returns></returns>
+    private static ISymbolicExpressionTreeNode Invert(ISymbolicExpressionTreeNode x) {
+      if (IsConstant(x)) {
+        return MakeConstant(1.0 / ((ConstantTreeNode)x).Value);
+      } else if (IsFactor(x)) {
+        var factorNode = (FactorVariableTreeNode)x;
+        return MakeFactor(factorNode.Symbol, factorNode.VariableName, factorNode.Weights.Select(w => 1.0 / w));
+      } else if (IsDivision(x)) {
+        return MakeFraction(x.GetSubtree(1), x.GetSubtree(0));
+      } else {
+        // any other function
+        return MakeFraction(MakeConstant(1), x);
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeConstant(double value) {
+      ConstantTreeNode constantTreeNode = (ConstantTreeNode)(constSymbol.CreateTreeNode());
+      constantTreeNode.Value = value;
+      return constantTreeNode;
+    }
+
+    private static ISymbolicExpressionTreeNode MakeFactor(FactorVariable sy, string variableName, IEnumerable<double> weights) {
+      var tree = (FactorVariableTreeNode)sy.CreateTreeNode();
+      tree.VariableName = variableName;
+      tree.Weights = weights.ToArray();
+      return tree;
+    }
+    private static ISymbolicExpressionTreeNode MakeBinFactor(BinaryFactorVariable sy, string variableName, string variableValue, double weight) {
+      var tree = (BinaryFactorVariableTreeNode)sy.CreateTreeNode();
+      tree.VariableName = variableName;
+      tree.VariableValue = variableValue;
+      tree.Weight = weight;
+      return tree;
+    }
+
+
+    #endregion
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/TreeToAutoDiffTermConverter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/TreeToAutoDiffTermConverter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Converters/TreeToAutoDiffTermConverter.cs	(revision 16337)
@@ -0,0 +1,327 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.Serialization;
+using AutoDiff;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public class TreeToAutoDiffTermConverter {
+    public delegate double ParametricFunction(double[] vars, double[] @params);
+
+    public delegate Tuple<double[], double> ParametricFunctionGradient(double[] vars, double[] @params);
+
+    #region helper class
+    public class DataForVariable {
+      public readonly string variableName;
+      public readonly string variableValue; // for factor vars
+      public readonly int lag;
+
+      public DataForVariable(string varName, string varValue, int lag) {
+        this.variableName = varName;
+        this.variableValue = varValue;
+        this.lag = lag;
+      }
+
+      public override bool Equals(object obj) {
+        var other = obj as DataForVariable;
+        if (other == null) return false;
+        return other.variableName.Equals(this.variableName) &&
+               other.variableValue.Equals(this.variableValue) &&
+               other.lag == this.lag;
+      }
+
+      public override int GetHashCode() {
+        return variableName.GetHashCode() ^ variableValue.GetHashCode() ^ lag;
+      }
+    }
+    #endregion
+
+    #region derivations of functions
+    // create function factory for arctangent
+    private static readonly Func<Term, UnaryFunc> arctan = UnaryFunc.Factory(
+      eval: Math.Atan,
+      diff: x => 1 / (1 + x * x));
+
+    private static readonly Func<Term, UnaryFunc> sin = UnaryFunc.Factory(
+      eval: Math.Sin,
+      diff: Math.Cos);
+
+    private static readonly Func<Term, UnaryFunc> cos = UnaryFunc.Factory(
+      eval: Math.Cos,
+      diff: x => -Math.Sin(x));
+
+    private static readonly Func<Term, UnaryFunc> tan = UnaryFunc.Factory(
+      eval: Math.Tan,
+      diff: x => 1 + Math.Tan(x) * Math.Tan(x));
+
+    private static readonly Func<Term, UnaryFunc> erf = UnaryFunc.Factory(
+      eval: alglib.errorfunction,
+      diff: x => 2.0 * Math.Exp(-(x * x)) / Math.Sqrt(Math.PI));
+
+    private static readonly Func<Term, UnaryFunc> norm = UnaryFunc.Factory(
+      eval: alglib.normaldistribution,
+      diff: x => -(Math.Exp(-(x * x)) * Math.Sqrt(Math.Exp(x * x)) * x) / Math.Sqrt(2 * Math.PI));
+
+    #endregion
+
+    public static bool TryConvertToAutoDiff(ISymbolicExpressionTree tree, bool makeVariableWeightsVariable, bool addLinearScalingTerms,
+      out List<DataForVariable> parameters, out double[] initialConstants,
+      out ParametricFunction func,
+      out ParametricFunctionGradient func_grad) {
+
+      // use a transformator object which holds the state (variable list, parameter list, ...) for recursive transformation of the tree
+      var transformator = new TreeToAutoDiffTermConverter(makeVariableWeightsVariable, addLinearScalingTerms);
+      AutoDiff.Term term;
+      try {
+        term = transformator.ConvertToAutoDiff(tree.Root.GetSubtree(0));
+        var parameterEntries = transformator.parameters.ToArray(); // guarantee same order for keys and values
+        var compiledTerm = term.Compile(transformator.variables.ToArray(),
+          parameterEntries.Select(kvp => kvp.Value).ToArray());
+        parameters = new List<DataForVariable>(parameterEntries.Select(kvp => kvp.Key));
+        initialConstants = transformator.initialConstants.ToArray();
+        func = (vars, @params) => compiledTerm.Evaluate(vars, @params);
+        func_grad = (vars, @params) => compiledTerm.Differentiate(vars, @params);
+        return true;
+      } catch (ConversionException) {
+        func = null;
+        func_grad = null;
+        parameters = null;
+        initialConstants = null;
+      }
+      return false;
+    }
+
+    // state for recursive transformation of trees 
+    private readonly
+    List<double> initialConstants;
+    private readonly Dictionary<DataForVariable, AutoDiff.Variable> parameters;
+    private readonly List<AutoDiff.Variable> variables;
+    private readonly bool makeVariableWeightsVariable;
+    private readonly bool addLinearScalingTerms;
+
+    private TreeToAutoDiffTermConverter(bool makeVariableWeightsVariable, bool addLinearScalingTerms) {
+      this.makeVariableWeightsVariable = makeVariableWeightsVariable;
+      this.addLinearScalingTerms = addLinearScalingTerms;
+      this.initialConstants = new List<double>();
+      this.parameters = new Dictionary<DataForVariable, AutoDiff.Variable>();
+      this.variables = new List<AutoDiff.Variable>();
+    }
+
+    private AutoDiff.Term ConvertToAutoDiff(ISymbolicExpressionTreeNode node) {
+      if (node.Symbol is Constant) {
+        initialConstants.Add(((ConstantTreeNode)node).Value);
+        var var = new AutoDiff.Variable();
+        variables.Add(var);
+        return var;
+      }
+      if (node.Symbol is Variable || node.Symbol is BinaryFactorVariable) {
+        var varNode = node as VariableTreeNodeBase;
+        var factorVarNode = node as BinaryFactorVariableTreeNode;
+        // factor variable values are only 0 or 1 and set in x accordingly
+        var varValue = factorVarNode != null ? factorVarNode.VariableValue : string.Empty;
+        var par = FindOrCreateParameter(parameters, varNode.VariableName, varValue);
+
+        if (makeVariableWeightsVariable) {
+          initialConstants.Add(varNode.Weight);
+          var w = new AutoDiff.Variable();
+          variables.Add(w);
+          return AutoDiff.TermBuilder.Product(w, par);
+        } else {
+          return varNode.Weight * par;
+        }
+      }
+      if (node.Symbol is FactorVariable) {
+        var factorVarNode = node as FactorVariableTreeNode;
+        var products = new List<Term>();
+        foreach (var variableValue in factorVarNode.Symbol.GetVariableValues(factorVarNode.VariableName)) {
+          var par = FindOrCreateParameter(parameters, factorVarNode.VariableName, variableValue);
+
+          initialConstants.Add(factorVarNode.GetValue(variableValue));
+          var wVar = new AutoDiff.Variable();
+          variables.Add(wVar);
+
+          products.Add(AutoDiff.TermBuilder.Product(wVar, par));
+        }
+        return AutoDiff.TermBuilder.Sum(products);
+      }
+      if (node.Symbol is LaggedVariable) {
+        var varNode = node as LaggedVariableTreeNode;
+        var par = FindOrCreateParameter(parameters, varNode.VariableName, string.Empty, varNode.Lag);
+
+        if (makeVariableWeightsVariable) {
+          initialConstants.Add(varNode.Weight);
+          var w = new AutoDiff.Variable();
+          variables.Add(w);
+          return AutoDiff.TermBuilder.Product(w, par);
+        } else {
+          return varNode.Weight * par;
+        }
+      }
+      if (node.Symbol is Addition) {
+        List<AutoDiff.Term> terms = new List<Term>();
+        foreach (var subTree in node.Subtrees) {
+          terms.Add(ConvertToAutoDiff(subTree));
+        }
+        return AutoDiff.TermBuilder.Sum(terms);
+      }
+      if (node.Symbol is Subtraction) {
+        List<AutoDiff.Term> terms = new List<Term>();
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          AutoDiff.Term t = ConvertToAutoDiff(node.GetSubtree(i));
+          if (i > 0) t = -t;
+          terms.Add(t);
+        }
+        if (terms.Count == 1) return -terms[0];
+        else return AutoDiff.TermBuilder.Sum(terms);
+      }
+      if (node.Symbol is Multiplication) {
+        List<AutoDiff.Term> terms = new List<Term>();
+        foreach (var subTree in node.Subtrees) {
+          terms.Add(ConvertToAutoDiff(subTree));
+        }
+        if (terms.Count == 1) return terms[0];
+        else return terms.Aggregate((a, b) => new AutoDiff.Product(a, b));
+      }
+      if (node.Symbol is Division) {
+        List<AutoDiff.Term> terms = new List<Term>();
+        foreach (var subTree in node.Subtrees) {
+          terms.Add(ConvertToAutoDiff(subTree));
+        }
+        if (terms.Count == 1) return 1.0 / terms[0];
+        else return terms.Aggregate((a, b) => new AutoDiff.Product(a, 1.0 / b));
+      }
+      if (node.Symbol is Logarithm) {
+        return AutoDiff.TermBuilder.Log(
+          ConvertToAutoDiff(node.GetSubtree(0)));
+      }
+      if (node.Symbol is Exponential) {
+        return AutoDiff.TermBuilder.Exp(
+          ConvertToAutoDiff(node.GetSubtree(0)));
+      }
+      if (node.Symbol is Square) {
+        return AutoDiff.TermBuilder.Power(
+          ConvertToAutoDiff(node.GetSubtree(0)), 2.0);
+      }
+      if (node.Symbol is SquareRoot) {
+        return AutoDiff.TermBuilder.Power(
+          ConvertToAutoDiff(node.GetSubtree(0)), 0.5);
+      }
+      if (node.Symbol is Sine) {
+        return sin(
+          ConvertToAutoDiff(node.GetSubtree(0)));
+      }
+      if (node.Symbol is Cosine) {
+        return cos(
+          ConvertToAutoDiff(node.GetSubtree(0)));
+      }
+      if (node.Symbol is Tangent) {
+        return tan(
+          ConvertToAutoDiff(node.GetSubtree(0)));
+      }
+      if (node.Symbol is Erf) {
+        return erf(
+          ConvertToAutoDiff(node.GetSubtree(0)));
+      }
+      if (node.Symbol is Norm) {
+        return norm(
+          ConvertToAutoDiff(node.GetSubtree(0)));
+      }
+      if (node.Symbol is StartSymbol) {
+        if (addLinearScalingTerms) {
+          // scaling variables α, β are given at the beginning of the parameter vector
+          var alpha = new AutoDiff.Variable();
+          var beta = new AutoDiff.Variable();
+          variables.Add(beta);
+          variables.Add(alpha);
+          var t = ConvertToAutoDiff(node.GetSubtree(0));
+          return t * alpha + beta;
+        } else return ConvertToAutoDiff(node.GetSubtree(0));
+      }
+      throw new ConversionException();
+    }
+
+
+    // for each factor variable value we need a parameter which represents a binary indicator for that variable & value combination
+    // each binary indicator is only necessary once. So we only create a parameter if this combination is not yet available
+    private static Term FindOrCreateParameter(Dictionary<DataForVariable, AutoDiff.Variable> parameters,
+      string varName, string varValue = "", int lag = 0) {
+      var data = new DataForVariable(varName, varValue, lag);
+
+      AutoDiff.Variable par = null;
+      if (!parameters.TryGetValue(data, out par)) {
+        // not found -> create new parameter and entries in names and values lists
+        par = new AutoDiff.Variable();
+        parameters.Add(data, par);
+      }
+      return par;
+    }
+
+    public static bool IsCompatible(ISymbolicExpressionTree tree) {
+      var containsUnknownSymbol = (
+        from n in tree.Root.GetSubtree(0).IterateNodesPrefix()
+        where
+          !(n.Symbol is Variable) &&
+          !(n.Symbol is BinaryFactorVariable) &&
+          !(n.Symbol is FactorVariable) &&
+          !(n.Symbol is LaggedVariable) &&
+          !(n.Symbol is Constant) &&
+          !(n.Symbol is Addition) &&
+          !(n.Symbol is Subtraction) &&
+          !(n.Symbol is Multiplication) &&
+          !(n.Symbol is Division) &&
+          !(n.Symbol is Logarithm) &&
+          !(n.Symbol is Exponential) &&
+          !(n.Symbol is SquareRoot) &&
+          !(n.Symbol is Square) &&
+          !(n.Symbol is Sine) &&
+          !(n.Symbol is Cosine) &&
+          !(n.Symbol is Tangent) &&
+          !(n.Symbol is Erf) &&
+          !(n.Symbol is Norm) &&
+          !(n.Symbol is StartSymbol)
+        select n).Any();
+      return !containsUnknownSymbol;
+    }
+    #region exception class
+    [Serializable]
+    public class ConversionException : Exception {
+
+      public ConversionException() {
+      }
+
+      public ConversionException(string message) : base(message) {
+      }
+
+      public ConversionException(string message, Exception inner) : base(message, inner) {
+      }
+
+      protected ConversionException(
+        SerializationInfo info,
+        StreamingContext context) : base(info, context) {
+      }
+    }
+    #endregion
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/MultiSymbolicDataAnalysisExpressionCreator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/MultiSymbolicDataAnalysisExpressionCreator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/MultiSymbolicDataAnalysisExpressionCreator.cs	(revision 16337)
@@ -0,0 +1,153 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Collections;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Operators;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.PluginInfrastructure;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic.Creators {
+  [StorableClass]
+  public class MultiSymbolicDataAnalysisExpressionCreator : StochasticMultiBranch<ISymbolicDataAnalysisSolutionCreator>,
+    ISymbolicDataAnalysisSolutionCreator,
+    ISymbolicExpressionTreeSizeConstraintOperator,
+  ISymbolicExpressionTreeGrammarBasedOperator {
+    private const string SymbolicExpressionTreeParameterName = "SymbolicExpressionTree";
+    private const string MaximumSymbolicExpressionTreeLengthParameterName = "MaximumSymbolicExpressionTreeLength";
+    private const string MaximumSymbolicExpressionTreeDepthParameterName = "MaximumSymbolicExpressionTreeDepth";
+    private const string SymbolicExpressionTreeGrammarParameterName = "SymbolicExpressionTreeGrammar";
+    private const string ClonedSymbolicExpressionTreeGrammarParameterName = "ClonedSymbolicExpressionTreeGrammar";
+
+    public override bool CanChangeName {
+      get { return false; }
+    }
+    protected override bool CreateChildOperation {
+      get { return true; }
+    }
+
+    #region parameter properties
+    public ILookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter {
+      get { return (ILookupParameter<ISymbolicExpressionTree>)Parameters[SymbolicExpressionTreeParameterName]; }
+    }
+    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeLengthParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeLengthParameterName]; }
+    }
+    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeDepthParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeDepthParameterName]; }
+    }
+    public IValueLookupParameter<ISymbolicExpressionGrammar> SymbolicExpressionTreeGrammarParameter {
+      get { return (IValueLookupParameter<ISymbolicExpressionGrammar>)Parameters[SymbolicExpressionTreeGrammarParameterName]; }
+    }
+    public ILookupParameter<ISymbolicExpressionGrammar> ClonedSymbolicExpressionTreeGrammarParameter {
+      get { return (ILookupParameter<ISymbolicExpressionGrammar>)Parameters[ClonedSymbolicExpressionTreeGrammarParameterName]; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected MultiSymbolicDataAnalysisExpressionCreator(bool deserializing) : base(deserializing) { }
+    protected MultiSymbolicDataAnalysisExpressionCreator(MultiSymbolicDataAnalysisExpressionCreator original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new MultiSymbolicDataAnalysisExpressionCreator(this, cloner); }
+    public MultiSymbolicDataAnalysisExpressionCreator()
+      : base() {
+      Parameters.Add(new LookupParameter<ISymbolicExpressionTree>(SymbolicExpressionTreeParameterName, "The symbolic expression tree on which the operator should be applied."));
+      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeLengthParameterName, "The maximal length (number of nodes) of the symbolic expression tree."));
+      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeDepthParameterName, "The maximal depth of the symbolic expression tree (a tree with one node has depth = 0)."));
+      Parameters.Add(new ValueLookupParameter<ISymbolicExpressionGrammar>(SymbolicExpressionTreeGrammarParameterName, "The tree grammar that defines the correct syntax of symbolic expression trees that should be created."));
+      Parameters.Add(new LookupParameter<ISymbolicExpressionGrammar>(ClonedSymbolicExpressionTreeGrammarParameterName, "An immutable clone of the concrete grammar that is actually used to create and manipulate trees."));
+
+      List<ISymbolicDataAnalysisSolutionCreator> list = new List<ISymbolicDataAnalysisSolutionCreator>();
+      foreach (Type type in ApplicationManager.Manager.GetTypes(typeof(ISymbolicDataAnalysisSolutionCreator))) {
+        if (this.GetType().Assembly != type.Assembly) continue;
+        if (typeof(IMultiOperator<ISymbolicDataAnalysisSolutionCreator>).IsAssignableFrom(type)) continue;
+        list.Add((ISymbolicDataAnalysisSolutionCreator)Activator.CreateInstance(type));
+      }
+      CheckedItemList<ISymbolicDataAnalysisSolutionCreator> checkedItemList = new CheckedItemList<ISymbolicDataAnalysisSolutionCreator>();
+      checkedItemList.AddRange(list.OrderBy(op => op.Name));
+      Operators = checkedItemList.AsReadOnly();
+      Operators_ItemsAdded(this, new CollectionItemsChangedEventArgs<IndexedItem<ISymbolicDataAnalysisSolutionCreator>>(Operators.CheckedItems));
+
+    }
+
+    public override IOperation InstrumentedApply() {
+      if (ClonedSymbolicExpressionTreeGrammarParameter.ActualValue == null) {
+        SymbolicExpressionTreeGrammarParameter.ActualValue.ReadOnly = true;
+        IScope globalScope = ExecutionContext.Scope;
+        while (globalScope.Parent != null)
+          globalScope = globalScope.Parent;
+
+        globalScope.Variables.Add(new Core.Variable(ClonedSymbolicExpressionTreeGrammarParameterName, (ISymbolicExpressionGrammar)SymbolicExpressionTreeGrammarParameter.ActualValue.Clone()));
+      }
+      return base.InstrumentedApply();
+    }
+
+    public ISymbolicExpressionTree CreateTree(IRandom random, ISymbolicExpressionGrammar grammar, int maxTreeLength, int maxTreeDepth) {
+      double sum = Operators.CheckedItems.Sum(o => Probabilities[o.Index]);
+      if (sum.IsAlmost(0)) throw new InvalidOperationException(Name + ": All selected operators have zero probability.");
+      double r = random.NextDouble() * sum;
+      sum = 0;
+      int index = -1;
+      foreach (var indexedItem in Operators.CheckedItems) {
+        sum += Probabilities[indexedItem.Index];
+        if (sum > r) {
+          index = indexedItem.Index;
+          break;
+        }
+      }
+      return Operators[index].CreateTree(random, grammar, maxTreeLength, maxTreeDepth);
+    }
+
+    protected override void Operators_ItemsReplaced(object sender, CollectionItemsChangedEventArgs<IndexedItem<ISymbolicDataAnalysisSolutionCreator>> e) {
+      base.Operators_ItemsReplaced(sender, e);
+      ParameterizeTreeCreators();
+    }
+
+    protected override void Operators_ItemsAdded(object sender, CollectionItemsChangedEventArgs<IndexedItem<ISymbolicDataAnalysisSolutionCreator>> e) {
+      base.Operators_ItemsAdded(sender, e);
+      ParameterizeTreeCreators();
+    }
+    private void ParameterizeTreeCreators() {
+      foreach (IStochasticOperator creator in Operators.OfType<IStochasticOperator>()) {
+        creator.RandomParameter.ActualName = RandomParameter.Name;
+      }
+      foreach (ISymbolicExpressionTreeCreator creator in Operators.OfType<ISymbolicExpressionTreeCreator>()) {
+        creator.SymbolicExpressionTreeParameter.ActualName = SymbolicExpressionTreeParameter.Name;
+      }
+      foreach (ISymbolicExpressionTreeSizeConstraintOperator creator in Operators.OfType<ISymbolicExpressionTreeSizeConstraintOperator>()) {
+        creator.MaximumSymbolicExpressionTreeDepthParameter.ActualName = MaximumSymbolicExpressionTreeDepthParameter.Name;
+        creator.MaximumSymbolicExpressionTreeLengthParameter.ActualName = MaximumSymbolicExpressionTreeLengthParameter.Name;
+      }
+
+      foreach (ISymbolicExpressionTreeGrammarBasedOperator creator in Operators.OfType<ISymbolicExpressionTreeGrammarBasedOperator>()) {
+        creator.SymbolicExpressionTreeGrammarParameter.ActualName = SymbolicExpressionTreeGrammarParameter.Name;
+      }
+    }
+
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionFullTreeCreator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionFullTreeCreator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionFullTreeCreator.cs	(revision 16337)
@@ -0,0 +1,40 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.PluginInfrastructure;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("FullTreeCreator", "An operator that creates new symbolic expression trees using the 'Full' method")]
+  public class SymbolicDataAnalysisExpressionFullTreeCreator : FullTreeCreator, ISymbolicDataAnalysisSolutionCreator {
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionFullTreeCreator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisExpressionFullTreeCreator(SymbolicDataAnalysisExpressionFullTreeCreator original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new SymbolicDataAnalysisExpressionFullTreeCreator(this, cloner); }
+
+    public SymbolicDataAnalysisExpressionFullTreeCreator() : base() { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionGrowTreeCreator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionGrowTreeCreator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionGrowTreeCreator.cs	(revision 16337)
@@ -0,0 +1,40 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.PluginInfrastructure;
+using System;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("GrowTreeCreator", "An operator that creates new symbolic expression trees using the 'Grow' method")]
+  public class SymbolicDataAnalysisExpressionGrowTreeCreator : GrowTreeCreator, ISymbolicDataAnalysisSolutionCreator {
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionGrowTreeCreator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisExpressionGrowTreeCreator(SymbolicDataAnalysisExpressionGrowTreeCreator original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new SymbolicDataAnalysisExpressionGrowTreeCreator(this, cloner); }
+
+    public SymbolicDataAnalysisExpressionGrowTreeCreator() : base() { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator.cs	(revision 16337)
@@ -0,0 +1,40 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.PluginInfrastructure;
+using System;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("RampedHalfAndHalfTreeCreator", "An operator that creates new symbolic expression trees in an alternate way: half the trees are created usign the 'Grow' method while the other half are created using the 'Full' method")]
+  public class SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator : RampedHalfAndHalfTreeCreator, ISymbolicDataAnalysisSolutionCreator {
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator(SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator(this, cloner); }
+
+    public SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator() : base() { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionTreeCreator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionTreeCreator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Creators/SymbolicDataAnalysisExpressionTreeCreator.cs	(revision 16337)
@@ -0,0 +1,38 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("ProbabilisticTreeCreator", "An operator that creates new symbolic expression trees with uniformly distributed length")]
+  public class SymbolicDataAnalysisExpressionTreeCreator : ProbabilisticTreeCreator, ISymbolicDataAnalysisSolutionCreator {
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionTreeCreator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisExpressionTreeCreator(SymbolicDataAnalysisExpressionTreeCreator original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new SymbolicDataAnalysisExpressionTreeCreator(this, cloner); }
+
+    public SymbolicDataAnalysisExpressionTreeCreator() : base() { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/MultiSymbolicDataAnalysisExpressionCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/MultiSymbolicDataAnalysisExpressionCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/MultiSymbolicDataAnalysisExpressionCrossover.cs	(revision 16337)
@@ -0,0 +1,189 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Linq;
+using HeuristicLab.Collections;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Operators;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.PluginInfrastructure;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("MultiSymbolicDataAnalysisExpressionCrossover", "Randomly selects and applies one of its crossovers every time it is called.")]
+  [StorableClass]
+  public class MultiSymbolicDataAnalysisExpressionCrossover<T> : StochasticMultiBranch<ISymbolicExpressionTreeCrossover>,
+    ISymbolicDataAnalysisExpressionCrossover<T> where T : class, IDataAnalysisProblemData {
+    private const string ParentsParameterName = "Parents";
+    private const string SymbolicExpressionTreeParameterName = "SymbolicExpressionTree";
+    private const string MaximumSymbolicExpressionTreeLengthParameterName = "MaximumSymbolicExpressionTreeLength";
+    private const string MaximumSymbolicExpressionTreeDepthParameterName = "MaximumSymbolicExpressionTreeDepth";
+    private const string SymbolicDataAnalysisTreeInterpreterParameterName = "SymbolicExpressionTreeInterpreter";
+    private const string EvaluatorParameterName = "Evaluator";
+    private const string SymbolicDataAnalysisEvaluationPartitionParameterName = "EvaluationPartition";
+    private const string RelativeNumberOfEvaluatedSamplesParameterName = "RelativeNumberOfEvaluatedSamples";
+    private const string ProblemDataParameterName = "ProblemData";
+
+    protected override bool CreateChildOperation {
+      get { return true; }
+    }
+
+    public override bool CanChangeName {
+      get { return false; }
+    }
+
+    #region parameter properties
+    public ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicDataAnalysisTreeInterpreterParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>)Parameters[SymbolicDataAnalysisTreeInterpreterParameterName]; }
+    }
+    public ILookupParameter<ItemArray<ISymbolicExpressionTree>> ParentsParameter {
+      get { return (ScopeTreeLookupParameter<ISymbolicExpressionTree>)Parameters[ParentsParameterName]; }
+    }
+    public ILookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter {
+      get { return (ILookupParameter<ISymbolicExpressionTree>)Parameters[SymbolicExpressionTreeParameterName]; }
+    }
+    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeLengthParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeLengthParameterName]; }
+    }
+    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeDepthParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeDepthParameterName]; }
+    }
+    public ILookupParameter<ISymbolicDataAnalysisSingleObjectiveEvaluator<T>> EvaluatorParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisSingleObjectiveEvaluator<T>>)Parameters[EvaluatorParameterName]; }
+    }
+    public IValueLookupParameter<IntRange> EvaluationPartitionParameter {
+      get { return (IValueLookupParameter<IntRange>)Parameters[SymbolicDataAnalysisEvaluationPartitionParameterName]; }
+    }
+    public IValueLookupParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter {
+      get { return (IValueLookupParameter<PercentValue>)Parameters[RelativeNumberOfEvaluatedSamplesParameterName]; }
+    }
+    public IValueLookupParameter<T> ProblemDataParameter {
+      get { return (IValueLookupParameter<T>)Parameters[ProblemDataParameterName]; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected MultiSymbolicDataAnalysisExpressionCrossover(bool deserializing) : base(deserializing) { }
+    protected MultiSymbolicDataAnalysisExpressionCrossover(MultiSymbolicDataAnalysisExpressionCrossover<T> original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new MultiSymbolicDataAnalysisExpressionCrossover<T>(this, cloner); }
+    public MultiSymbolicDataAnalysisExpressionCrossover()
+      : base() {
+      Parameters.Add(new ValueLookupParameter<PercentValue>(RelativeNumberOfEvaluatedSamplesParameterName, "The relative number of samples of the dataset partition, which should be randomly chosen for evaluation between the start and end index."));
+      Parameters.Add(new ValueLookupParameter<T>(ProblemDataParameterName, "The problem data on which the symbolic data analysis solution should be evaluated."));
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>(SymbolicDataAnalysisTreeInterpreterParameterName, "The interpreter that should be used to calculate the output values of the symbolic data analysis tree."));
+      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeLengthParameterName, "The maximal length (number of nodes) of the symbolic expression tree."));
+      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeDepthParameterName, "The maximal depth of the symbolic expression tree (a tree with one node has depth = 0)."));
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisSingleObjectiveEvaluator<T>>(EvaluatorParameterName, "The single objective solution evaluator"));
+      Parameters.Add(new ValueLookupParameter<IntRange>(SymbolicDataAnalysisEvaluationPartitionParameterName, "The start index of the dataset partition on which the symbolic data analysis solution should be evaluated."));
+      Parameters.Add(new ScopeTreeLookupParameter<ISymbolicExpressionTree>(ParentsParameterName, "The parent symbolic expression trees which should be crossed."));
+      Parameters.Add(new LookupParameter<ISymbolicExpressionTree>(SymbolicExpressionTreeParameterName, "The child symbolic expression tree resulting from the crossover."));
+
+      EvaluatorParameter.Hidden = true;
+      EvaluationPartitionParameter.Hidden = true;
+      SymbolicDataAnalysisTreeInterpreterParameter.Hidden = true;
+      ProblemDataParameter.Hidden = true;
+      RelativeNumberOfEvaluatedSamplesParameter.Hidden = true;
+
+      InitializeOperators();
+      name = "MultiSymbolicDataAnalysisExpressionCrossover";
+
+      SelectedOperatorParameter.ActualName = "SelectedCrossoverOperator";
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      // BackwardsCompatibility3.3
+      #region Backwards compatible code, remove with 3.4
+      if (!Parameters.ContainsKey(SymbolicExpressionTreeParameterName))
+        Parameters.Add(new LookupParameter<ISymbolicExpressionTree>(SymbolicExpressionTreeParameterName, "The symbolic expression tree on which the operator should be applied."));
+      #endregion
+    }
+
+    private void InitializeOperators() {
+      var list = ApplicationManager.Manager.GetInstances<ISymbolicExpressionTreeCrossover>().ToList();
+      var dataAnalysisCrossovers = from type in ApplicationManager.Manager.GetTypes(typeof(ISymbolicDataAnalysisExpressionCrossover<T>))
+                                   where this.GetType().Assembly == type.Assembly
+                                   where !typeof(IMultiOperator<ISymbolicExpressionTreeCrossover>).IsAssignableFrom(type)
+                                   select (ISymbolicDataAnalysisExpressionCrossover<T>)Activator.CreateInstance(type);
+      list.AddRange(dataAnalysisCrossovers);
+
+      var checkedItemList = new CheckedItemList<ISymbolicExpressionTreeCrossover>();
+      checkedItemList.AddRange(list.OrderBy(op => op.Name));
+      Operators = checkedItemList;
+      Operators_ItemsAdded(this, new CollectionItemsChangedEventArgs<IndexedItem<ISymbolicExpressionTreeCrossover>>(Operators.CheckedItems));
+    }
+
+    public ISymbolicExpressionTree Crossover(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1) {
+      double sum = Operators.CheckedItems.Sum(o => Probabilities[o.Index]);
+      if (sum.IsAlmost(0)) throw new InvalidOperationException(Name + ": All selected operators have zero probability.");
+      double r = random.NextDouble() * sum;
+      sum = 0;
+      int index = -1;
+      foreach (var indexedItem in Operators.CheckedItems) {
+        sum += Probabilities[indexedItem.Index];
+        if (sum > r) {
+          index = indexedItem.Index;
+          break;
+        }
+      }
+      return Operators[index].Crossover(random, parent0, parent1);
+    }
+
+    protected override void Operators_ItemsReplaced(object sender, CollectionItemsChangedEventArgs<IndexedItem<ISymbolicExpressionTreeCrossover>> e) {
+      base.Operators_ItemsReplaced(sender, e);
+      ParameterizeCrossovers();
+    }
+
+    protected override void Operators_ItemsAdded(object sender, CollectionItemsChangedEventArgs<IndexedItem<ISymbolicExpressionTreeCrossover>> e) {
+      base.Operators_ItemsAdded(sender, e);
+      ParameterizeCrossovers();
+    }
+
+    private void ParameterizeCrossovers() {
+      foreach (ISymbolicExpressionTreeCrossover op in Operators) {
+        op.SymbolicExpressionTreeParameter.ActualName = SymbolicExpressionTreeParameter.Name;
+        op.ParentsParameter.ActualName = ParentsParameter.Name;
+      }
+      foreach (IStochasticOperator op in Operators.OfType<IStochasticOperator>()) {
+        op.RandomParameter.ActualName = RandomParameter.Name;
+      }
+      foreach (ISymbolicExpressionTreeSizeConstraintOperator op in Operators.OfType<ISymbolicExpressionTreeSizeConstraintOperator>()) {
+        op.MaximumSymbolicExpressionTreeDepthParameter.ActualName = MaximumSymbolicExpressionTreeDepthParameter.Name;
+        op.MaximumSymbolicExpressionTreeLengthParameter.ActualName = MaximumSymbolicExpressionTreeLengthParameter.Name;
+      }
+
+      foreach (ISymbolicDataAnalysisInterpreterOperator op in Operators.OfType<ISymbolicDataAnalysisInterpreterOperator>()) {
+        op.SymbolicDataAnalysisTreeInterpreterParameter.ActualName = SymbolicDataAnalysisTreeInterpreterParameter.Name;
+      }
+      foreach (var op in Operators.OfType<ISymbolicDataAnalysisExpressionCrossover<T>>()) {
+        op.ProblemDataParameter.ActualName = ProblemDataParameter.Name;
+        op.EvaluationPartitionParameter.ActualName = EvaluationPartitionParameter.Name;
+        op.RelativeNumberOfEvaluatedSamplesParameter.ActualName = RelativeNumberOfEvaluatedSamplesParameter.Name;
+        op.EvaluatorParameter.ActualName = EvaluatorParameter.Name;
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionContextAwareCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionContextAwareCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionContextAwareCrossover.cs	(revision 16337)
@@ -0,0 +1,115 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("ContextAwareCrossover", "An operator which deterministically choses the best insertion point for a randomly selected node:\n" +
+                                 "- Take two parent individuals P0 and P1\n" +
+                                 "- Randomly choose a node N from P1\n" +
+                                 "- Test all crossover points from P0 to determine the best location for N to be inserted")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionContextAwareCrossover<T> : SymbolicDataAnalysisExpressionCrossover<T> where T : class, IDataAnalysisProblemData {
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionContextAwareCrossover(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionContextAwareCrossover(SymbolicDataAnalysisExpressionCrossover<T> original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisExpressionContextAwareCrossover()
+      : base() {
+      name = "ContextAwareCrossover";
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionContextAwareCrossover<T>(this, cloner);
+    }
+    public override ISymbolicExpressionTree Crossover(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1) {
+      if (this.ExecutionContext == null)
+        throw new InvalidOperationException("ExecutionContext not set.");
+      List<int> rows = GenerateRowsToEvaluate().ToList();
+      T problemData = ProblemDataParameter.ActualValue;
+      ISymbolicDataAnalysisSingleObjectiveEvaluator<T> evaluator = EvaluatorParameter.ActualValue;
+
+      return Cross(random, parent0, parent1, this.ExecutionContext, evaluator, problemData, rows, MaximumSymbolicExpressionTreeDepth.Value, MaximumSymbolicExpressionTreeLength.Value);
+    }
+
+    /// <summary>
+    /// Takes two parent individuals P0 and P1. 
+    /// Randomly choose a node i from the second parent, then test all possible crossover points from the first parent to determine the best location for i to be inserted.
+    /// </summary>
+    public static ISymbolicExpressionTree Cross(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1, IExecutionContext context,
+                                                ISymbolicDataAnalysisSingleObjectiveEvaluator<T> evaluator, T problemData, List<int> rows, int maxDepth, int maxLength) {
+      // randomly choose a node from the second parent
+      var possibleChildren = new List<ISymbolicExpressionTreeNode>();
+      parent1.Root.ForEachNodePostfix((n) => {
+        if (n.Parent != null && n.Parent != parent1.Root)
+          possibleChildren.Add(n);
+      });
+
+      var selectedChild = possibleChildren.SampleRandom(random);
+      var crossoverPoints = new List<CutPoint>();
+      var qualities = new List<Tuple<CutPoint, double>>();
+
+      parent0.Root.ForEachNodePostfix((n) => {
+        if (n.Parent != null && n.Parent != parent0.Root) {
+          var totalDepth = parent0.Root.GetBranchLevel(n) + selectedChild.GetDepth();
+          var totalLength = parent0.Root.GetLength() - n.GetLength() + selectedChild.GetLength();
+          if (totalDepth <= maxDepth && totalLength <= maxLength) {
+            var crossoverPoint = new CutPoint(n.Parent, n);
+            if (crossoverPoint.IsMatchingPointType(selectedChild))
+              crossoverPoints.Add(crossoverPoint);
+          }
+        }
+      });
+
+      if (crossoverPoints.Any()) {
+        // this loop will perform two swap operations per each crossover point
+        foreach (var crossoverPoint in crossoverPoints) {
+          // save the old parent so we can restore it later
+          var parent = selectedChild.Parent;
+          // perform a swap and check the quality of the solution
+          Swap(crossoverPoint, selectedChild);
+          IExecutionContext childContext = new ExecutionContext(context, evaluator, context.Scope);
+          double quality = evaluator.Evaluate(childContext, parent0, problemData, rows);
+          qualities.Add(new Tuple<CutPoint, double>(crossoverPoint, quality));
+          // restore the correct parent
+          selectedChild.Parent = parent;
+          // swap the replaced subtree back into the tree so that the structure is preserved
+          Swap(crossoverPoint, crossoverPoint.Child);
+        }
+
+        qualities.Sort((a, b) => a.Item2.CompareTo(b.Item2)); // assuming this sorts the list in ascending order
+        var crossoverPoint0 = evaluator.Maximization ? qualities.Last().Item1 : qualities.First().Item1;
+        // swap the node that would create the best offspring
+        // this last swap makes a total of (2 * crossoverPoints.Count() + 1) swap operations.
+        Swap(crossoverPoint0, selectedChild);
+      }
+
+      return parent0;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionCrossover.cs	(revision 16337)
@@ -0,0 +1,161 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisExpressionCrossover<T> : SymbolicExpressionTreeCrossover, ISymbolicDataAnalysisExpressionCrossover<T> where T : class, IDataAnalysisProblemData {
+    private const string SymbolicDataAnalysisTreeInterpreterParameterName = "SymbolicExpressionTreeInterpreter";
+    private const string ProblemDataParameterName = "ProblemData";
+    private const string EvaluatorParameterName = "Evaluator";
+    private const string EvaluationPartitionParameterName = "EvaluationPartition";
+    private const string RelativeNumberOfEvaluatedSamplesParameterName = "RelativeNumberOfEvaluatedSamples";
+    private const string MaximumSymbolicExpressionTreeLengthParameterName = "MaximumSymbolicExpressionTreeLength";
+    private const string MaximumSymbolicExpressionTreeDepthParameterName = "MaximumSymbolicExpressionTreeDepth";
+
+    #region Parameter properties
+    public ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicDataAnalysisTreeInterpreterParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>)Parameters[SymbolicDataAnalysisTreeInterpreterParameterName]; }
+    }
+    public IValueLookupParameter<T> ProblemDataParameter {
+      get { return (IValueLookupParameter<T>)Parameters[ProblemDataParameterName]; }
+    }
+    public ILookupParameter<ISymbolicDataAnalysisSingleObjectiveEvaluator<T>> EvaluatorParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisSingleObjectiveEvaluator<T>>)Parameters[EvaluatorParameterName]; }
+    }
+    public IValueLookupParameter<IntRange> EvaluationPartitionParameter {
+      get { return (IValueLookupParameter<IntRange>)Parameters[EvaluationPartitionParameterName]; }
+    }
+    public IValueLookupParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter {
+      get { return (IValueLookupParameter<PercentValue>)Parameters[RelativeNumberOfEvaluatedSamplesParameterName]; }
+    }
+    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeLengthParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeLengthParameterName]; }
+    }
+    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeDepthParameter {
+      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeDepthParameterName]; }
+    }
+    #endregion
+
+    #region Properties
+    public IntValue MaximumSymbolicExpressionTreeLength {
+      get { return MaximumSymbolicExpressionTreeLengthParameter.ActualValue; }
+    }
+    public IntValue MaximumSymbolicExpressionTreeDepth {
+      get { return MaximumSymbolicExpressionTreeDepthParameter.ActualValue; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionCrossover(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisExpressionCrossover(SymbolicDataAnalysisExpressionCrossover<T> original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisExpressionCrossover()
+      : base() {
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>(SymbolicDataAnalysisTreeInterpreterParameterName, "The interpreter that should be used to calculate the output values of the symbolic data analysis tree."));
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisSingleObjectiveEvaluator<T>>(EvaluatorParameterName, "The single objective solution evaluator"));
+      Parameters.Add(new ValueLookupParameter<T>(ProblemDataParameterName, "The problem data on which the symbolic data analysis solution should be evaluated."));
+      Parameters.Add(new ValueLookupParameter<IntRange>(EvaluationPartitionParameterName, "The start index of the dataset partition on which the symbolic data analysis solution should be evaluated."));
+      Parameters.Add(new ValueLookupParameter<PercentValue>(RelativeNumberOfEvaluatedSamplesParameterName, "The relative number of samples of the dataset partition, which should be randomly chosen for evaluation between the start and end index."));
+      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeDepthParameterName, "The maximum tree depth."));
+      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeLengthParameterName, "The maximum tree length."));
+
+      EvaluatorParameter.Hidden = true;
+      EvaluationPartitionParameter.Hidden = true;
+      SymbolicDataAnalysisTreeInterpreterParameter.Hidden = true;
+      ProblemDataParameter.Hidden = true;
+      RelativeNumberOfEvaluatedSamplesParameter.Hidden = true;
+    }
+
+    /// <summary>
+    /// Creates a SymbolicExpressionTreeNode reusing the root and start symbols (since they are expensive to create).
+    /// </summary>
+    /// <param name="random"></param>
+    /// <param name="node"></param>
+    /// <param name="rootSymbol"></param>
+    /// <param name="startSymbol"></param>
+    /// <returns></returns>
+    protected static ISymbolicExpressionTree CreateTreeFromNode(IRandom random, ISymbolicExpressionTreeNode node, ISymbol rootSymbol, ISymbol startSymbol) {
+      var rootNode = new SymbolicExpressionTreeTopLevelNode(rootSymbol);
+      if (rootNode.HasLocalParameters) rootNode.ResetLocalParameters(random);
+
+      var startNode = new SymbolicExpressionTreeTopLevelNode(startSymbol);
+      if (startNode.HasLocalParameters) startNode.ResetLocalParameters(random);
+
+      startNode.AddSubtree(node);
+      rootNode.AddSubtree(startNode);
+
+      return new SymbolicExpressionTree(rootNode);
+    }
+
+    protected IEnumerable<int> GenerateRowsToEvaluate() {
+      return GenerateRowsToEvaluate(RelativeNumberOfEvaluatedSamplesParameter.ActualValue.Value);
+    }
+
+    protected IEnumerable<int> GenerateRowsToEvaluate(double percentageOfRows) {
+      IEnumerable<int> rows;
+      int samplesStart = EvaluationPartitionParameter.ActualValue.Start;
+      int samplesEnd = EvaluationPartitionParameter.ActualValue.End;
+      int testPartitionStart = ProblemDataParameter.ActualValue.TestPartition.Start;
+      int testPartitionEnd = ProblemDataParameter.ActualValue.TestPartition.End;
+
+      if (samplesEnd < samplesStart) throw new ArgumentException("Start value is larger than end value.");
+
+      if (percentageOfRows.IsAlmost(1.0))
+        rows = Enumerable.Range(samplesStart, samplesEnd - samplesStart);
+      else {
+        int seed = RandomParameter.ActualValue.Next();
+        int count = (int)((samplesEnd - samplesStart) * percentageOfRows);
+        if (count == 0) count = 1;
+        rows = RandomEnumerable.SampleRandomNumbers(seed, samplesStart, samplesEnd, count);
+      }
+
+      return rows.Where(i => i < testPartitionStart || testPartitionEnd <= i);
+    }
+
+    protected static void Swap(CutPoint crossoverPoint, ISymbolicExpressionTreeNode selectedBranch) {
+      if (crossoverPoint.Child != null) {
+        // manipulate the tree of parent0 in place
+        // replace the branch in tree0 with the selected branch from tree1
+        crossoverPoint.Parent.RemoveSubtree(crossoverPoint.ChildIndex);
+        if (selectedBranch != null) {
+          crossoverPoint.Parent.InsertSubtree(crossoverPoint.ChildIndex, selectedBranch);
+        }
+      } else {
+        // child is null (additional child should be added under the parent)
+        if (selectedBranch != null) {
+          crossoverPoint.Parent.AddSubtree(selectedBranch);
+        }
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDepthConstrainedCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDepthConstrainedCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDepthConstrainedCrossover.cs	(revision 16337)
@@ -0,0 +1,144 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("DepthConstrainedCrossover", "An operator which performs subtree swapping within a specific depth range. The range parameter controls the crossover behavior:\n" +
+                                     "- HighLevel (upper 25% of the tree)\n" +
+                                     "- Standard (mid 50% of the tree)\n" +
+                                     "- LowLevel (lower 25% of the tree)")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionDepthConstrainedCrossover<T> :
+    SymbolicDataAnalysisExpressionCrossover<T> where T : class, IDataAnalysisProblemData {
+    private enum Ranges { HighLevel, Standard, LowLevel };
+    private const string DepthRangeParameterName = "DepthRange";
+
+    #region Parameter properties
+    public IConstrainedValueParameter<StringValue> DepthRangeParameter {
+      get { return (IConstrainedValueParameter<StringValue>)Parameters[DepthRangeParameterName]; }
+    }
+    #endregion
+
+    #region Properties
+    public StringValue DepthRange {
+      get { return (StringValue)DepthRangeParameter.ActualValue; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionDepthConstrainedCrossover(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionDepthConstrainedCrossover(SymbolicDataAnalysisExpressionCrossover<T> original, Cloner cloner)
+      : base(original, cloner) { }
+    public SymbolicDataAnalysisExpressionDepthConstrainedCrossover()
+      : base() {
+      Parameters.Add(new ConstrainedValueParameter<StringValue>(DepthRangeParameterName, "Depth range specifier"));
+      DepthRangeParameter.ValidValues.Add(new StringValue(Enum.GetName(typeof(Ranges), Ranges.HighLevel)).AsReadOnly());
+      DepthRangeParameter.ValidValues.Add(new StringValue(Enum.GetName(typeof(Ranges), Ranges.Standard)).AsReadOnly());
+      DepthRangeParameter.ValidValues.Add(new StringValue(Enum.GetName(typeof(Ranges), Ranges.LowLevel)).AsReadOnly());
+      name = "DepthConstrainedCrossover";
+    }
+    public override IDeepCloneable Clone(Cloner cloner) { return new SymbolicDataAnalysisExpressionDepthConstrainedCrossover<T>(this, cloner); }
+
+    public override ISymbolicExpressionTree Crossover(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1) {
+      return Cross(random, parent0, parent1, MaximumSymbolicExpressionTreeDepth.Value, MaximumSymbolicExpressionTreeLength.Value, DepthRange.Value);
+    }
+
+
+    /// <summary>
+    /// Takes two parent individuals P0 and P1. 
+    /// Randomly choose nodes that fall within the specified depth range in both parents.
+    /// </summary>
+    /// <param name="random">Pseudo-random number generator.</param>
+    /// <param name="parent0">First parent.</param>
+    /// <param name="parent1">Second parent.</param>
+    /// <param name="maxDepth">Maximum allowed length depth.</param>
+    /// <param name="maxLength">Maximum allowed tree length.</param>
+    /// <param name="mode">Controls the crossover behavior: 
+    /// - HighLevel (upper 25% of the tree),
+    /// - Standard (mid 50%)
+    /// - LowLevel (low 25%)</param>
+    /// <returns></returns>
+    public static ISymbolicExpressionTree Cross(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1, int maxDepth, int maxLength, string mode) {
+      int depth = parent0.Root.GetDepth() - 1; // substract 1 because the tree levels are counted from 0 
+      var depthRange = new IntRange();
+      const int depthOffset = 2; // skip the first 2 levels (root + startNode)
+      switch ((Ranges)Enum.Parse(typeof(Ranges), mode)) {
+        case Ranges.HighLevel:
+          depthRange.Start = depthOffset; // skip the first 2 levels (root + startNode)
+          depthRange.End = depthRange.Start + (int)Math.Round(depth * 0.25);
+          break;
+        case Ranges.Standard:
+          depthRange.Start = depthOffset + (int)Math.Round(depth * 0.25);
+          depthRange.End = depthRange.Start + (int)Math.Round(depth * 0.5);
+          break;
+        case Ranges.LowLevel:
+          depthRange.Start = depthOffset + (int)Math.Round(depth * 0.75);
+          depthRange.End = Math.Max(depthRange.Start, depth);
+          break;
+      }
+
+      // make sure that the depth range does not exceeded the actual depth of parent0
+      if (depthRange.Start > depth)
+        depthRange.Start = depth;
+      if (depthRange.End < depthRange.Start)
+        depthRange.End = depthRange.Start;
+
+      var crossoverPoints0 = (from node in GetNodesAtDepth(parent0, depthRange) select new CutPoint(node.Parent, node)).ToList();
+
+      if (crossoverPoints0.Count == 0)
+        throw new Exception("No crossover points available in the first parent");
+
+      var crossoverPoint0 = crossoverPoints0.SampleRandom(random);
+      int level = parent0.Root.GetBranchLevel(crossoverPoint0.Child);
+      int length = parent0.Root.GetLength() - crossoverPoint0.Child.GetLength();
+
+      var allowedBranches = (from s in GetNodesAtDepth(parent1, depthRange)
+                             where s.GetDepth() + level <= maxDepth
+                             where s.GetLength() + length <= maxLength
+                             where crossoverPoint0.IsMatchingPointType(s)
+                             select s).ToList();
+      if (allowedBranches.Count == 0) return parent0;
+
+      var selectedBranch = allowedBranches.SampleRandom(random);
+      Swap(crossoverPoint0, selectedBranch);
+      return parent0;
+    }
+
+    private static IEnumerable<ISymbolicExpressionTreeNode> GetNodesAtDepth(ISymbolicExpressionTree tree, IntRange depthRange) {
+      var treeDepth = tree.Root.GetDepth();
+      return from node in tree.Root.IterateNodesPostfix()
+             let depth = treeDepth - node.GetDepth()
+             where depthRange.Start <= depth
+             where depth <= depthRange.End
+             select node;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDeterministicBestCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDeterministicBestCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDeterministicBestCrossover.cs	(revision 16337)
@@ -0,0 +1,110 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("DeterministicBestCrossover", "An operator which performs subtree swapping by choosing the best subtree to be swapped in a certain position:\n" +
+                                      "- Take two parent individuals P0 and P1\n" +
+                                      "- Randomly choose a crossover point C from P0\n" +
+                                      "- Test all nodes from P1 to determine the one that produces the best child when inserted at place C in P0")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionDeterministicBestCrossover<T> : SymbolicDataAnalysisExpressionCrossover<T> where T : class, IDataAnalysisProblemData {
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionDeterministicBestCrossover(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionDeterministicBestCrossover(SymbolicDataAnalysisExpressionCrossover<T> original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisExpressionDeterministicBestCrossover()
+      : base() {
+      name = "DeterministicBestCrossover";
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionDeterministicBestCrossover<T>(this, cloner);
+    }
+    public override ISymbolicExpressionTree Crossover(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1) {
+      if (this.ExecutionContext == null)
+        throw new InvalidOperationException("ExecutionContext not set.");
+      List<int> rows = GenerateRowsToEvaluate().ToList();
+      T problemData = ProblemDataParameter.ActualValue;
+      ISymbolicDataAnalysisSingleObjectiveEvaluator<T> evaluator = EvaluatorParameter.ActualValue;
+
+      return Cross(random, parent0, parent1, this.ExecutionContext, evaluator, problemData, rows, MaximumSymbolicExpressionTreeDepth.Value, MaximumSymbolicExpressionTreeLength.Value);
+    }
+
+    /// <summary>
+    /// Takes two parent individuals P0 and P1. 
+    /// Randomly choose a node i from the first parent, then test all nodes j from the second parent to determine the best child that would be obtained by swapping i for j.
+    /// </summary>
+    public static ISymbolicExpressionTree Cross(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1, IExecutionContext context,
+                                                ISymbolicDataAnalysisSingleObjectiveEvaluator<T> evaluator, T problemData, List<int> rows, int maxDepth, int maxLength) {
+      var crossoverPoints0 = new List<CutPoint>();
+      parent0.Root.ForEachNodePostfix((n) => {
+        if (n.Parent != null && n.Parent != parent0.Root)
+          crossoverPoints0.Add(new CutPoint(n.Parent, n));
+      });
+
+      CutPoint crossoverPoint0 = crossoverPoints0.SampleRandom(random);
+      int level = parent0.Root.GetBranchLevel(crossoverPoint0.Child);
+      int length = parent0.Root.GetLength() - crossoverPoint0.Child.GetLength();
+
+      var allowedBranches = new List<ISymbolicExpressionTreeNode>();
+      parent1.Root.ForEachNodePostfix((n) => {
+        if (n.Parent != null && n.Parent != parent1.Root) {
+          if (n.GetDepth() + level <= maxDepth && n.GetLength() + length <= maxLength && crossoverPoint0.IsMatchingPointType(n))
+            allowedBranches.Add(n);
+        }
+      });
+
+      if (allowedBranches.Count == 0)
+        return parent0;
+
+      // create symbols in order to improvize an ad-hoc tree so that the child can be evaluated
+      ISymbolicExpressionTreeNode selectedBranch = null;
+      var nodeQualities = new List<Tuple<ISymbolicExpressionTreeNode, double>>();
+      var originalChild = crossoverPoint0.Child;
+
+      foreach (var node in allowedBranches) {
+        var parent = node.Parent;
+        Swap(crossoverPoint0, node); // the swap will set the nodes parent to crossoverPoint0.Parent
+        IExecutionContext childContext = new ExecutionContext(context, evaluator, context.Scope);
+        double quality = evaluator.Evaluate(childContext, parent0, problemData, rows);
+        Swap(crossoverPoint0, originalChild); // swap the child back (so that the next swap will not affect the currently swapped node from parent1)
+        nodeQualities.Add(new Tuple<ISymbolicExpressionTreeNode, double>(node, quality));
+        node.Parent = parent; // restore correct parent
+      }
+
+      nodeQualities.Sort((a, b) => a.Item2.CompareTo(b.Item2));
+      selectedBranch = evaluator.Maximization ? nodeQualities.Last().Item1 : nodeQualities.First().Item1;
+
+      // swap the node that would create the best offspring
+      Swap(crossoverPoint0, selectedBranch);
+      return parent0;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDiversityPreservingCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDiversityPreservingCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionDiversityPreservingCrossover.cs	(revision 16337)
@@ -0,0 +1,146 @@
+﻿using System;
+using System.Collections.Generic;
+using System.Linq;
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+using static HeuristicLab.Problems.DataAnalysis.Symbolic.SymbolicExpressionHashExtensions;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("DiversityCrossover", "Simple crossover operator prioritizing internal nodes according to the given probability.")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionDiversityPreservingCrossover<T> : SymbolicDataAnalysisExpressionCrossover<T> where T : class, IDataAnalysisProblemData {
+
+    private const string InternalCrossoverPointProbabilityParameterName = "InternalCrossoverPointProbability";
+    private const string WindowingParameterName = "Windowing";
+    private const string ProportionalSamplingParameterName = "ProportionalSampling";
+
+    private static readonly Func<byte[], ulong> hashFunction = HashUtil.JSHash;
+
+    #region Parameter Properties
+    public IValueLookupParameter<PercentValue> InternalCrossoverPointProbabilityParameter {
+      get { return (IValueLookupParameter<PercentValue>)Parameters[InternalCrossoverPointProbabilityParameterName]; }
+    }
+
+    public IValueLookupParameter<BoolValue> WindowingParameter {
+      get { return (IValueLookupParameter<BoolValue>)Parameters[WindowingParameterName]; }
+    }
+
+    public IValueLookupParameter<BoolValue> ProportionalSamplingParameter {
+      get { return (IValueLookupParameter<BoolValue>)Parameters[ProportionalSamplingParameterName]; }
+    }
+    #endregion
+
+    #region Properties
+    public PercentValue InternalCrossoverPointProbability {
+      get { return InternalCrossoverPointProbabilityParameter.ActualValue; }
+    }
+
+    public BoolValue Windowing {
+      get { return WindowingParameter.ActualValue; }
+    }
+
+    public BoolValue ProportionalSampling {
+      get { return ProportionalSamplingParameter.ActualValue; }
+    }
+    #endregion
+
+    public SymbolicDataAnalysisExpressionDiversityPreservingCrossover() {
+      name = "DiversityCrossover";
+      Parameters.Add(new ValueLookupParameter<PercentValue>(InternalCrossoverPointProbabilityParameterName, "The probability to select an internal crossover point (instead of a leaf node).", new PercentValue(0.9)));
+      Parameters.Add(new ValueLookupParameter<BoolValue>(WindowingParameterName, "Use proportional sampling with windowing for cutpoint selection.", new BoolValue(false)));
+      Parameters.Add(new ValueLookupParameter<BoolValue>(ProportionalSamplingParameterName, "Select cutpoints proportionally using probabilities as weights instead of randomly.", new BoolValue(true)));
+    }
+
+    private SymbolicDataAnalysisExpressionDiversityPreservingCrossover(SymbolicDataAnalysisExpressionDiversityPreservingCrossover<T> original, Cloner cloner) : base(original, cloner) {
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionDiversityPreservingCrossover<T>(this, cloner);
+    }
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionDiversityPreservingCrossover(bool deserializing) : base(deserializing) { }
+
+    private static ISymbolicExpressionTreeNode ActualRoot(ISymbolicExpressionTree tree) {
+      return tree.Root.GetSubtree(0).GetSubtree(0);
+    }
+
+    public static ISymbolicExpressionTree Cross(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1, double internalCrossoverPointProbability, int maxLength, int maxDepth, bool windowing, bool proportionalSampling = false) {
+      var leafCrossoverPointProbability = 1 - internalCrossoverPointProbability;
+
+      var nodes0 = ActualRoot(parent0).MakeNodes().Sort(hashFunction);
+      var nodes1 = ActualRoot(parent1).MakeNodes().Sort(hashFunction);
+
+      IList<HashNode<ISymbolicExpressionTreeNode>> sampled0;
+      IList<HashNode<ISymbolicExpressionTreeNode>> sampled1;
+
+      if (proportionalSampling) {
+        var p = internalCrossoverPointProbability;
+        var weights0 = nodes0.Select(x => x.IsLeaf ? 1 - p : p);
+        sampled0 = nodes0.SampleProportionalWithoutRepetition(random, nodes0.Length, weights0, windowing: windowing).ToArray();
+
+        var weights1 = nodes1.Select(x => x.IsLeaf ? 1 - p : p);
+        sampled1 = nodes1.SampleProportionalWithoutRepetition(random, nodes1.Length, weights1, windowing: windowing).ToArray();
+      } else {
+        sampled0 = ChooseNodes(random, nodes0, internalCrossoverPointProbability).ShuffleInPlace(random);
+        sampled1 = ChooseNodes(random, nodes1, internalCrossoverPointProbability).ShuffleInPlace(random);
+      }
+
+      foreach (var selected in sampled0) {
+        var cutpoint = new CutPoint(selected.Data.Parent, selected.Data);
+
+        var maxAllowedDepth = maxDepth - parent0.Root.GetBranchLevel(selected.Data);
+        var maxAllowedLength = maxLength - (parent0.Length - selected.Data.GetLength());
+
+        foreach (var candidate in sampled1) {
+          if (candidate.CalculatedHashValue == selected.CalculatedHashValue
+            || candidate.Data.GetDepth() > maxAllowedDepth
+            || candidate.Data.GetLength() > maxAllowedLength
+            || !cutpoint.IsMatchingPointType(candidate.Data)) {
+            continue;
+          }
+
+          Swap(cutpoint, candidate.Data);
+          return parent0;
+        }
+      }
+      return parent0;
+    }
+
+    public override ISymbolicExpressionTree Crossover(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1) {
+      if (this.ExecutionContext == null) {
+        throw new InvalidOperationException("ExecutionContext not set.");
+      }
+
+      var maxDepth = MaximumSymbolicExpressionTreeDepth.Value;
+      var maxLength = MaximumSymbolicExpressionTreeLength.Value;
+
+      var internalCrossoverPointProbability = InternalCrossoverPointProbability.Value;
+      var windowing = Windowing.Value;
+      var proportionalSampling = ProportionalSampling.Value;
+
+      return Cross(random, parent0, parent1, internalCrossoverPointProbability, maxLength, maxDepth, windowing, proportionalSampling);
+    }
+
+    private static List<HashNode<ISymbolicExpressionTreeNode>> ChooseNodes(IRandom random, IEnumerable<HashNode<ISymbolicExpressionTreeNode>> nodes, double internalCrossoverPointProbability) {
+      var list = new List<HashNode<ISymbolicExpressionTreeNode>>();
+
+      var chooseInternal = random.NextDouble() < internalCrossoverPointProbability;
+
+      if (chooseInternal) {
+        list.AddRange(nodes.Where(x => !x.IsLeaf && x.Data.Parent != null));
+      }
+      if (!chooseInternal || list.Count == 0) {
+        list.AddRange(nodes.Where(x => x.IsLeaf && x.Data.Parent != null));
+      }
+
+      return list;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover.cs	(revision 16337)
@@ -0,0 +1,150 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("ProbabilisticFunctionalCrossover", "An operator which performs subtree swapping based on the behavioral similarity between subtrees:\n" +
+                                            "- Take two parent individuals P0 and P1\n" +
+                                            "- Randomly choose a node N from P0\n" +
+                                            "- For each matching node M from P1, calculate the behavioral distance:\n" +
+                                            "\t\tD(N,M) = 0.5 * ( abs(max(N) - max(M)) + abs(min(N) - min(M)) )\n" +
+                                            "- Make a probabilistic weighted choice of node M from P1, based on the inversed and normalized behavioral distance")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover<T> : SymbolicDataAnalysisExpressionCrossover<T> where T : class, IDataAnalysisProblemData {
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover(SymbolicDataAnalysisExpressionCrossover<T> original, Cloner cloner)
+      : base(original, cloner) { }
+    public SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover()
+      : base() {
+      name = "ProbabilisticFunctionalCrossover";
+    }
+    public override IDeepCloneable Clone(Cloner cloner) { return new SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover<T>(this, cloner); }
+
+    public override ISymbolicExpressionTree Crossover(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1) {
+      ISymbolicDataAnalysisExpressionTreeInterpreter interpreter = SymbolicDataAnalysisTreeInterpreterParameter.ActualValue;
+      List<int> rows = GenerateRowsToEvaluate().ToList();
+      T problemData = ProblemDataParameter.ActualValue;
+      return Cross(random, parent0, parent1, interpreter, problemData,
+                   rows, MaximumSymbolicExpressionTreeDepth.Value, MaximumSymbolicExpressionTreeLength.Value);
+    }
+
+    /// <summary>
+    /// Takes two parent individuals P0 and P1. 
+    /// Randomly choose a node i from the first parent, then for each matching node j from the second parent, calculate the behavioral distance based on the range:
+    /// d(i,j) = 0.5 * ( abs(max(i) - max(j)) + abs(min(i) - min(j)) ).
+    /// Next, assign probabilities for the selection of a node j based on the inversed and normalized behavioral distance, then make a random weighted choice.
+    /// </summary>
+    public static ISymbolicExpressionTree Cross(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1,
+                                                ISymbolicDataAnalysisExpressionTreeInterpreter interpreter, T problemData, IList<int> rows, int maxDepth, int maxLength) {
+      var crossoverPoints0 = new List<CutPoint>();
+      parent0.Root.ForEachNodePostfix((n) => {
+        // the if clauses prevent the root or the startnode from being selected, although the startnode can be the parent of the node being swapped.
+        if (n.Parent != null && n.Parent != parent0.Root) {
+          crossoverPoints0.Add(new CutPoint(n.Parent, n));
+        }
+      });
+
+      var crossoverPoint0 = crossoverPoints0.SampleRandom(random);
+      int level = parent0.Root.GetBranchLevel(crossoverPoint0.Child);
+      int length = parent0.Root.GetLength() - crossoverPoint0.Child.GetLength();
+
+      var allowedBranches = new List<ISymbolicExpressionTreeNode>();
+      parent1.Root.ForEachNodePostfix((n) => {
+        if (n.Parent != null && n.Parent != parent1.Root) {
+          if (n.GetDepth() + level <= maxDepth && n.GetLength() + length <= maxLength && crossoverPoint0.IsMatchingPointType(n))
+            allowedBranches.Add(n);
+        }
+      });
+
+      if (allowedBranches.Count == 0)
+        return parent0;
+
+      var dataset = problemData.Dataset;
+
+      // create symbols in order to improvize an ad-hoc tree so that the child can be evaluated
+      var rootSymbol = new ProgramRootSymbol();
+      var startSymbol = new StartSymbol();
+      var tree0 = CreateTreeFromNode(random, crossoverPoint0.Child, rootSymbol, startSymbol); // this will change crossoverPoint0.Child.Parent
+      double min0 = 0.0, max0 = 0.0;
+      foreach (double v in interpreter.GetSymbolicExpressionTreeValues(tree0, dataset, rows)) {
+        if (min0 > v) min0 = v;
+        if (max0 < v) max0 = v;
+      }
+      crossoverPoint0.Child.Parent = crossoverPoint0.Parent; // restore correct parent 
+
+      var weights = new List<double>();
+      foreach (var node in allowedBranches) {
+        var parent = node.Parent;
+        var tree1 = CreateTreeFromNode(random, node, rootSymbol, startSymbol);
+        double min1 = 0.0, max1 = 0.0;
+        foreach (double v in interpreter.GetSymbolicExpressionTreeValues(tree1, dataset, rows)) {
+          if (min1 > v) min1 = v;
+          if (max1 < v) max1 = v;
+        }
+        double behavioralDistance = (Math.Abs(min0 - min1) + Math.Abs(max0 - max1)) / 2; // this can be NaN of Infinity because some trees are crazy like exp(exp(exp(...))), we correct that below
+        weights.Add(behavioralDistance);
+        node.Parent = parent; // restore correct node parent
+      }
+
+      // remove branches with an infinite or NaN behavioral distance
+      for (int i = weights.Count - 1; i >= 0; --i) {
+        if (Double.IsNaN(weights[i]) || Double.IsInfinity(weights[i])) {
+          weights.RemoveAt(i);
+          allowedBranches.RemoveAt(i);
+        }
+      }
+      // check if there are any allowed branches left
+      if (allowedBranches.Count == 0)
+        return parent0;
+
+      ISymbolicExpressionTreeNode selectedBranch;
+      double sum = weights.Sum();
+
+      if (sum.IsAlmost(0.0) || weights.Count == 1) // if there is only one allowed branch, or if all weights are zero
+        selectedBranch = allowedBranches[0];
+      else {
+        for (int i = 0; i != weights.Count; ++i) // normalize and invert values
+          weights[i] = 1 - weights[i] / sum;
+
+        sum = weights.Sum(); // take new sum
+
+        // compute the probabilities (selection weights)
+        for (int i = 0; i != weights.Count; ++i)
+          weights[i] /= sum;
+
+#pragma warning disable 612, 618
+        selectedBranch = allowedBranches.SelectRandom(weights, random);
+#pragma warning restore 612, 618
+      }
+      Swap(crossoverPoint0, selectedBranch);
+      return parent0;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionSemanticSimilarityCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionSemanticSimilarityCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Crossovers/SymbolicDataAnalysisExpressionSemanticSimilarityCrossover.cs	(revision 16337)
@@ -0,0 +1,133 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("SemanticSimilarityCrossover", "An operator which performs subtree swapping based on the notion semantic similarity between subtrees\n" +
+                                       "(criteria: mean of the absolute differences between the estimated output values of the two subtrees, falling into a user-defined range)\n" +
+                                       "- Take two parent individuals P0 and P1\n" +
+                                       "- Randomly choose a node N from the P0\n" +
+                                       "- Find the first node M that satisfies the semantic similarity criteria\n" +
+                                       "- Swap N for M and return P0")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionSemanticSimilarityCrossover<T> : SymbolicDataAnalysisExpressionCrossover<T> where T : class, IDataAnalysisProblemData {
+    private const string SemanticSimilarityRangeParameterName = "SemanticSimilarityRange";
+
+    #region Parameter properties
+    public IValueParameter<DoubleRange> SemanticSimilarityRangeParameter {
+      get { return (IValueParameter<DoubleRange>)Parameters[SemanticSimilarityRangeParameterName]; }
+    }
+    #endregion
+
+    #region Properties
+    public DoubleRange SemanticSimilarityRange {
+      get { return SemanticSimilarityRangeParameter.Value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionSemanticSimilarityCrossover(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionSemanticSimilarityCrossover(SymbolicDataAnalysisExpressionCrossover<T> original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisExpressionSemanticSimilarityCrossover()
+      : base() {
+      Parameters.Add(new ValueLookupParameter<DoubleRange>(SemanticSimilarityRangeParameterName, "Semantic similarity interval.", new DoubleRange(0.0001, 10)));
+      name = "SemanticSimilarityCrossover";
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionSemanticSimilarityCrossover<T>(this, cloner);
+    }
+
+    public override ISymbolicExpressionTree Crossover(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1) {
+      ISymbolicDataAnalysisExpressionTreeInterpreter interpreter = SymbolicDataAnalysisTreeInterpreterParameter.ActualValue;
+      List<int> rows = GenerateRowsToEvaluate().ToList();
+      T problemData = ProblemDataParameter.ActualValue;
+      return Cross(random, parent0, parent1, interpreter, problemData, rows, MaximumSymbolicExpressionTreeDepth.Value, MaximumSymbolicExpressionTreeLength.Value, SemanticSimilarityRange);
+    }
+
+    /// <summary>
+    /// Takes two parent individuals P0 and P1. 
+    /// Randomly choose a node i from the first parent, then get a node j from the second parent that matches the semantic similarity criteria.
+    /// </summary>
+    public static ISymbolicExpressionTree Cross(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1, ISymbolicDataAnalysisExpressionTreeInterpreter interpreter,
+                                                T problemData, List<int> rows, int maxDepth, int maxLength, DoubleRange range) {
+      var crossoverPoints0 = new List<CutPoint>();
+      parent0.Root.ForEachNodePostfix((n) => {
+        if (n.Parent != null && n.Parent != parent0.Root)
+          crossoverPoints0.Add(new CutPoint(n.Parent, n));
+      });
+
+      var crossoverPoint0 = crossoverPoints0.SampleRandom(random);
+      int level = parent0.Root.GetBranchLevel(crossoverPoint0.Child);
+      int length = parent0.Root.GetLength() - crossoverPoint0.Child.GetLength();
+
+      var allowedBranches = new List<ISymbolicExpressionTreeNode>();
+      parent1.Root.ForEachNodePostfix((n) => {
+        if (n.Parent != null && n.Parent != parent1.Root) {
+          if (n.GetDepth() + level <= maxDepth && n.GetLength() + length <= maxLength && crossoverPoint0.IsMatchingPointType(n))
+            allowedBranches.Add(n);
+        }
+      });
+
+      if (allowedBranches.Count == 0)
+        return parent0;
+
+      var dataset = problemData.Dataset;
+
+      // create symbols in order to improvize an ad-hoc tree so that the child can be evaluated
+      var rootSymbol = new ProgramRootSymbol();
+      var startSymbol = new StartSymbol();
+      var tree0 = CreateTreeFromNode(random, crossoverPoint0.Child, rootSymbol, startSymbol);
+      List<double> estimatedValues0 = interpreter.GetSymbolicExpressionTreeValues(tree0, dataset, rows).ToList();
+      crossoverPoint0.Child.Parent = crossoverPoint0.Parent; // restore parent
+      ISymbolicExpressionTreeNode selectedBranch = null;
+
+      // pick the first node that fulfills the semantic similarity conditions
+      foreach (var node in allowedBranches) {
+        var parent = node.Parent;
+        var tree1 = CreateTreeFromNode(random, node, startSymbol, rootSymbol); // this will affect node.Parent 
+        List<double> estimatedValues1 = interpreter.GetSymbolicExpressionTreeValues(tree1, dataset, rows).ToList();
+        node.Parent = parent; // restore parent
+
+        OnlineCalculatorError errorState;
+        double ssd = OnlineMeanAbsoluteErrorCalculator.Calculate(estimatedValues0, estimatedValues1, out errorState);
+
+        if (range.Start <= ssd && ssd <= range.End) {
+          selectedBranch = node;
+          break;
+        }
+      }
+
+      // perform the actual swap
+      if (selectedBranch != null)
+        Swap(crossoverPoint0, selectedBranch);
+      return parent0;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisEvaluator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisEvaluator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisEvaluator.cs	(revision 16337)
@@ -0,0 +1,189 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Operators;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisEvaluator<T> : InstrumentedOperator,
+    ISymbolicDataAnalysisEvaluator<T>, ISymbolicDataAnalysisInterpreterOperator, ISymbolicDataAnalysisBoundedOperator, IStochasticOperator
+  where T : class, IDataAnalysisProblemData {
+    private const string RandomParameterName = "Random";
+    private const string SymbolicExpressionTreeParameterName = "SymbolicExpressionTree";
+    private const string SymbolicDataAnalysisTreeInterpreterParameterName = "SymbolicExpressionTreeInterpreter";
+    private const string ProblemDataParameterName = "ProblemData";
+    private const string EstimationLimitsParameterName = "EstimationLimits";
+    private const string EvaluationPartitionParameterName = "EvaluationPartition";
+    private const string RelativeNumberOfEvaluatedSamplesParameterName = "RelativeNumberOfEvaluatedSamples";
+    private const string ApplyLinearScalingParameterName = "ApplyLinearScaling";
+    private const string ValidRowIndicatorParameterName = "ValidRowIndicator";
+
+    public override bool CanChangeName { get { return false; } }
+
+    #region parameter properties
+    ILookupParameter<IRandom> IStochasticOperator.RandomParameter {
+      get { return RandomParameter; }
+    }
+
+    public IValueLookupParameter<IRandom> RandomParameter {
+      get { return (IValueLookupParameter<IRandom>)Parameters[RandomParameterName]; }
+    }
+    public ILookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter {
+      get { return (ILookupParameter<ISymbolicExpressionTree>)Parameters[SymbolicExpressionTreeParameterName]; }
+    }
+    public ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicDataAnalysisTreeInterpreterParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>)Parameters[SymbolicDataAnalysisTreeInterpreterParameterName]; }
+    }
+    public IValueLookupParameter<T> ProblemDataParameter {
+      get { return (IValueLookupParameter<T>)Parameters[ProblemDataParameterName]; }
+    }
+
+    public IValueLookupParameter<IntRange> EvaluationPartitionParameter {
+      get { return (IValueLookupParameter<IntRange>)Parameters[EvaluationPartitionParameterName]; }
+    }
+    public IValueLookupParameter<DoubleLimit> EstimationLimitsParameter {
+      get { return (IValueLookupParameter<DoubleLimit>)Parameters[EstimationLimitsParameterName]; }
+    }
+    public IValueLookupParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter {
+      get { return (IValueLookupParameter<PercentValue>)Parameters[RelativeNumberOfEvaluatedSamplesParameterName]; }
+    }
+    public ILookupParameter<BoolValue> ApplyLinearScalingParameter {
+      get { return (ILookupParameter<BoolValue>)Parameters[ApplyLinearScalingParameterName]; }
+    }
+    public IValueLookupParameter<StringValue> ValidRowIndicatorParameter {
+      get { return (IValueLookupParameter<StringValue>)Parameters[ValidRowIndicatorParameterName]; }
+    }
+    #endregion
+
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisEvaluator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisEvaluator(SymbolicDataAnalysisEvaluator<T> original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public SymbolicDataAnalysisEvaluator()
+      : base() {
+      Parameters.Add(new ValueLookupParameter<IRandom>(RandomParameterName, "The random generator to use.") { Hidden = true });
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>(SymbolicDataAnalysisTreeInterpreterParameterName, "The interpreter that should be used to calculate the output values of the symbolic data analysis tree.") { Hidden = true });
+      Parameters.Add(new LookupParameter<ISymbolicExpressionTree>(SymbolicExpressionTreeParameterName, "The symbolic data analysis solution encoded as a symbolic expression tree.") { Hidden = true });
+      Parameters.Add(new ValueLookupParameter<T>(ProblemDataParameterName, "The problem data on which the symbolic data analysis solution should be evaluated.") { Hidden = true });
+      Parameters.Add(new ValueLookupParameter<IntRange>(EvaluationPartitionParameterName, "The start index of the dataset partition on which the symbolic data analysis solution should be evaluated.") { Hidden = true });
+      Parameters.Add(new ValueLookupParameter<DoubleLimit>(EstimationLimitsParameterName, "The upper and lower limit that should be used as cut off value for the output values of symbolic data analysis trees.") { Hidden = true });
+      Parameters.Add(new ValueLookupParameter<PercentValue>(RelativeNumberOfEvaluatedSamplesParameterName, "The relative number of samples of the dataset partition, which should be randomly chosen for evaluation between the start and end index.") { Hidden = true });
+      Parameters.Add(new LookupParameter<BoolValue>(ApplyLinearScalingParameterName, "Flag that indicates if the individual should be linearly scaled before evaluating.") { Hidden = true });
+      Parameters.Add(new ValueLookupParameter<StringValue>(ValidRowIndicatorParameterName, "An indicator variable in the data set that specifies which rows should be evaluated (those for which the indicator <> 0) (optional).") { Hidden = true });
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (Parameters.ContainsKey(ApplyLinearScalingParameterName) && !(Parameters[ApplyLinearScalingParameterName] is LookupParameter<BoolValue>))
+        Parameters.Remove(ApplyLinearScalingParameterName);
+      if (!Parameters.ContainsKey(ApplyLinearScalingParameterName))
+        Parameters.Add(new LookupParameter<BoolValue>(ApplyLinearScalingParameterName, "Flag that indicates if the individual should be linearly scaled before evaluating."));
+      if (!Parameters.ContainsKey(ValidRowIndicatorParameterName))
+        Parameters.Add(new ValueLookupParameter<StringValue>(ValidRowIndicatorParameterName, "An indicator variable in the data set that specifies which rows should be evaluated (those for which the indicator <> 0) (optional)."));
+    }
+
+    protected IEnumerable<int> GenerateRowsToEvaluate() {
+      return GenerateRowsToEvaluate(RelativeNumberOfEvaluatedSamplesParameter.ActualValue.Value);
+    }
+
+    protected IEnumerable<int> GenerateRowsToEvaluate(double percentageOfRows) {
+      IEnumerable<int> rows;
+      int samplesStart = EvaluationPartitionParameter.ActualValue.Start;
+      int samplesEnd = EvaluationPartitionParameter.ActualValue.End;
+      int testPartitionStart = ProblemDataParameter.ActualValue.TestPartition.Start;
+      int testPartitionEnd = ProblemDataParameter.ActualValue.TestPartition.End;
+      if (samplesEnd < samplesStart) throw new ArgumentException("Start value is larger than end value.");
+
+      if (percentageOfRows.IsAlmost(1.0))
+        rows = Enumerable.Range(samplesStart, samplesEnd - samplesStart);
+      else {
+        int seed = RandomParameter.ActualValue.Next();
+        int count = (int)((samplesEnd - samplesStart) * percentageOfRows);
+        if (count == 0) count = 1;
+        rows = RandomEnumerable.SampleRandomNumbers(seed, samplesStart, samplesEnd, count);
+      }
+
+      rows = rows.Where(i => i < testPartitionStart || testPartitionEnd <= i);
+      if (ValidRowIndicatorParameter.ActualValue != null) {
+        string indicatorVar = ValidRowIndicatorParameter.ActualValue.Value;
+        var problemData = ProblemDataParameter.ActualValue;
+        var indicatorRow = problemData.Dataset.GetReadOnlyDoubleValues(indicatorVar);
+        rows = rows.Where(r => !indicatorRow[r].IsAlmost(0.0));
+      }
+      return rows;
+    }
+
+    [ThreadStatic]
+    private static double[] cache;
+    protected static void CalculateWithScaling(IEnumerable<double> targetValues, IEnumerable<double> estimatedValues,
+      double lowerEstimationLimit, double upperEstimationLimit,
+      IOnlineCalculator calculator, int maxRows) {
+      if (cache == null || cache.Length < maxRows) {
+        cache = new double[maxRows];
+      }
+
+      // calculate linear scaling
+      int i = 0;
+      var linearScalingCalculator = new OnlineLinearScalingParameterCalculator();
+      var targetValuesEnumerator = targetValues.GetEnumerator();
+      var estimatedValuesEnumerator = estimatedValues.GetEnumerator();
+      while (targetValuesEnumerator.MoveNext() & estimatedValuesEnumerator.MoveNext()) {
+        double target = targetValuesEnumerator.Current;
+        double estimated = estimatedValuesEnumerator.Current;
+        cache[i] = estimated;
+        if (!double.IsNaN(estimated) && !double.IsInfinity(estimated))
+          linearScalingCalculator.Add(estimated, target);
+        i++;
+      }
+      if (linearScalingCalculator.ErrorState == OnlineCalculatorError.None && (targetValuesEnumerator.MoveNext() || estimatedValuesEnumerator.MoveNext()))
+        throw new ArgumentException("Number of elements in target and estimated values enumeration do not match.");
+
+      double alpha = linearScalingCalculator.Alpha;
+      double beta = linearScalingCalculator.Beta;
+      if (linearScalingCalculator.ErrorState != OnlineCalculatorError.None) {
+        alpha = 0.0;
+        beta = 1.0;
+      }
+
+      //calculate the quality by using the passed online calculator
+      targetValuesEnumerator = targetValues.GetEnumerator();
+      var scaledBoundedEstimatedValuesEnumerator = Enumerable.Range(0, i).Select(x => cache[x] * beta + alpha)
+        .LimitToRange(lowerEstimationLimit, upperEstimationLimit).GetEnumerator();
+
+      while (targetValuesEnumerator.MoveNext() & scaledBoundedEstimatedValuesEnumerator.MoveNext()) {
+        calculator.Add(targetValuesEnumerator.Current, scaledBoundedEstimatedValuesEnumerator.Current);
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisMultiObjectiveEvaluator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisMultiObjectiveEvaluator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisMultiObjectiveEvaluator.cs	(revision 16337)
@@ -0,0 +1,54 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisMultiObjectiveEvaluator<T> : SymbolicDataAnalysisEvaluator<T>, ISymbolicDataAnalysisMultiObjectiveEvaluator<T>
+   where T : class, IDataAnalysisProblemData {
+    private const string QualitiesParameterName = "Qualities";
+    public ILookupParameter<DoubleArray> QualitiesParameter {
+      get { return (ILookupParameter<DoubleArray>)Parameters[QualitiesParameterName]; }
+    }
+
+    public abstract IEnumerable<bool> Maximization { get; }
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisMultiObjectiveEvaluator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisMultiObjectiveEvaluator(SymbolicDataAnalysisMultiObjectiveEvaluator<T> original, Cloner cloner)
+      : base(original, cloner) {
+    }
+
+    protected SymbolicDataAnalysisMultiObjectiveEvaluator()
+      : base() {
+      Parameters.Add(new LookupParameter<DoubleArray>(QualitiesParameterName, "The qualities of the evaluated symbolic data analysis solution."));
+    }
+
+    public abstract double[] Evaluate(IExecutionContext context, ISymbolicExpressionTree tree, T problemData, IEnumerable<int> rows);
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisSingleObjectiveEvaluator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisSingleObjectiveEvaluator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Evaluators/SymbolicDataAnalysisSingleObjectiveEvaluator.cs	(revision 16337)
@@ -0,0 +1,57 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using System.Collections.Generic;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisSingleObjectiveEvaluator<T> : SymbolicDataAnalysisEvaluator<T>, ISymbolicDataAnalysisSingleObjectiveEvaluator<T>
+   where T : class, IDataAnalysisProblemData {
+    private const string QualityParameterName = "Quality";
+    #region parameter properties
+    public ILookupParameter<DoubleValue> QualityParameter {
+      get { return (ILookupParameter<DoubleValue>)Parameters[QualityParameterName]; }
+    }
+    #endregion
+    #region properties
+    public abstract bool Maximization { get; }
+    #endregion
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectiveEvaluator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisSingleObjectiveEvaluator(SymbolicDataAnalysisSingleObjectiveEvaluator<T> original, Cloner cloner)
+      : base(original, cloner) {
+    }
+
+    protected SymbolicDataAnalysisSingleObjectiveEvaluator()
+      : base() {
+      Parameters.Add(new LookupParameter<DoubleValue>(QualityParameterName, "The quality of the evaluated symbolic data analysis solution."));
+    }
+
+    public abstract double Evaluate(IExecutionContext context, ISymbolicExpressionTree tree, T problemData, IEnumerable<int> rows);
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/InfixExpressionFormatter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/InfixExpressionFormatter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/InfixExpressionFormatter.cs	(revision 16337)
@@ -0,0 +1,192 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Formats mathematical expressions in infix form. E.g. x1 * (3.0 * x2 + x3)
+  /// </summary>
+  [StorableClass]
+  [Item("Infix Symbolic Expression Tree Formatter", "A string formatter that converts symbolic expression trees to infix expressions.")]
+
+  public sealed class InfixExpressionFormatter : NamedItem, ISymbolicExpressionTreeStringFormatter {
+
+
+    [StorableConstructor]
+    private InfixExpressionFormatter(bool deserializing) : base(deserializing) { }
+    private InfixExpressionFormatter(InfixExpressionFormatter original, Cloner cloner) : base(original, cloner) { }
+    public InfixExpressionFormatter()
+      : base() {
+      Name = ItemName;
+      Description = ItemDescription;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new InfixExpressionFormatter(this, cloner);
+    }
+
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree) {
+      // skip root and start symbols
+      StringBuilder strBuilder = new StringBuilder();
+      FormatRecursively(symbolicExpressionTree.Root.GetSubtree(0).GetSubtree(0), strBuilder);
+      return strBuilder.ToString();
+    }
+
+    private void FormatRecursively(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.SubtreeCount > 1) {
+        var token = GetToken(node.Symbol);
+        if (token == "+" || token == "-" || token == "OR" || token == "XOR") {
+          strBuilder.Append("(");
+          FormatRecursively(node.Subtrees.First(), strBuilder);
+
+          foreach (var subtree in node.Subtrees.Skip(1)) {
+            strBuilder.Append(" ").Append(token).Append(" ");
+            FormatRecursively(subtree, strBuilder);
+          }
+          strBuilder.Append(")");
+
+        } else if (token == "*" || token == "/" || token == "AND") {
+          strBuilder.Append("(");
+          FormatRecursively(node.Subtrees.First(), strBuilder);
+
+          foreach (var subtree in node.Subtrees.Skip(1)) {
+            strBuilder.Append(" ").Append(token).Append(" ");
+            FormatRecursively(subtree, strBuilder);
+          }
+          strBuilder.Append(")");
+        } else {
+          // function with multiple arguments
+          strBuilder.Append(token).Append("(");
+          FormatRecursively(node.Subtrees.First(), strBuilder);
+          foreach (var subtree in node.Subtrees.Skip(1)) {
+            strBuilder.Append(", ");
+            FormatRecursively(subtree, strBuilder);
+          }
+          strBuilder.Append(")");
+        }
+      } else if (node.SubtreeCount == 1) {
+        var token = GetToken(node.Symbol);
+        if (token == "-" || token == "NOT") {
+          strBuilder.Append("(").Append(token).Append("(");
+          FormatRecursively(node.GetSubtree(0), strBuilder);
+          strBuilder.Append("))");
+        } else if (token == "/") {
+          strBuilder.Append("1/");
+          FormatRecursively(node.GetSubtree(0), strBuilder);
+        } else if (token == "+" || token == "*") {
+          FormatRecursively(node.GetSubtree(0), strBuilder);
+        } else {
+          // function with only one argument
+          strBuilder.Append(token).Append("(");
+          FormatRecursively(node.GetSubtree(0), strBuilder);
+          strBuilder.Append(")");
+        }
+      } else {
+        // no subtrees
+        if (node.Symbol is LaggedVariable) {
+          var varNode = node as LaggedVariableTreeNode;
+          if (!varNode.Weight.IsAlmost(1.0)) {
+            strBuilder.Append("(");
+            strBuilder.AppendFormat(CultureInfo.InvariantCulture, "{0}", varNode.Weight);
+            strBuilder.Append("*");
+          }
+          strBuilder.Append("LAG(");
+          if (varNode.VariableName.Contains("'")) {
+            strBuilder.AppendFormat("\"{0}\"", varNode.VariableName);
+          } else {
+            strBuilder.AppendFormat("'{0}'", varNode.VariableName);
+          }
+          strBuilder.Append(", ")
+            .AppendFormat(CultureInfo.InvariantCulture, "{0}", varNode.Lag)
+            .Append(")");
+        } else if (node.Symbol is Variable) {
+          var varNode = node as VariableTreeNode;
+          if (!varNode.Weight.IsAlmost(1.0)) {
+            strBuilder.Append("(");
+            strBuilder.AppendFormat(CultureInfo.InvariantCulture, "{0}", varNode.Weight);
+            strBuilder.Append("*");
+          }
+          if (varNode.VariableName.Contains("'")) {
+            strBuilder.AppendFormat("\"{0}\"", varNode.VariableName);
+          } else {
+            strBuilder.AppendFormat("'{0}'", varNode.VariableName);
+          }
+          if (!varNode.Weight.IsAlmost(1.0)) {
+            strBuilder.Append(")");
+          }
+        } else if (node.Symbol is FactorVariable) {
+          var factorNode = node as FactorVariableTreeNode;
+          if (factorNode.VariableName.Contains("'")) {
+            strBuilder.AppendFormat("\"{0}\"", factorNode.VariableName);
+          } else {
+            strBuilder.AppendFormat("'{0}'", factorNode.VariableName);
+          }
+          strBuilder.AppendFormat("[{0}]",
+            string.Join(", ", factorNode.Weights.Select(w => w.ToString(CultureInfo.InvariantCulture))));
+        } else if (node.Symbol is BinaryFactorVariable) {
+          var factorNode = node as BinaryFactorVariableTreeNode;
+          if (!factorNode.Weight.IsAlmost(1.0)) {
+            strBuilder.Append("(");
+            strBuilder.AppendFormat(CultureInfo.InvariantCulture, "{0}", factorNode.Weight);
+            strBuilder.Append("*");
+          }
+          if (factorNode.VariableName.Contains("'")) {
+            strBuilder.AppendFormat("\"{0}\"", factorNode.VariableName);
+          } else {
+            strBuilder.AppendFormat("'{0}'", factorNode.VariableName);
+          }
+          strBuilder.Append(" = ");
+          if (factorNode.VariableValue.Contains("'")) {
+            strBuilder.AppendFormat("\"{0}\"", factorNode.VariableValue);
+          } else {
+            strBuilder.AppendFormat("'{0}'", factorNode.VariableValue);
+          }
+
+          if (!factorNode.Weight.IsAlmost(1.0)) {
+            strBuilder.Append(")");
+          }
+
+        } else if (node.Symbol is Constant) {
+          var constNode = node as ConstantTreeNode;
+          if (constNode.Value >= 0.0)
+            strBuilder.AppendFormat(CultureInfo.InvariantCulture, "{0}", constNode.Value);
+          else
+            strBuilder.AppendFormat(CultureInfo.InvariantCulture, "({0})", constNode.Value); // (-1
+        }
+      }
+    }
+
+    private string GetToken(ISymbol symbol) {
+      var tok = InfixExpressionParser.knownSymbols.GetBySecond(symbol).SingleOrDefault();
+      if (tok == null)
+        throw new ArgumentException(string.Format("Unknown symbol {0} found.", symbol.Name));
+      return tok;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionCSharpFormatter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionCSharpFormatter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionCSharpFormatter.cs	(revision 16337)
@@ -0,0 +1,302 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using System.Text.RegularExpressions;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("C# Symbolic Expression Tree Formatter", "A string formatter that converts symbolic expression trees to C# code.")]
+  [StorableClass]
+  public sealed class CSharpSymbolicExpressionTreeStringFormatter : NamedItem, ISymbolicExpressionTreeStringFormatter {
+    [StorableConstructor]
+    private CSharpSymbolicExpressionTreeStringFormatter(bool deserializing) : base(deserializing) { }
+    private CSharpSymbolicExpressionTreeStringFormatter(CSharpSymbolicExpressionTreeStringFormatter original, Cloner cloner) : base(original, cloner) { }
+    public CSharpSymbolicExpressionTreeStringFormatter()
+      : base() {
+      Name = ItemName;
+      Description = ItemDescription;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new CSharpSymbolicExpressionTreeStringFormatter(this, cloner);
+    }
+
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree) {
+      // skip root and start symbols
+      StringBuilder strBuilder = new StringBuilder();
+      GenerateHeader(strBuilder, symbolicExpressionTree);
+      FormatRecursively(symbolicExpressionTree.Root.GetSubtree(0).GetSubtree(0), strBuilder);
+      GenerateFooter(strBuilder);
+      return strBuilder.ToString();
+    }
+
+    private string VariableName2Identifier(string name) {     
+      /*
+       * identifier-start-character:
+       *    letter-character
+       *    _ (the underscore character U+005F)
+       *  identifier-part-characters:
+       *    identifier-part-character
+       *    identifier-part-characters   identifier-part-character
+       *  identifier-part-character:
+       *    letter-character
+       *    decimal-digit-character
+       *    connecting-character
+       *    combining-character
+       *    formatting-character
+       *  letter-character:
+       *    A Unicode character of classes Lu, Ll, Lt, Lm, Lo, or Nl 
+       *    A unicode-escape-sequence representing a character of classes Lu, Ll, Lt, Lm, Lo, or Nl
+       *  combining-character:
+       *    A Unicode character of classes Mn or Mc 
+       *    A unicode-escape-sequence representing a character of classes Mn or Mc
+       *  decimal-digit-character:
+       *    A Unicode character of the class Nd 
+       *    A unicode-escape-sequence representing a character of the class Nd
+       *  connecting-character:
+       *    A Unicode character of the class Pc 
+       *    A unicode-escape-sequence representing a character of the class Pc
+       *  formatting-character:
+       *    A Unicode character of the class Cf 
+       *    A unicode-escape-sequence representing a character of the class Cf
+       */
+
+      var invalidIdentifierStarts = new Regex(@"[^_\p{Lu}\p{Ll}\p{Lt}\p{Lm}\p{Lo}\p{Nl}]");
+      var invalidIdentifierParts = new Regex(@"[^\p{Lu}\p{Ll}\p{Lt}\p{Lm}\p{Lo}\p{Nl}\p{Mn}\p{Mc}\p{Nd}\p{Pc}\p{Cf}]");
+      return "@" +
+        (invalidIdentifierStarts.IsMatch(name.Substring(0, 1)) ? "_" : "") + // prepend '_' if necessary
+        invalidIdentifierParts.Replace(name, "_");
+    }
+
+    private void FormatRecursively(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      // TODO: adapt to interpreter semantics. The HL interpreter also allows Boolean operations on reals
+      if (node.Subtrees.Any()) {
+        if (node.Symbol is Addition) {
+          FormatOperator(node, "+", strBuilder);
+        } else if (node.Symbol is And) {
+          FormatOperator(node, "&&", strBuilder);
+        } else if (node.Symbol is Average) {
+          FormatFunction(node, "Average", strBuilder);
+        } else if (node.Symbol is Cosine) {
+          FormatFunction(node, "Math.Cos", strBuilder);
+        } else if (node.Symbol is Division) {
+          FormatDivision(node, strBuilder);
+        } else if (node.Symbol is Exponential) {
+          FormatFunction(node, "Math.Exp", strBuilder);
+        } else if (node.Symbol is GreaterThan) {
+          FormatOperator(node, ">", strBuilder);
+        } else if (node.Symbol is IfThenElse) {
+          FormatFunction(node, "EvaluateIf", strBuilder);
+        } else if (node.Symbol is LessThan) {
+          FormatOperator(node, "<", strBuilder);
+        } else if (node.Symbol is Logarithm) {
+          FormatFunction(node, "Math.Log", strBuilder);
+        } else if (node.Symbol is Multiplication) {
+          FormatOperator(node, "*", strBuilder);
+        } else if (node.Symbol is Not) {
+          FormatOperator(node, "!", strBuilder);
+        } else if (node.Symbol is Or) {
+          FormatOperator(node, "||", strBuilder);
+        } else if (node.Symbol is Xor) {
+          FormatOperator(node, "^", strBuilder);
+        } else if (node.Symbol is Sine) {
+          FormatFunction(node, "Math.Sin", strBuilder);
+        } else if (node.Symbol is Subtraction) {
+          FormatSubtraction(node, strBuilder);
+        } else if (node.Symbol is Tangent) {
+          FormatFunction(node, "Math.Tan", strBuilder);
+        } else if (node.Symbol is Square) {
+          FormatSquare(node, strBuilder);
+        } else if (node.Symbol is SquareRoot) {
+          FormatFunction(node, "Math.Sqrt", strBuilder);
+        } else if (node.Symbol is Power) {
+          FormatFunction(node, "Math.Pow", strBuilder);
+        } else if (node.Symbol is Root) {
+          FormatRoot(node, strBuilder);
+        } else {
+          throw new NotSupportedException("Formatting of symbol: " + node.Symbol + " not supported for C# symbolic expression tree formatter.");
+        }
+      } else {
+        if (node is VariableTreeNode) {
+          var varNode = node as VariableTreeNode;
+          strBuilder.AppendFormat("{0} * {1}", VariableName2Identifier(varNode.VariableName), varNode.Weight.ToString("g17", CultureInfo.InvariantCulture));
+        } else if (node is ConstantTreeNode) {
+          var constNode = node as ConstantTreeNode;
+          strBuilder.Append(constNode.Value.ToString("g17", CultureInfo.InvariantCulture));
+        } else if (node.Symbol is FactorVariable) {
+          var factorNode = node as FactorVariableTreeNode;
+          FormatFactor(factorNode, strBuilder);
+        } else if (node.Symbol is BinaryFactorVariable) {
+          var binFactorNode = node as BinaryFactorVariableTreeNode;
+          FormatBinaryFactor(binFactorNode, strBuilder);
+        } else {
+          throw new NotSupportedException("Formatting of symbol: " + node.Symbol + " not supported for C# symbolic expression tree formatter.");
+        }
+      }
+    }
+
+    private void FormatFactor(FactorVariableTreeNode node, StringBuilder strBuilder) {
+      strBuilder.AppendFormat("EvaluateFactor({0}, new [] {{ {1} }}, new [] {{ {2} }})", VariableName2Identifier(node.VariableName),
+        string.Join(",", node.Symbol.GetVariableValues(node.VariableName).Select(name => "\"" + name + "\"")), string.Join(",", node.Weights.Select(v => v.ToString(CultureInfo.InvariantCulture))));
+    }
+
+    private void FormatBinaryFactor(BinaryFactorVariableTreeNode node, StringBuilder strBuilder) {
+      strBuilder.AppendFormat(CultureInfo.InvariantCulture, "EvaluateBinaryFactor({0}, \"{1}\", {2})", VariableName2Identifier(node.VariableName), node.VariableValue, node.Weight);
+    }
+
+    private void FormatSquare(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("Math.Pow(");
+      FormatRecursively(node.GetSubtree(0), strBuilder);
+      strBuilder.Append(", 2)");
+    }
+
+    private void FormatRoot(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("Math.Pow(");
+      FormatRecursively(node.GetSubtree(0), strBuilder);
+      strBuilder.Append(", 1.0 / (");
+      FormatRecursively(node.GetSubtree(1), strBuilder);
+      strBuilder.Append("))");
+    }
+
+    private void FormatDivision(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.SubtreeCount == 1) {
+        strBuilder.Append("1.0 / ");
+        FormatRecursively(node.GetSubtree(0), strBuilder);
+      } else {
+        FormatRecursively(node.GetSubtree(0), strBuilder);
+        strBuilder.Append("/ (");
+        for (int i = 1; i < node.SubtreeCount; i++) {
+          if (i > 1) strBuilder.Append(" * ");
+          FormatRecursively(node.GetSubtree(i), strBuilder);
+        }
+        strBuilder.Append(")");
+      }
+    }
+
+    private void FormatSubtraction(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.SubtreeCount == 1) {
+        strBuilder.Append("-");
+        FormatRecursively(node.GetSubtree(0), strBuilder);
+        return;
+      }
+      //Default case: more than 1 child
+      FormatOperator(node, "-", strBuilder);
+    }
+
+    private void FormatOperator(ISymbolicExpressionTreeNode node, string symbol, StringBuilder strBuilder) {
+      strBuilder.Append("(");
+      foreach (var child in node.Subtrees) {
+        FormatRecursively(child, strBuilder);
+        if (child != node.Subtrees.Last())
+          strBuilder.Append(" " + symbol + " ");
+      }
+      strBuilder.Append(")");
+    }
+
+    private void FormatFunction(ISymbolicExpressionTreeNode node, string function, StringBuilder strBuilder) {
+      strBuilder.Append(function + "(");
+      foreach (var child in node.Subtrees) {
+        FormatRecursively(child, strBuilder);
+        if (child != node.Subtrees.Last())
+          strBuilder.Append(", ");
+      }
+      strBuilder.Append(")");
+    }
+
+    private void GenerateHeader(StringBuilder strBuilder, ISymbolicExpressionTree symbolicExpressionTree) {
+      strBuilder.AppendLine("using System;");
+      strBuilder.AppendLine("using System.Linq;" + Environment.NewLine);
+      strBuilder.AppendLine("namespace HeuristicLab.Models {");
+      strBuilder.AppendLine("public static class Model {");
+      GenerateAverageSource(strBuilder);
+      GenerateIfThenElseSource(strBuilder);
+      GenerateFactorSource(strBuilder);
+      GenerateBinaryFactorSource(strBuilder);
+      strBuilder.Append(Environment.NewLine + "public static double Evaluate (");
+
+      // here we don't have access to problemData to determine the type for each variable (double/string) therefore we must distinguish based on the symbol type
+      HashSet<string> doubleVarNames = new HashSet<string>();
+      foreach (var node in symbolicExpressionTree.IterateNodesPostfix().Where(x => x is VariableTreeNode || x is VariableConditionTreeNode)) {
+        doubleVarNames.Add(((IVariableTreeNode)node).VariableName);
+      }
+
+      HashSet<string> stringVarNames = new HashSet<string>();
+      foreach (var node in symbolicExpressionTree.IterateNodesPostfix().Where(x => x is BinaryFactorVariableTreeNode || x is FactorVariableTreeNode)) {
+        stringVarNames.Add(((IVariableTreeNode)node).VariableName);
+      }
+
+      var orderedNames = stringVarNames.OrderBy(n => n, new NaturalStringComparer()).Select(n => "string " + VariableName2Identifier(n) + " /* " + n + " */");
+      strBuilder.Append(string.Join(", ", orderedNames));
+
+      if (stringVarNames.Any() && doubleVarNames.Any())
+        strBuilder.AppendLine(",");
+      orderedNames = doubleVarNames.OrderBy(n => n, new NaturalStringComparer()).Select(n => "double " + VariableName2Identifier(n) + " /* " + n + " */");
+      strBuilder.Append(string.Join(", ", orderedNames));
+
+
+      strBuilder.AppendLine(") {");
+      strBuilder.Append("double result = ");
+    }
+
+    private void GenerateFooter(StringBuilder strBuilder) {
+      strBuilder.AppendLine(";");
+
+      strBuilder.AppendLine("return result;");
+      strBuilder.AppendLine("}");
+      strBuilder.AppendLine("}");
+      strBuilder.AppendLine("}");
+    }
+
+    private void GenerateAverageSource(StringBuilder strBuilder) {
+      strBuilder.AppendLine("private static double Average(params double[] values) {");
+      strBuilder.AppendLine("  return values.Average();");
+      strBuilder.AppendLine("}");
+    }
+
+    private void GenerateIfThenElseSource(StringBuilder strBuilder) {
+      strBuilder.AppendLine("private static double EvaluateIf(bool condition, double then, double @else) {");
+      strBuilder.AppendLine("   return condition ? then : @else;");
+      strBuilder.AppendLine("}");
+    }
+
+    private void GenerateFactorSource(StringBuilder strBuilder) {
+      strBuilder.AppendLine("private static double EvaluateFactor(string factorValue, string[] factorValues, double[] constants) {");
+      strBuilder.AppendLine("   for(int i=0;i<factorValues.Length;i++) " +
+                            "      if(factorValues[i] == factorValue) return constants[i];" +
+                            "   throw new ArgumentException();");
+      strBuilder.AppendLine("}");
+    }
+
+    private void GenerateBinaryFactorSource(StringBuilder strBuilder) {
+      strBuilder.AppendLine("private static double EvaluateBinaryFactor(string factorValue, string targetValue, double weight) {");
+      strBuilder.AppendLine("  return factorValue == targetValue ? weight : 0.0;");
+      strBuilder.AppendLine("}");
+    }
+
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionExcelFormatter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionExcelFormatter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionExcelFormatter.cs	(revision 16337)
@@ -0,0 +1,305 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("Excel String Formatter", "String formatter for string representations of symbolic data analysis expressions in Excel syntax.")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionExcelFormatter : NamedItem, ISymbolicExpressionTreeStringFormatter {
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionExcelFormatter(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionExcelFormatter(SymbolicDataAnalysisExpressionExcelFormatter original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisExpressionExcelFormatter()
+      : base() {
+      Name = ItemName;
+      Description = ItemDescription;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionExcelFormatter(this, cloner);
+    }
+    private string GetExcelColumnName(int columnNumber) {
+      int dividend = columnNumber;
+      string columnName = String.Empty;
+
+      while (dividend > 0) {
+        int modulo = (dividend - 1) % 26;
+        columnName = System.Convert.ToChar(65 + modulo) + columnName;
+        dividend = (int)((dividend - modulo) / 26);
+      }
+
+      return columnName;
+    }
+
+    private readonly Dictionary<string, string> variableNameMapping = new Dictionary<string, string>();
+    private int currentVariableIndex = 0;
+    private string GetColumnToVariableName(string varName) {
+      if (!variableNameMapping.ContainsKey(varName)) {
+        currentVariableIndex++;
+        variableNameMapping.Add(varName, GetExcelColumnName(currentVariableIndex));
+      }
+      return string.Format("${0}1", variableNameMapping[varName]);
+    }
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree) {
+      return Format(symbolicExpressionTree, null);
+    }
+
+
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree, IDataset dataset) {
+      if (dataset != null)
+        return FormatWithMapping(symbolicExpressionTree, CalculateVariableMapping(symbolicExpressionTree, dataset));
+      else return FormatWithMapping(symbolicExpressionTree, new Dictionary<string, string>());
+    }
+
+    public string FormatWithMapping(ISymbolicExpressionTree symbolicExpressionTree, Dictionary<string, string> variableNameMapping) {
+      foreach (var kvp in variableNameMapping) this.variableNameMapping.Add(kvp.Key, kvp.Value);
+      var stringBuilder = new StringBuilder();
+
+      stringBuilder.Append("=");
+      stringBuilder.Append(FormatRecursively(symbolicExpressionTree.Root));
+
+      foreach (var variable in this.variableNameMapping) {
+        stringBuilder.AppendLine();
+        stringBuilder.Append(variable.Key + " = " + variable.Value);
+      }
+      return stringBuilder.ToString();
+    }
+
+    private Dictionary<string, string> CalculateVariableMapping(ISymbolicExpressionTree tree, IDataset dataset) {
+      var mapping = new Dictionary<string, string>();
+      int inputIndex = 0;
+      var usedVariables = tree.IterateNodesPrefix().OfType<IVariableTreeNode>().Select(v => v.VariableName).Distinct().ToArray();
+      foreach (var variable in dataset.VariableNames) {
+        if (!usedVariables.Contains(variable)) continue;
+        inputIndex++;
+        mapping[variable] = GetExcelColumnName(inputIndex);
+      }
+      return mapping;
+    }
+
+    private string FormatRecursively(ISymbolicExpressionTreeNode node) {
+      ISymbol symbol = node.Symbol;
+      StringBuilder stringBuilder = new StringBuilder();
+
+      if (symbol is ProgramRootSymbol) {
+        stringBuilder.AppendLine(FormatRecursively(node.GetSubtree(0)));
+      } else if (symbol is StartSymbol)
+        return FormatRecursively(node.GetSubtree(0));
+      else if (symbol is Addition) {
+        stringBuilder.Append("(");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("+");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+        }
+        stringBuilder.Append(")");
+      } else if (symbol is Average) {
+        stringBuilder.Append("(1/");
+        stringBuilder.Append(node.SubtreeCount);
+        stringBuilder.Append(")*(");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("+");
+          stringBuilder.Append("(");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          stringBuilder.Append(")");
+        }
+        stringBuilder.Append(")");
+      } else if (symbol is Constant) {
+        ConstantTreeNode constantTreeNode = node as ConstantTreeNode;
+        stringBuilder.Append(constantTreeNode.Value.ToString(CultureInfo.InvariantCulture));
+      } else if (symbol is Cosine) {
+        stringBuilder.Append("COS(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Division) {
+        if (node.SubtreeCount == 1) {
+          stringBuilder.Append("1/");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        } else {
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+          stringBuilder.Append("/(");
+          for (int i = 1; i < node.SubtreeCount; i++) {
+            if (i > 1) stringBuilder.Append("*");
+            stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          }
+          stringBuilder.Append(")");
+        }
+      } else if (symbol is Exponential) {
+        stringBuilder.Append("EXP(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Square) {
+        stringBuilder.Append("POWER(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(",2)");
+      } else if (symbol is SquareRoot) {
+        stringBuilder.Append("SQRT(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Logarithm) {
+        stringBuilder.Append("LN(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Multiplication) {
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("*");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+        }
+      } else if (symbol is Sine) {
+        stringBuilder.Append("SIN(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Subtraction) {
+        stringBuilder.Append("(");
+        if (node.SubtreeCount == 1) {
+          stringBuilder.Append("-");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        } else {
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+          for (int i = 1; i < node.SubtreeCount; i++) {
+            stringBuilder.Append("-");
+            stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          }
+        }
+        stringBuilder.Append(")");
+      } else if (symbol is Tangent) {
+        stringBuilder.Append("TAN(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+
+      } else if (symbol is Variable) {
+        VariableTreeNode variableTreeNode = node as VariableTreeNode;
+        stringBuilder.Append(variableTreeNode.Weight.ToString(CultureInfo.InvariantCulture));
+        stringBuilder.Append("*");
+        stringBuilder.Append(GetColumnToVariableName(variableTreeNode.VariableName));
+      } else if (symbol is BinaryFactorVariable) {
+        var binFactorNode = node as BinaryFactorVariableTreeNode;
+        stringBuilder.AppendFormat("IF({0}=\"{1}\", {2}, 0)",
+          GetColumnToVariableName(binFactorNode.VariableName),
+          binFactorNode.VariableValue,
+          binFactorNode.Weight.ToString(CultureInfo.InvariantCulture)
+          );
+      } else if (symbol is FactorVariable) {
+        var factorNode = node as FactorVariableTreeNode;
+        var values = factorNode.Symbol.GetVariableValues(factorNode.VariableName).ToArray();
+        var w = factorNode.Weights;
+        // create nested if
+        for (int i = 0; i < values.Length; i++) {
+          stringBuilder.AppendFormat("IF({0}=\"{1}\", {2}, ",
+            GetColumnToVariableName(factorNode.VariableName),
+            values[i],
+            w[i].ToString(CultureInfo.InvariantCulture));
+        }
+        stringBuilder.Append("\"\""); // return empty string on unknown value
+        stringBuilder.Append(')', values.Length); // add closing parenthesis
+      } else if (symbol is Power) {
+        stringBuilder.Append("POWER(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(",ROUND(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append(",0))");
+      } else if (symbol is Root) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")^(1 / ROUND(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append(",0))");
+      } else if (symbol is IfThenElse) {
+        stringBuilder.Append("IF(");
+        stringBuilder.Append("(" + FormatRecursively(node.GetSubtree(0)) + " ) > 0");
+        stringBuilder.Append(",");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append(",");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(2)));
+        stringBuilder.Append(")");
+      } else if (symbol is VariableCondition) {
+        VariableConditionTreeNode variableConditionTreeNode = node as VariableConditionTreeNode;
+        if (!variableConditionTreeNode.Symbol.IgnoreSlope) {
+          double threshold = variableConditionTreeNode.Threshold;
+          double slope = variableConditionTreeNode.Slope;
+          string p = "(1 / (1 + EXP(-" + slope.ToString(CultureInfo.InvariantCulture) + " * (" +
+                     GetColumnToVariableName(variableConditionTreeNode.VariableName) + "-" +
+                     threshold.ToString(CultureInfo.InvariantCulture) + "))))";
+          stringBuilder.Append("((");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+          stringBuilder.Append("*");
+          stringBuilder.Append(p);
+          stringBuilder.Append(") + (");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+          stringBuilder.Append("*(");
+          stringBuilder.Append("1 - " + p + ")");
+          stringBuilder.Append("))");
+        } else {
+          stringBuilder.AppendFormat(CultureInfo.InvariantCulture, "(IF({0} <= {1}, {2}, {3}))",
+            GetColumnToVariableName(variableConditionTreeNode.VariableName),
+            variableConditionTreeNode.Threshold,
+            FormatRecursively(node.GetSubtree(0)),
+            FormatRecursively(node.GetSubtree(1))
+            );
+        }
+      } else if (symbol is Xor) {
+        stringBuilder.Append("IF(");
+        stringBuilder.Append("XOR(");
+        stringBuilder.Append("(" + FormatRecursively(node.GetSubtree(0)) + ") > 0,");
+        stringBuilder.Append("(" + FormatRecursively(node.GetSubtree(1)) + ") > 0");
+        stringBuilder.Append("), 1.0, -1.0)");
+      } else if (symbol is Or) {
+        stringBuilder.Append("IF(");
+        stringBuilder.Append("OR(");
+        stringBuilder.Append("(" + FormatRecursively(node.GetSubtree(0)) + ") > 0,");
+        stringBuilder.Append("(" + FormatRecursively(node.GetSubtree(1)) + ") > 0");
+        stringBuilder.Append("), 1.0, -1.0)");
+      } else if (symbol is And) {
+        stringBuilder.Append("IF(");
+        stringBuilder.Append("AND(");
+        stringBuilder.Append("(" + FormatRecursively(node.GetSubtree(0)) + ") > 0,");
+        stringBuilder.Append("(" + FormatRecursively(node.GetSubtree(1)) + ") > 0");
+        stringBuilder.Append("), 1.0, -1.0)");
+      } else if (symbol is Not) {
+        stringBuilder.Append("IF(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" > 0, -1.0, 1.0)");
+      } else if (symbol is GreaterThan) {
+        stringBuilder.Append("IF((");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(") > (");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append("), 1.0, -1.0)");
+      } else if (symbol is LessThan) {
+        stringBuilder.Append("IF((");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(") < (");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append("), 1.0, -1.0)");
+      } else {
+        throw new NotImplementedException("Excel export of " + node.Symbol + " is not implemented.");
+      }
+      return stringBuilder.ToString();
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionLatexFormatter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionLatexFormatter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionLatexFormatter.cs	(revision 16337)
@@ -0,0 +1,512 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("LaTeX String Formatter", "Formatter for symbolic expression trees for import into LaTeX documents.")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionLatexFormatter : NamedItem, ISymbolicExpressionTreeStringFormatter {
+    private readonly List<KeyValuePair<string, double>> constants;
+    private int constIndex;
+    private int targetCount;
+    private int currentLag;
+    private string targetVariable;
+    private bool containsTimeSeriesSymbol;
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionLatexFormatter(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionLatexFormatter(SymbolicDataAnalysisExpressionLatexFormatter original, Cloner cloner)
+      : base(original, cloner) {
+      constants = new List<KeyValuePair<string, double>>(original.constants);
+      constIndex = original.constIndex;
+      currentLag = original.currentLag;
+      targetCount = original.targetCount;
+    }
+    public SymbolicDataAnalysisExpressionLatexFormatter()
+      : base() {
+      Name = ItemName;
+      Description = ItemDescription;
+      constants = new List<KeyValuePair<string, double>>();
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionLatexFormatter(this, cloner);
+    }
+
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree) {
+      return Format(symbolicExpressionTree, null);
+    }
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree, string targetVariable) {
+      try {
+        StringBuilder strBuilder = new StringBuilder();
+        constants.Clear();
+        constIndex = 0;
+        this.targetVariable = targetVariable;
+        containsTimeSeriesSymbol = symbolicExpressionTree.IterateNodesBreadth().Any(n => IsTimeSeriesSymbol(n.Symbol));
+        strBuilder.AppendLine(FormatRecursively(symbolicExpressionTree.Root));
+        return strBuilder.ToString();
+      } catch (NotImplementedException ex) {
+        return ex.Message + Environment.NewLine + ex.StackTrace;
+      }
+    }
+    static bool IsTimeSeriesSymbol(ISymbol s) {
+      return s is TimeLag || s is Integral || s is Derivative || s is LaggedVariable;
+    }
+
+    private string FormatRecursively(ISymbolicExpressionTreeNode node) {
+      StringBuilder strBuilder = new StringBuilder();
+      currentLag = 0;
+      FormatBegin(node, strBuilder);
+
+      if (node.SubtreeCount > 0) {
+        strBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+      }
+      int i = 1;
+      foreach (var subTree in node.Subtrees.Skip(1)) {
+        FormatSep(node, strBuilder, i);
+        // format the whole subtree
+        strBuilder.Append(FormatRecursively(subTree));
+        i++;
+      }
+
+      FormatEnd(node, strBuilder);
+
+      return strBuilder.ToString();
+    }
+
+    private void FormatBegin(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.Symbol is Addition) {
+        strBuilder.Append(@" \left( ");
+      } else if (node.Symbol is Subtraction) {
+        if (node.SubtreeCount == 1) {
+          strBuilder.Append(@"- \left( ");
+        } else {
+          strBuilder.Append(@" \left( ");
+        }
+      } else if (node.Symbol is Multiplication) {
+      } else if (node.Symbol is Division) {
+        if (node.SubtreeCount == 1) {
+          strBuilder.Append(@" \cfrac{1}{");
+        } else {
+          strBuilder.Append(@" \cfrac{ ");
+        }
+      } else if (node.Symbol is Average) {
+        // skip output of (1/1) if only one subtree
+        if (node.SubtreeCount > 1) {
+          strBuilder.Append(@" \cfrac{1}{" + node.SubtreeCount + @"}");
+        }
+        strBuilder.Append(@" \left( ");
+      } else if (node.Symbol is Logarithm) {
+        strBuilder.Append(@"\log \left( ");
+      } else if (node.Symbol is Exponential) {
+        strBuilder.Append(@"\exp \left( ");
+      } else if (node.Symbol is Square) {
+        strBuilder.Append(@"\left(");
+      } else if (node.Symbol is SquareRoot) {
+        strBuilder.Append(@"\sqrt{");
+      } else if (node.Symbol is Sine) {
+        strBuilder.Append(@"\sin \left( ");
+      } else if (node.Symbol is Cosine) {
+        strBuilder.Append(@"\cos \left( ");
+      } else if (node.Symbol is Tangent) {
+        strBuilder.Append(@"\tan \left( ");
+      } else if (node.Symbol is AiryA) {
+        strBuilder.Append(@"\operatorname{airy}_a \left( ");
+      } else if (node.Symbol is AiryB) {
+        strBuilder.Append(@"\operatorname{airy}_b \left( ");
+      } else if (node.Symbol is Bessel) {
+        strBuilder.Append(@"\operatorname{bessel}_1 \left( ");
+      } else if (node.Symbol is CosineIntegral) {
+        strBuilder.Append(@"\operatorname{cosInt} \left( ");
+      } else if (node.Symbol is Dawson) {
+        strBuilder.Append(@"\operatorname{dawson} \left( ");
+      } else if (node.Symbol is Erf) {
+        strBuilder.Append(@"\operatorname{erf} \left( ");
+      } else if (node.Symbol is ExponentialIntegralEi) {
+        strBuilder.Append(@"\operatorname{expInt}_i \left( ");
+      } else if (node.Symbol is FresnelCosineIntegral) {
+        strBuilder.Append(@"\operatorname{fresnel}_\operatorname{cosInt} \left( ");
+      } else if (node.Symbol is FresnelSineIntegral) {
+        strBuilder.Append(@"\operatorname{fresnel}_\operatorname{sinInt} \left( ");
+      } else if (node.Symbol is Gamma) {
+        strBuilder.Append(@"\Gamma \left( ");
+      } else if (node.Symbol is HyperbolicCosineIntegral) {
+        strBuilder.Append(@"\operatorname{hypCosInt} \left( ");
+      } else if (node.Symbol is HyperbolicSineIntegral) {
+        strBuilder.Append(@"\operatorname{hypSinInt} \left( ");
+      } else if (node.Symbol is Norm) {
+        strBuilder.Append(@"\operatorname{norm} \left( ");
+      } else if (node.Symbol is Psi) {
+        strBuilder.Append(@"\operatorname{digamma} \left( ");
+      } else if (node.Symbol is SineIntegral) {
+        strBuilder.Append(@"\operatorname{sinInt} \left( ");
+      } else if (node.Symbol is GreaterThan) {
+        strBuilder.Append(@"  \left( ");
+      } else if (node.Symbol is LessThan) {
+        strBuilder.Append(@"  \left( ");
+      } else if (node.Symbol is And) {
+        strBuilder.Append(@"  \left( \left( ");
+      } else if (node.Symbol is Or) {
+        strBuilder.Append(@"   \left( \left( ");
+      } else if (node.Symbol is Not) {
+        strBuilder.Append(@" \neg \left( ");
+      } else if (node.Symbol is IfThenElse) {
+        strBuilder.Append(@" \operatorname{if}  \left( ");
+      } else if (node.Symbol is Constant) {
+        var constName = "c_{" + constIndex + "}";
+        constIndex++;
+        var constNode = node as ConstantTreeNode;
+        if (constNode.Value.IsAlmost(1.0)) {
+          strBuilder.Append("1 ");
+        } else {
+          strBuilder.Append(constName);
+          constants.Add(new KeyValuePair<string, double>(constName, constNode.Value));
+        }
+
+      } else if (node.Symbol is FactorVariable) {
+        var factorNode = node as FactorVariableTreeNode;
+        var constName = "c_{" + constIndex + "}";
+        strBuilder.Append(constName + " ");
+        foreach (var e in factorNode.Symbol.GetVariableValues(factorNode.VariableName)
+          .Zip(factorNode.Weights, Tuple.Create)) {
+          constants.Add(new KeyValuePair<string, double>("c_{" + constIndex + ", " + EscapeLatexString(factorNode.VariableName) + "=" + EscapeLatexString(e.Item1) + "}", e.Item2));
+        }
+        constIndex++;
+      } else if (node.Symbol is BinaryFactorVariable) {
+        var binFactorNode = node as BinaryFactorVariableTreeNode;
+        if (!binFactorNode.Weight.IsAlmost((1.0))) {
+          var constName = "c_{" + constIndex + "}";
+          strBuilder.Append(constName + "  \\cdot");
+          constants.Add(new KeyValuePair<string, double>(constName, binFactorNode.Weight));
+          constIndex++;
+        }
+        strBuilder.Append("(" + EscapeLatexString(binFactorNode.VariableName));
+        strBuilder.Append(LagToString(currentLag));
+        strBuilder.Append(" = " + EscapeLatexString(binFactorNode.VariableValue) + " )");
+      } else if (node.Symbol is LaggedVariable) {
+        var laggedVarNode = node as LaggedVariableTreeNode;
+        if (!laggedVarNode.Weight.IsAlmost(1.0)) {
+          var constName = "c_{" + constIndex + "}";
+          strBuilder.Append(constName + "  \\cdot");
+          constants.Add(new KeyValuePair<string, double>(constName, laggedVarNode.Weight));
+          constIndex++;
+        }
+        strBuilder.Append(EscapeLatexString(laggedVarNode.VariableName));
+        strBuilder.Append(LagToString(currentLag + laggedVarNode.Lag));
+
+      } else if (node.Symbol is Variable) {
+        var varNode = node as VariableTreeNode;
+        if (!varNode.Weight.IsAlmost((1.0))) {
+          var constName = "c_{" + constIndex + "}";
+          strBuilder.Append(constName + "  \\cdot");
+          constants.Add(new KeyValuePair<string, double>(constName, varNode.Weight));
+          constIndex++;
+        }
+        strBuilder.Append(EscapeLatexString(varNode.VariableName));
+        strBuilder.Append(LagToString(currentLag));
+      } else if (node.Symbol is ProgramRootSymbol) {
+        strBuilder
+          .AppendLine("\\begin{align*}")
+          .AppendLine("\\nonumber");
+      } else if (node.Symbol is Defun) {
+        var defunNode = node as DefunTreeNode;
+        strBuilder.Append(defunNode.FunctionName + " & = ");
+      } else if (node.Symbol is InvokeFunction) {
+        var invokeNode = node as InvokeFunctionTreeNode;
+        strBuilder.Append(invokeNode.Symbol.FunctionName + @" \left( ");
+      } else if (node.Symbol is StartSymbol) {
+        FormatStartSymbol(strBuilder);
+      } else if (node.Symbol is Argument) {
+        var argSym = node.Symbol as Argument;
+        strBuilder.Append(" ARG+" + argSym.ArgumentIndex + " ");
+      } else if (node.Symbol is Derivative) {
+        strBuilder.Append(@" \cfrac{d \left( ");
+      } else if (node.Symbol is TimeLag) {
+        var laggedNode = node as ILaggedTreeNode;
+        currentLag += laggedNode.Lag;
+      } else if (node.Symbol is Power) {
+        strBuilder.Append(@" \left( ");
+      } else if (node.Symbol is Root) {
+        strBuilder.Append(@" \left( ");
+      } else if (node.Symbol is Integral) {
+        // actually a new variable for t is needed in all subtrees (TODO)
+        var laggedTreeNode = node as ILaggedTreeNode;
+        strBuilder.Append(@"\sum_{t=" + (laggedTreeNode.Lag + currentLag) + @"}^0 \left( ");
+      } else if (node.Symbol is VariableCondition) {
+        var conditionTreeNode = node as VariableConditionTreeNode;
+        var constName = "c_{" + constants.Count + "}";
+        string p = @"1 /  1 + \exp  - " + constName + " ";
+        constants.Add(new KeyValuePair<string, double>(constName, conditionTreeNode.Slope));
+        constIndex++;
+        var const2Name = "c_{" + constants.Count + @"}";
+        p += @" \cdot " + EscapeLatexString(conditionTreeNode.VariableName) + LagToString(currentLag) + " - " + const2Name + "   ";
+        constants.Add(new KeyValuePair<string, double>(const2Name, conditionTreeNode.Threshold));
+        constIndex++;
+        strBuilder.Append(@" \left( " + p + @"\cdot ");
+      } else {
+        throw new NotImplementedException("Export of " + node.Symbol + " is not implemented.");
+      }
+    }
+
+    private void FormatSep(ISymbolicExpressionTreeNode node, StringBuilder strBuilder, int step) {
+      if (node.Symbol is Addition) {
+        strBuilder.Append(" + ");
+      } else if (node.Symbol is Subtraction) {
+        strBuilder.Append(" - ");
+      } else if (node.Symbol is Multiplication) {
+        strBuilder.Append(@" \cdot ");
+      } else if (node.Symbol is Division) {
+        if (step + 1 == node.SubtreeCount)
+          strBuilder.Append(@"}{");
+        else
+          strBuilder.Append(@" }{ \cfrac{ ");
+      } else if (node.Symbol is Average) {
+        strBuilder.Append(@" + ");
+      } else if (node.Symbol is Logarithm) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Exponential) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Square) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is SquareRoot) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Sine) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Cosine) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Tangent) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is AiryA) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is AiryB) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Bessel) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is CosineIntegral) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Dawson) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Erf) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is ExponentialIntegralEi) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is FresnelCosineIntegral) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is FresnelSineIntegral) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Gamma) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is HyperbolicCosineIntegral) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is HyperbolicSineIntegral) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Norm) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is Psi) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is SineIntegral) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is GreaterThan) {
+        strBuilder.Append(@" > ");
+      } else if (node.Symbol is LessThan) {
+        strBuilder.Append(@" < ");
+      } else if (node.Symbol is And) {
+        strBuilder.Append(@" > 0  \right) \land \left(");
+      } else if (node.Symbol is Or) {
+        strBuilder.Append(@" > 0  \right) \lor \left(");
+      } else if (node.Symbol is Not) {
+        throw new InvalidOperationException();
+      } else if (node.Symbol is IfThenElse) {
+        strBuilder.Append(@" , ");
+      } else if (node.Symbol is ProgramRootSymbol) {
+        strBuilder.Append(@"\\" + Environment.NewLine);
+      } else if (node.Symbol is Defun) {
+      } else if (node.Symbol is InvokeFunction) {
+        strBuilder.Append(" , ");
+      } else if (node.Symbol is StartSymbol) {
+        strBuilder.Append(@"\\" + Environment.NewLine);
+        FormatStartSymbol(strBuilder);
+      } else if (node.Symbol is Power) {
+        strBuilder.Append(@"\right) ^ { \operatorname{round} \left(");
+      } else if (node.Symbol is Root) {
+        strBuilder.Append(@"\right) ^ {  \cfrac{1}{ \operatorname{round} \left(");
+      } else if (node.Symbol is VariableCondition) {
+        var conditionTreeNode = node as VariableConditionTreeNode;
+        var const1Name = "c_{" + constants.Count + "}";
+        string p = @"1 / \left( 1 + \exp \left( - " + const1Name + " ";
+        constants.Add(new KeyValuePair<string, double>(const1Name, conditionTreeNode.Slope));
+        constIndex++;
+        var const2Name = "c_{" + constants.Count + "}";
+        p += @" \cdot " + EscapeLatexString(conditionTreeNode.VariableName) + LagToString(currentLag) + " - " + const2Name + " \right) \right) \right)   ";
+        constants.Add(new KeyValuePair<string, double>(const2Name, conditionTreeNode.Threshold));
+        constIndex++;
+        strBuilder.Append(@" +  \left( 1 - " + p + @" \right) \cdot ");
+      } else {
+        throw new NotImplementedException("Export of " + node.Symbol + " is not implemented.");
+      }
+    }
+
+    private void FormatEnd(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.Symbol is Addition) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Subtraction) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Multiplication) {
+      } else if (node.Symbol is Division) {
+        strBuilder.Append(" } ");
+        for (int i = 2; i < node.SubtreeCount; i++)
+          strBuilder.Append(" } ");
+      } else if (node.Symbol is Average) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Logarithm) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Exponential) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Square) {
+        strBuilder.Append(@"\right)^2");
+      } else if (node.Symbol is SquareRoot) {
+        strBuilder.Append(@"}");
+      } else if (node.Symbol is Sine) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Cosine) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Tangent) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is AiryA) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is AiryB) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Bessel) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is CosineIntegral) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Dawson) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Erf) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is ExponentialIntegralEi) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is FresnelCosineIntegral) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is FresnelSineIntegral) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Gamma) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is HyperbolicCosineIntegral) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is HyperbolicSineIntegral) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Norm) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Psi) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is SineIntegral) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is GreaterThan) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is LessThan) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is And) {
+        strBuilder.Append(@" > 0 \right) \right) ");
+      } else if (node.Symbol is Or) {
+        strBuilder.Append(@" > 0 \right) \right) ");
+      } else if (node.Symbol is Not) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is IfThenElse) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is Constant) {
+      } else if (node.Symbol is LaggedVariable) {
+      } else if (node.Symbol is Variable) {
+      } else if (node.Symbol is FactorVariable) {
+      } else if (node.Symbol is BinaryFactorVariable) {
+      } else if (node.Symbol is ProgramRootSymbol) {
+        strBuilder
+          .AppendLine("\\end{align*}")
+          .AppendLine("\\begin{align*}")
+          .AppendLine("\\nonumber");
+        // output all constant values
+        if (constants.Count > 0) {
+          foreach (var constant in constants) {
+            // replace "." with ".&" to align decimal points
+            var constStr = string.Format(System.Globalization.NumberFormatInfo.InvariantInfo, "{0:G5}", constant.Value);
+            if (!constStr.Contains(".")) constStr = constStr + ".0";
+            constStr = constStr.Replace(".", "&.");  // fix problem in rendering of aligned expressions
+            strBuilder.Append(constant.Key + "& = & " + constStr);
+            strBuilder.Append(@"\\");
+          }
+        }
+        strBuilder.AppendLine("\\end{align*}");
+      } else if (node.Symbol is Defun) {
+      } else if (node.Symbol is InvokeFunction) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is StartSymbol) {
+      } else if (node.Symbol is Argument) {
+      } else if (node.Symbol is Derivative) {
+        strBuilder.Append(@" \right) }{dt} ");
+      } else if (node.Symbol is TimeLag) {
+        var laggedNode = node as ILaggedTreeNode;
+        currentLag -= laggedNode.Lag;
+      } else if (node.Symbol is Power) {
+        strBuilder.Append(@" \right) } ");
+      } else if (node.Symbol is Root) {
+        strBuilder.Append(@" \right) } } ");
+      } else if (node.Symbol is Integral) {
+        strBuilder.Append(@" \right) ");
+      } else if (node.Symbol is VariableCondition) {
+        strBuilder.Append(@"\right) ");
+      } else {
+        throw new NotImplementedException("Export of " + node.Symbol + " is not implemented.");
+      }
+    }
+
+    private void FormatStartSymbol(StringBuilder strBuilder) {
+      strBuilder.Append(targetVariable ?? "target_" + (targetCount++));
+      if (containsTimeSeriesSymbol)
+        strBuilder.Append("(t)");
+      strBuilder.Append(" & = ");
+    }
+
+    private string LagToString(int lag) {
+      if (lag < 0) {
+        return "(t" + lag + ")";
+      } else if (lag > 0) {
+        return "(t+" + lag + ")";
+      } else return "";
+    }
+
+    private string EscapeLatexString(string s) {
+      return "\\text{" +
+        s
+         .Replace("\\", "\\\\")
+         .Replace("{", "\\{")
+         .Replace("}", "\\}")
+        + "}";
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionMATLABFormatter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionMATLABFormatter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionMATLABFormatter.cs	(revision 16337)
@@ -0,0 +1,390 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+
+  [Item("MATLAB String Formatter", "String formatter for string representations of symbolic data analysis expressions in MATLAB syntax.")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionMATLABFormatter : NamedItem, ISymbolicExpressionTreeStringFormatter {
+    private int currentLag;
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionMATLABFormatter(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionMATLABFormatter(SymbolicDataAnalysisExpressionMATLABFormatter original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisExpressionMATLABFormatter()
+      : base() {
+      Name = ItemName;
+      Description = ItemDescription;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionMATLABFormatter(this, cloner);
+    }
+    private int currentIndexNumber;
+    public string CurrentIndexVariable {
+      get {
+        return "i" + currentIndexNumber;
+      }
+    }
+    private void ReleaseIndexVariable() {
+      currentIndexNumber--;
+    }
+
+    private string AllocateIndexVariable() {
+      currentIndexNumber++;
+      return CurrentIndexVariable;
+    }
+
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree) {
+      currentLag = 0;
+      currentIndexNumber = 0;
+
+      var stringBuilder = new StringBuilder();
+      stringBuilder.AppendLine("rows = ???");
+      stringBuilder.AppendLine(FormatOnlyExpression(symbolicExpressionTree.Root) + ";");
+      stringBuilder.AppendLine();
+      stringBuilder.AppendLine("function y = log_(x)");
+      stringBuilder.AppendLine("  if(x<=0) y = NaN;");
+      stringBuilder.AppendLine("  else     y = log(x);");
+      stringBuilder.AppendLine("  end");
+      stringBuilder.AppendLine("end");
+      stringBuilder.AppendLine();
+      stringBuilder.AppendLine("function y = fivePoint(f0, f1, f3, f4)");
+      stringBuilder.AppendLine("  y = (f0 + 2*f1 - 2*f3 - f4) / 8;");
+      stringBuilder.AppendLine("end");
+
+      var factorVariableNames =
+        symbolicExpressionTree.IterateNodesPostfix()
+          .OfType<FactorVariableTreeNode>()
+          .Select(n => n.VariableName)
+          .Distinct();
+
+      foreach (var factorVarName in factorVariableNames) {
+        var factorSymb = symbolicExpressionTree.IterateNodesPostfix()
+          .OfType<FactorVariableTreeNode>()
+          .First(n => n.VariableName == factorVarName)
+          .Symbol;
+        stringBuilder.AppendFormat("function y = switch_{0}(val, v)", factorVarName).AppendLine();
+        var values = factorSymb.GetVariableValues(factorVarName).ToArray();
+        stringBuilder.AppendLine("switch val");
+        for (int i = 0; i < values.Length; i++) {
+          stringBuilder.AppendFormat(CultureInfo.InvariantCulture, "  case \"{0}\" y = v({1})", values[i], i).AppendLine();
+        }
+        stringBuilder.AppendLine("end");
+        stringBuilder.AppendLine();
+      }
+
+      return stringBuilder.ToString();
+    }
+
+    public string FormatOnlyExpression(ISymbolicExpressionTreeNode expressionNode) {
+      var stringBuilder = new StringBuilder();
+      stringBuilder.AppendLine("  for " + CurrentIndexVariable + " = 1:1:rows");
+      stringBuilder.AppendLine("    estimated(" + CurrentIndexVariable + ") = " + FormatRecursively(expressionNode.GetSubtree(0)) + ";");
+      stringBuilder.AppendLine("  end;");
+      return stringBuilder.ToString();
+    }
+
+    private string FormatRecursively(ISymbolicExpressionTreeNode node) {
+      ISymbol symbol = node.Symbol;
+      StringBuilder stringBuilder = new StringBuilder();
+
+      if (symbol is ProgramRootSymbol) {
+        stringBuilder.AppendLine(FormatRecursively(node.GetSubtree(0)));
+      } else if (symbol is StartSymbol)
+        return FormatRecursively(node.GetSubtree(0));
+      else if (symbol is Addition) {
+        stringBuilder.Append("(");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("+");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+        }
+        stringBuilder.Append(")");
+      } else if (symbol is And) {
+        stringBuilder.Append("((");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("&");
+          stringBuilder.Append("((");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          stringBuilder.Append(")>0)");
+        }
+        stringBuilder.Append(")-0.5)*2");
+        // MATLAB maps false and true to 0 and 1, resp., we map this result to -1.0 and +1.0, resp.
+      } else if (symbol is Average) {
+        stringBuilder.Append("(1/");
+        stringBuilder.Append(node.SubtreeCount);
+        stringBuilder.Append(")*(");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("+");
+          stringBuilder.Append("(");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          stringBuilder.Append(")");
+        }
+        stringBuilder.Append(")");
+      } else if (symbol is Constant) {
+        ConstantTreeNode constantTreeNode = node as ConstantTreeNode;
+        stringBuilder.Append(constantTreeNode.Value.ToString(CultureInfo.InvariantCulture));
+      } else if (symbol is Cosine) {
+        stringBuilder.Append("cos(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Division) {
+        if (node.SubtreeCount == 1) {
+          stringBuilder.Append("1/");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        } else {
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+          stringBuilder.Append("/(");
+          for (int i = 1; i < node.SubtreeCount; i++) {
+            if (i > 1) stringBuilder.Append("*");
+            stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          }
+          stringBuilder.Append(")");
+        }
+      } else if (symbol is Exponential) {
+        stringBuilder.Append("exp(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Square) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(").^2");
+      } else if (symbol is SquareRoot) {
+        stringBuilder.Append("sqrt(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is GreaterThan) {
+        stringBuilder.Append("((");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(">");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append(")-0.5)*2");
+        // MATLAB maps false and true to 0 and 1, resp., we map this result to -1.0 and +1.0, resp.
+      } else if (symbol is IfThenElse) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(">0)*");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append("+");
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append("<=0)*");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(2)));
+      } else if (symbol is LaggedVariable) {
+        // this if must be checked before if(symbol is LaggedVariable)
+        LaggedVariableTreeNode laggedVariableTreeNode = node as LaggedVariableTreeNode;
+        stringBuilder.Append(laggedVariableTreeNode.Weight.ToString(CultureInfo.InvariantCulture));
+        stringBuilder.Append("*");
+        stringBuilder.Append(laggedVariableTreeNode.VariableName +
+                             LagToString(currentLag + laggedVariableTreeNode.Lag));
+      } else if (symbol is LessThan) {
+        stringBuilder.Append("((");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append("<");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append(")-0.5)*2");
+        // MATLAB maps false and true to 0 and 1, resp., we map this result to -1.0 and +1.0, resp.
+      } else if (symbol is Logarithm) {
+        stringBuilder.Append("log_(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Multiplication) {
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("*");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+        }
+      } else if (symbol is Not) {
+        stringBuilder.Append("~(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" > 0 )");
+      } else if (symbol is Or) {
+        stringBuilder.Append("((");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("|");
+          stringBuilder.Append("((");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          stringBuilder.Append(")>0)");
+        }
+        stringBuilder.Append(")-0.5)*2");
+        // MATLAB maps false and true to 0 and 1, resp., we map this result to -1.0 and +1.0, resp.
+      } else if (symbol is Sine) {
+        stringBuilder.Append("sin(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is Subtraction) {
+        stringBuilder.Append("(");
+        if (node.SubtreeCount == 1) {
+          stringBuilder.Append("-");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        } else {
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+          for (int i = 1; i < node.SubtreeCount; i++) {
+            stringBuilder.Append("-");
+            stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          }
+        }
+        stringBuilder.Append(")");
+      } else if (symbol is Tangent) {
+        stringBuilder.Append("tan(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is AiryA) {
+        stringBuilder.Append("airy(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is AiryB) {
+        stringBuilder.Append("airy(2, ");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is Bessel) {
+        stringBuilder.Append("besseli(0.0,");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is CosineIntegral) {
+        stringBuilder.Append("cosint(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is Dawson) {
+        stringBuilder.Append("dawson(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is Erf) {
+        stringBuilder.Append("erf(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is ExponentialIntegralEi) {
+        stringBuilder.Append("expint(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is FresnelCosineIntegral) {
+        stringBuilder.Append("FresnelC(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is FresnelSineIntegral) {
+        stringBuilder.Append("FresnelS(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is Gamma) {
+        stringBuilder.Append("gamma(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is HyperbolicCosineIntegral) {
+        stringBuilder.Append("Chi(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is HyperbolicSineIntegral) {
+        stringBuilder.Append("Shi(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is Norm) {
+        stringBuilder.Append("normpdf(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is Psi) {
+        stringBuilder.Append("psi(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (node.Symbol is SineIntegral) {
+        stringBuilder.Append("sinint(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+      } else if (symbol is HeuristicLab.Problems.DataAnalysis.Symbolic.Variable) {
+        VariableTreeNode variableTreeNode = node as VariableTreeNode;
+        stringBuilder.Append(variableTreeNode.Weight.ToString(CultureInfo.InvariantCulture));
+        stringBuilder.Append("*");
+        stringBuilder.Append(variableTreeNode.VariableName + LagToString(currentLag));
+      } else if (symbol is HeuristicLab.Problems.DataAnalysis.Symbolic.FactorVariable) {
+        var factorNode = node as FactorVariableTreeNode;
+        var weights = string.Join(" ", factorNode.Weights.Select(w => w.ToString("G17", CultureInfo.InvariantCulture)));
+        stringBuilder.AppendFormat("switch_{0}(\"{1}\",[{2}])",
+          factorNode.VariableName, factorNode.VariableName, weights)
+          .AppendLine();
+      } else if (symbol is HeuristicLab.Problems.DataAnalysis.Symbolic.BinaryFactorVariable) {
+        var factorNode = node as BinaryFactorVariableTreeNode;
+        stringBuilder.AppendFormat(CultureInfo.InvariantCulture,
+          "((strcmp({0},\"{1}\")==1) * {2:G17})", factorNode.VariableName, factorNode.VariableValue, factorNode.Weight);
+      } else if (symbol is Power) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")^round(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append(")");
+      } else if (symbol is Root) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")^(1 / round(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append("))");
+      } else if (symbol is Derivative) {
+        stringBuilder.Append("fivePoint(");
+        // f0
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(", ");
+        // f1
+        currentLag--;
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(", ");
+        // f3
+        currentLag -= 2;
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(", ");
+        currentLag--;
+        // f4
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(")");
+        currentLag += 4;
+      } else if (symbol is Integral) {
+        var laggedNode = node as LaggedTreeNode;
+        string prevCounterVariable = CurrentIndexVariable;
+        string counterVariable = AllocateIndexVariable();
+        stringBuilder.AppendLine(" sum (map(@(" + counterVariable + ") " + FormatRecursively(node.GetSubtree(0)) +
+                                 ", (" + prevCounterVariable + "+" + laggedNode.Lag + "):" + prevCounterVariable +
+                                 "))");
+        ReleaseIndexVariable();
+      } else if (symbol is TimeLag) {
+        var laggedNode = node as LaggedTreeNode;
+        currentLag += laggedNode.Lag;
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        currentLag -= laggedNode.Lag;
+      } else {
+        stringBuilder.Append("ERROR");
+      }
+      return stringBuilder.ToString();
+    }
+
+
+    private string LagToString(int lag) {
+      if (lag < 0) {
+        return "(" + CurrentIndexVariable + "" + lag + ")";
+      } else if (lag > 0) {
+        return "(" + CurrentIndexVariable + "+" + lag + ")";
+      } else return "(" + CurrentIndexVariable + ")";
+    }
+
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionMathematicaFormatter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionMathematicaFormatter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionMathematicaFormatter.cs	(revision 16337)
@@ -0,0 +1,246 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("Mathematica Symbolic Expression Tree Formatter", "A string formatter that converts symbolic expression trees to Mathematica expressions.")]
+  [StorableClass]
+  public sealed class SymbolicDataAnalysisExpressionMathematicaFormatter : NamedItem, ISymbolicExpressionTreeStringFormatter {
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionMathematicaFormatter(bool deserializing) : base(deserializing) { }
+    private SymbolicDataAnalysisExpressionMathematicaFormatter(SymbolicDataAnalysisExpressionMathematicaFormatter original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisExpressionMathematicaFormatter()
+      : base() {
+      Name = ItemName;
+      Description = ItemDescription;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionMathematicaFormatter(this, cloner);
+    }
+
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree) {
+      // skip root and start symbols
+      StringBuilder strBuilder = new StringBuilder();
+      FormatRecursively(symbolicExpressionTree.Root.GetSubtree(0).GetSubtree(0), strBuilder);
+      return strBuilder.ToString();
+    }
+
+    private void FormatRecursively(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.Subtrees.Any()) {
+        if (node.Symbol is Addition) {
+          FormatFunction(node, "Plus", strBuilder);
+        } else if (node.Symbol is Average) {
+          FormatAverage(node, strBuilder);
+        } else if (node.Symbol is Multiplication) {
+          FormatFunction(node, "Times", strBuilder);
+        } else if (node.Symbol is Subtraction) {
+          FormatSubtraction(node, strBuilder);
+        } else if (node.Symbol is Division) {
+          FormatDivision(node, strBuilder);
+        } else if (node.Symbol is Sine) {
+          FormatFunction(node, "Sin", strBuilder);
+        } else if (node.Symbol is Cosine) {
+          FormatFunction(node, "Cos", strBuilder);
+        } else if (node.Symbol is Tangent) {
+          FormatFunction(node, "Tan", strBuilder);
+        } else if (node.Symbol is Exponential) {
+          FormatFunction(node, "Exp", strBuilder);
+        } else if (node.Symbol is Logarithm) {
+          FormatFunction(node, "Log", strBuilder);
+        } else if (node.Symbol is IfThenElse) {
+          FormatIf(node, strBuilder);
+        } else if (node.Symbol is GreaterThan) {
+          strBuilder.Append("If[Greater[");
+          FormatRecursively(node.GetSubtree(0), strBuilder);
+          strBuilder.Append(",");
+          FormatRecursively(node.GetSubtree(1), strBuilder);
+          strBuilder.Append("], 1, -1]");
+        } else if (node.Symbol is LessThan) {
+          strBuilder.Append("If[Less[");
+          FormatRecursively(node.GetSubtree(0), strBuilder);
+          strBuilder.Append(",");
+          FormatRecursively(node.GetSubtree(1), strBuilder);
+          strBuilder.Append("], 1, -1]");
+        } else if (node.Symbol is And) {
+          FormatAnd(node, strBuilder);
+        } else if (node.Symbol is Not) {
+          strBuilder.Append("If[Greater[");
+          FormatRecursively(node.GetSubtree(0), strBuilder);
+          strBuilder.Append(", 0], -1, 1]");
+        } else if (node.Symbol is Or) {
+          FormatOr(node, strBuilder);
+        } else if (node.Symbol is Xor) {
+          FormatXor(node, strBuilder);
+        } else if (node.Symbol is Square) {
+          FormatSquare(node, strBuilder);
+        } else if (node.Symbol is SquareRoot) {
+          FormatFunction(node, "Sqrt", strBuilder);
+        } else if (node.Symbol is Power) {
+          FormatFunction(node, "Power", strBuilder);
+        } else if (node.Symbol is Root) {
+          FormatRoot(node, strBuilder);
+        } else {
+          throw new NotSupportedException("Formatting of symbol: " + node.Symbol + " is not supported.");
+        }
+      } else {
+        // terminals
+        if (node.Symbol is Variable) {
+          var varNode = node as VariableTreeNode;
+          strBuilder.AppendFormat("Times[{0}, {1}]", varNode.VariableName, varNode.Weight.ToString("G17", CultureInfo.InvariantCulture));
+        } else if (node.Symbol is Constant) {
+          var constNode = node as ConstantTreeNode;
+          strBuilder.Append(constNode.Value.ToString("G17", CultureInfo.InvariantCulture));
+        } else if (node.Symbol is FactorVariable) {
+          var factorNode = node as FactorVariableTreeNode;
+          strBuilder.AppendFormat("Switch[{0},", factorNode.VariableName);
+          var varValues = factorNode.Symbol.GetVariableValues(factorNode.VariableName).ToArray();
+          var weights = varValues.Select(factorNode.GetValue).ToArray();
+
+          var weightStr = string.Join(", ",
+            varValues.Zip(weights, (s, d) => string.Format(CultureInfo.InvariantCulture, "\"{0}\", {1:G17}", s, d)));
+          strBuilder.Append(weightStr);
+          strBuilder.Append("]");
+        } else if (node.Symbol is BinaryFactorVariable) {
+          var factorNode = node as BinaryFactorVariableTreeNode;
+          strBuilder.AppendFormat(CultureInfo.InvariantCulture, "If[{0}==\"{1}\",{2:G17},0.0]",
+            factorNode.VariableName, factorNode.VariableValue, factorNode.Weight);
+        } else {
+          throw new NotSupportedException("Formatting of symbol: " + node.Symbol + " is not supported.");
+        }
+      }
+    }
+
+    private void FormatXor(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("If[Xor[");
+      foreach (var t in node.Subtrees) {
+        strBuilder.Append("Greater[");
+        FormatRecursively(t, strBuilder);
+        strBuilder.Append(", 0]");
+        if (t != node.Subtrees.Last()) strBuilder.Append(",");
+      }
+      strBuilder.Append("], 1, -1]");
+    }
+
+    private void FormatOr(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("If[Or[");
+      foreach (var t in node.Subtrees) {
+        strBuilder.Append("Greater[");
+        FormatRecursively(t, strBuilder);
+        strBuilder.Append(", 0]");
+        if (t != node.Subtrees.Last()) strBuilder.Append(",");
+      }
+      strBuilder.Append("], 1, -1]");
+    }
+
+    private void FormatAnd(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("If[And[");
+      foreach (var t in node.Subtrees) {
+        strBuilder.Append("Greater[");
+        FormatRecursively(t, strBuilder);
+        strBuilder.Append(", 0]");
+        if (t != node.Subtrees.Last()) strBuilder.Append(",");
+      }
+      strBuilder.Append("], 1, -1]");
+    }
+
+    private void FormatIf(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("If[Greater[");
+      FormatRecursively(node.GetSubtree(0), strBuilder);
+      strBuilder.Append(", 0], ");
+      FormatRecursively(node.GetSubtree(1), strBuilder);
+      strBuilder.Append(", ");
+      FormatRecursively(node.GetSubtree(2), strBuilder);
+      strBuilder.Append("]");
+    }
+
+    private void FormatAverage(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      // mean function needs a list of values
+      strBuilder.Append("Mean[{");
+      FormatRecursively(node.GetSubtree(0), strBuilder);
+      for (int i = 1; i < node.SubtreeCount; i++) {
+        strBuilder.Append(",");
+        FormatRecursively(node.GetSubtree(i), strBuilder);
+      }
+      strBuilder.Append("}]");
+    }
+
+    private void FormatSubtraction(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("Subtract[");
+      FormatRecursively(node.GetSubtree(0), strBuilder);
+      strBuilder.Append(", Times[-1");
+      foreach (var t in node.Subtrees) {
+        strBuilder.Append(",");
+        FormatRecursively(t, strBuilder);
+      }
+      strBuilder.Append("]]");
+    }
+
+    private void FormatSquare(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("Power[");
+      FormatRecursively(node.GetSubtree(0), strBuilder);
+      strBuilder.Append(", 2]");
+    }
+
+    private void FormatRoot(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("Power[");
+      FormatRecursively(node.GetSubtree(0), strBuilder);
+      strBuilder.Append(", Divide[1,");
+      FormatRecursively(node.GetSubtree(1), strBuilder);
+      strBuilder.Append("]]");
+    }
+
+    private void FormatDivision(ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.SubtreeCount == 1) {
+        strBuilder.Append("Divide[1, ");
+        FormatRecursively(node.GetSubtree(0), strBuilder);
+        strBuilder.Append("]");
+      } else {
+        strBuilder.Append("Divide[");
+        FormatRecursively(node.GetSubtree(0), strBuilder);
+        strBuilder.Append(", Times[");
+        FormatRecursively(node.GetSubtree(1), strBuilder);
+        for (int i = 2; i < node.SubtreeCount; i++) {
+          strBuilder.Append(",");
+          FormatRecursively(node.GetSubtree(i), strBuilder);
+        }
+        strBuilder.Append("]]");
+      }
+    }
+
+    private void FormatFunction(ISymbolicExpressionTreeNode node, string function, StringBuilder strBuilder) {
+      strBuilder.Append(function + "[");
+      foreach (var child in node.Subtrees) {
+        FormatRecursively(child, strBuilder);
+        if (child != node.Subtrees.Last())
+          strBuilder.Append(", ");
+      }
+      strBuilder.Append("]");
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionSmalltalkFormatter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionSmalltalkFormatter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/SymbolicDataAnalysisExpressionSmalltalkFormatter.cs	(revision 16337)
@@ -0,0 +1,187 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Globalization;
+using System.Text;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+
+  [Item("Smalltalk String Formatter", "String formatter for string representations of symbolic expression trees in Smalltalk syntax.")]
+  public class SymbolicDataAnalysisExpressionSmalltalkFormatter : NamedItem, ISymbolicExpressionTreeStringFormatter {
+
+    protected SymbolicDataAnalysisExpressionSmalltalkFormatter(SymbolicDataAnalysisExpressionSmalltalkFormatter original, Cloner cloner) : base(original, cloner) { }
+    public SymbolicDataAnalysisExpressionSmalltalkFormatter()
+      : base() {
+      Name = ItemName;
+      Description = ItemDescription;
+    }
+
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree) {
+      return FormatRecursively(symbolicExpressionTree.Root);
+    }
+
+    // returns the smalltalk expression corresponding to the node 
+    // smalltalk expressions are always surrounded by parantheses "(<expr>)"
+    private string FormatRecursively(ISymbolicExpressionTreeNode node) {
+
+      ISymbol symbol = node.Symbol;
+
+      if (symbol is ProgramRootSymbol || symbol is StartSymbol)
+        return FormatRecursively(node.GetSubtree(0));
+
+      StringBuilder stringBuilder = new StringBuilder(20);
+
+      stringBuilder.Append("(");
+
+      if (symbol is Addition) {
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("+");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+        }
+      } else if (symbol is And) {
+        stringBuilder.Append("(");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("&");
+          stringBuilder.Append("(");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          stringBuilder.Append(" > 0)");
+        }
+        stringBuilder.Append(") ifTrue:[1] ifFalse:[-1]");
+      } else if (symbol is Average) {
+        stringBuilder.Append("(1/");
+        stringBuilder.Append(node.SubtreeCount);
+        stringBuilder.Append(")*(");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("+");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+        }
+        stringBuilder.Append(")");
+      } else if (symbol is Constant) {
+        ConstantTreeNode constantTreeNode = node as ConstantTreeNode;
+        stringBuilder.Append(constantTreeNode.Value.ToString(CultureInfo.InvariantCulture));
+      } else if (symbol is Cosine) {
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" cos");
+      } else if (symbol is Division) {
+        if (node.SubtreeCount == 1) {
+          stringBuilder.Append("1/");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        } else {
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+          stringBuilder.Append("/(");
+          for (int i = 1; i < node.SubtreeCount; i++) {
+            if (i > 1) stringBuilder.Append("*");
+            stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          }
+          stringBuilder.Append(")");
+        }
+      } else if (symbol is Exponential) {
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" exp");
+      } else if (symbol is GreaterThan) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" > ");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append(") ifTrue: [1] ifFalse: [-1]");
+      } else if (symbol is IfThenElse) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" > 0) ifTrue: [");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append("] ifFalse: [");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(2)));
+        stringBuilder.Append("]");
+      } else if (symbol is LaggedVariable) {
+        stringBuilder.Append("lagged variables are not supported");
+      } else if (symbol is LessThan) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" < ");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(1)));
+        stringBuilder.Append(") ifTrue: [1] ifFalse: [-1]");
+      } else if (symbol is Logarithm) {
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append("ln");
+      } else if (symbol is Multiplication) {
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("*");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+        }
+      } else if (symbol is Not) {
+        stringBuilder.Append("(");
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(">0) ifTrue: [-1] ifFalse: [1.0]");
+      } else if (symbol is Or) {
+        stringBuilder.Append("(");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append("|");
+          stringBuilder.Append("(");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          stringBuilder.Append(">0)");
+        }
+        stringBuilder.Append(") ifTrue:[1] ifFalse:[-1]");
+      } else if (symbol is Sine) {
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" sin");
+      } else if (symbol is Subtraction) {
+        if (node.SubtreeCount == 1) {
+          stringBuilder.Append("-1*");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        } else {
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+          for (int i = 1; i < node.SubtreeCount; i++) {
+            stringBuilder.Append(" - ");
+            stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+          }
+        }
+      } else if (symbol is Tangent) {
+        stringBuilder.Append(FormatRecursively(node.GetSubtree(0)));
+        stringBuilder.Append(" tan");
+      } else if (symbol is Variable) {
+        VariableTreeNode variableTreeNode = node as VariableTreeNode;
+        stringBuilder.Append(variableTreeNode.Weight.ToString(CultureInfo.InvariantCulture));
+        stringBuilder.Append("*");
+        stringBuilder.Append(variableTreeNode.VariableName);
+      } else if (symbol is BinaryFactorVariable || symbol is FactorVariable) {
+        stringBuilder.Append("factor variables are not supported");
+      } else {
+        stringBuilder.Append("(");
+        for (int i = 0; i < node.SubtreeCount; i++) {
+          if (i > 0) stringBuilder.Append(", ");
+          stringBuilder.Append(FormatRecursively(node.GetSubtree(i)));
+        }
+        stringBuilder.AppendFormat(" {0} [Not Supported] )", node.Symbol.Name);
+      }
+
+      stringBuilder.Append(")");
+
+      return stringBuilder.ToString();
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionSmalltalkFormatter(this, cloner);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/TSQLExpressionFormatter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/TSQLExpressionFormatter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Formatters/TSQLExpressionFormatter.cs	(revision 16337)
@@ -0,0 +1,278 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  internal static class StringBuilderExtensions {
+    internal static void AppendIndented(this StringBuilder strBuilder, int level, string text) {
+      strBuilder.Append(new string(' ', level * 2));
+      strBuilder.Append(text);
+    }
+    internal static void AppendLineIndented(this StringBuilder strBuilder, int level, string text) {
+      strBuilder.Append(new string(' ', level * 2));
+      strBuilder.AppendLine(text);
+    }
+  }
+
+  [Item("TSQL String Formatter", "String formatter for string representations of symbolic data analysis expressions in TSQL syntax.")]
+  [StorableClass]
+  public sealed class TSQLExpressionFormatter : NamedItem, ISymbolicExpressionTreeStringFormatter {
+    [StorableConstructor]
+    private TSQLExpressionFormatter(bool deserializing) : base(deserializing) { }
+    private TSQLExpressionFormatter(TSQLExpressionFormatter original, Cloner cloner) : base(original, cloner) { }
+    public TSQLExpressionFormatter()
+      : base() {
+      Name = ItemName;
+      Description = ItemDescription;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new TSQLExpressionFormatter(this, cloner);
+    }
+
+    public string Format(ISymbolicExpressionTree symbolicExpressionTree) {
+      // skip root and start symbols
+      StringBuilder strBuilder = new StringBuilder();
+      GenerateHeader(strBuilder, symbolicExpressionTree);
+
+      //generate function body
+      FormatRecursively(1, symbolicExpressionTree.Root.GetSubtree(0).GetSubtree(0), strBuilder);
+
+      GenerateFooter(strBuilder);
+      return strBuilder.ToString();
+    }
+
+    private void GenerateHeader(StringBuilder strBuilder, ISymbolicExpressionTree symbolicExpressionTree) {
+      HashSet<string> floatVarNames = new HashSet<string>();
+      foreach (var node in symbolicExpressionTree.IterateNodesPostfix().Where(x => x is VariableTreeNode || x is VariableConditionTreeNode)) {
+        floatVarNames.Add(((IVariableTreeNode)node).VariableName);
+      }
+      var sortedFloatIdentifiers = floatVarNames.OrderBy(n => n, new NaturalStringComparer()).Select(n => VariableName2Identifier(n)).ToList();
+
+      HashSet<string> varcharVarNames = new HashSet<string>();
+      foreach (var node in symbolicExpressionTree.IterateNodesPostfix().Where(x => x is BinaryFactorVariableTreeNode || x is FactorVariableTreeNode)) {
+        varcharVarNames.Add(((IVariableTreeNode)node).VariableName);
+      }
+      var sortedVarcharIdentifiers = varcharVarNames.OrderBy(n => n, new NaturalStringComparer()).Select(n => VariableName2Identifier(n)).ToList();
+
+      //Generate comment and instructions
+      strBuilder.Append("-- generated. created function can be used like 'SELECT dbo.REGRESSIONMODEL(");
+      strBuilder.Append(string.Join(", ", sortedVarcharIdentifiers));
+      if (varcharVarNames.Any() && floatVarNames.Any())
+        strBuilder.Append(",");
+      strBuilder.Append(string.Join(", ", sortedFloatIdentifiers));
+      strBuilder.AppendLine(")'");
+      strBuilder.AppendLine("-- use the expression after the RETURN statement if you want to incorporate the model in a query without creating a function.");
+
+      //Generate function header
+      strBuilder.Append("CREATE FUNCTION dbo.REGRESSIONMODEL(");
+      strBuilder.Append(string.Join(", ", sortedVarcharIdentifiers.Select(n => string.Format("{0} NVARCHAR(max)",n))));
+      if (varcharVarNames.Any() && floatVarNames.Any())
+        strBuilder.Append(",");
+      strBuilder.Append(string.Join(", ", sortedFloatIdentifiers.Select(n => string.Format("{0} FLOAT",n))));
+      strBuilder.AppendLine(")");
+
+      //start function body
+      strBuilder.AppendLine("RETURNS FLOAT");
+      strBuilder.AppendLine("BEGIN");
+
+      //add variable declaration for convenience
+      strBuilder.AppendLineIndented(1, "-- added variable declaration for convenience");
+      foreach (var name in sortedVarcharIdentifiers)
+        strBuilder.AppendLineIndented(1, string.Format("-- DECLARE {0} NVARCHAR(max) = ''", name));
+      foreach (var name in sortedFloatIdentifiers)
+        strBuilder.AppendLineIndented(1, string.Format("-- DECLARE {0} FLOAT = 0.0", name));
+      strBuilder.AppendLineIndented(1, "-- SELECT");
+      strBuilder.AppendLine("RETURN ");
+    }
+
+    private void FormatRecursively(int level, ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.Subtrees.Any()) {
+        if (node.Symbol is Addition) {
+          FormatOperator(level, node, "+", strBuilder);
+        } else if (node.Symbol is And) {
+          FormatOperator(level, node, "AND", strBuilder);
+        } else if (node.Symbol is Average) {
+          FormatAverage(level, node, strBuilder);
+        } else if (node.Symbol is Cosine) {
+          FormatFunction(level, node, "COS", strBuilder);
+        } else if (node.Symbol is Division) {
+          FormatDivision(level, node, strBuilder);
+        } else if (node.Symbol is Exponential) {
+          FormatFunction(level, node, "EXP", strBuilder);
+        } else if (node.Symbol is GreaterThan) {
+          FormatOperator(level, node, ">", strBuilder);
+        } else if (node.Symbol is IfThenElse) {
+          FormatIfThenElse(level, node, strBuilder);
+        } else if (node.Symbol is LessThan) {
+          FormatOperator(level, node, "<", strBuilder);
+        } else if (node.Symbol is Logarithm) {
+          FormatFunction(level, node, "LOG", strBuilder);
+        } else if (node.Symbol is Multiplication) {
+          FormatOperator(level, node, "*", strBuilder);
+        } else if (node.Symbol is Not) {
+          FormatOperator(level, node, "NOT LIKE", strBuilder);
+        } else if (node.Symbol is Or) {
+          FormatOperator(level, node, "OR", strBuilder);
+        } else if (node.Symbol is Xor) {
+          throw new NotSupportedException(string.Format("Symbol {0} not yet supported.", node.Symbol.GetType().Name));
+        } else if (node.Symbol is Sine) {
+          FormatFunction(level, node, "SIN", strBuilder);
+        } else if (node.Symbol is Subtraction) {
+          FormatSubtraction(level, node, strBuilder);
+        } else if (node.Symbol is Tangent) {
+          FormatFunction(level, node, "TAN", strBuilder);
+        } else if (node.Symbol is Square) {
+          FormatFunction(level, node, "SQUARE", strBuilder);
+        } else if (node.Symbol is SquareRoot) {
+          FormatFunction(level, node, "SQRT", strBuilder);
+        } else if (node.Symbol is Power) {
+          FormatFunction(level, node, "POWER", strBuilder);
+        } else if (node.Symbol is Root) {
+          FormatRoot(level, node, strBuilder);
+        } else {
+          throw new NotSupportedException("Formatting of symbol: " + node.Symbol + " not supported for TSQL symbolic expression tree formatter.");
+        }
+      } else {
+        if (node is VariableTreeNode) {
+          var varNode = node as VariableTreeNode;
+          strBuilder.AppendFormat("{0} * {1}", VariableName2Identifier(varNode.VariableName), varNode.Weight.ToString("g17", CultureInfo.InvariantCulture));
+        } else if (node is ConstantTreeNode) {
+          var constNode = node as ConstantTreeNode;
+          strBuilder.Append(constNode.Value.ToString("g17", CultureInfo.InvariantCulture));
+        } else if (node.Symbol is FactorVariable) {
+          var factorNode = node as FactorVariableTreeNode;
+          FormatFactor(level, factorNode, strBuilder);
+        } else if (node.Symbol is BinaryFactorVariable) {
+          var binFactorNode = node as BinaryFactorVariableTreeNode;
+          throw new NotSupportedException(string.Format("Symbol {0} not yet supported.", node.Symbol.GetType().Name));
+        } else {
+          throw new NotSupportedException("Formatting of symbol: " + node.Symbol + " not supported for TSQL symbolic expression tree formatter.");
+        }
+      }
+    }
+
+    private void FormatIfThenElse(int level, ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("CASE ISNULL((SELECT 1 WHERE");
+      FormatRecursively(level,node.GetSubtree(0), strBuilder);
+      strBuilder.AppendLine("),0)");
+      strBuilder.AppendIndented(level,"WHEN 1 THEN ");
+      FormatRecursively(level, node.GetSubtree(1), strBuilder);
+      strBuilder.AppendLine();
+      strBuilder.AppendIndented(level, "WHEN 0 THEN ");
+      FormatRecursively(level, node.GetSubtree(2), strBuilder);
+      strBuilder.AppendLine();
+      strBuilder.AppendIndented(level, "END");
+    }
+
+    private void FormatAverage(int level, ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.Append("(");
+      foreach (var child in node.Subtrees) {
+        FormatRecursively(level, child, strBuilder);
+        if (child != node.Subtrees.Last())
+          strBuilder.Append(" + ");
+      }
+      strBuilder.AppendFormat(") / {0}", node.Subtrees.Count());
+    }
+
+    private string VariableName2Identifier(string variableName) {
+      return "@"+variableName.Replace(' ', '_');
+    }
+
+    private void GenerateFooter(StringBuilder strBuilder) {
+      strBuilder.Append(Environment.NewLine);
+      strBuilder.AppendLine("END");
+    }
+
+
+    private void FormatOperator(int level, ISymbolicExpressionTreeNode node, string symbol, StringBuilder strBuilder) {
+      strBuilder.Append("(");
+      foreach (var child in node.Subtrees) {
+        FormatRecursively(level, child, strBuilder);
+        if (child != node.Subtrees.Last())
+          strBuilder.Append(" " + symbol + " ");
+      }
+      strBuilder.Append(")");
+    }
+
+    private void FormatFunction(int level, ISymbolicExpressionTreeNode node, string function, StringBuilder strBuilder) {
+      strBuilder.Append(function + "(");
+      foreach (var child in node.Subtrees) {
+        FormatRecursively(level++, child, strBuilder);
+        if (child != node.Subtrees.Last())
+          strBuilder.Append(", ");
+      }
+      strBuilder.Append(")");
+    }
+
+    private void FormatDivision(int level, ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.SubtreeCount == 1) {
+        strBuilder.Append("1.0 / ");
+        FormatRecursively(level, node.GetSubtree(0), strBuilder);
+      } else {
+        FormatRecursively(level, node.GetSubtree(0), strBuilder);
+        strBuilder.Append("/ (");
+        for (int i = 1; i < node.SubtreeCount; i++) {
+          if (i > 1) strBuilder.Append(" * ");
+          FormatRecursively(level, node.GetSubtree(i), strBuilder);
+        }
+        strBuilder.Append(")");
+      }
+    }
+
+    private void FormatSubtraction(int level, ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      if (node.SubtreeCount == 1) {
+        strBuilder.Append("-");
+        FormatRecursively(level, node.GetSubtree(0), strBuilder);
+        return;
+      }
+      //Default case: more than 1 child
+      FormatOperator(level, node, "-", strBuilder);
+    }
+
+    private void FormatRoot(int level, ISymbolicExpressionTreeNode node, StringBuilder strBuilder) {
+      strBuilder.AppendLine("POWER(");
+      FormatRecursively(level, node.GetSubtree(0), strBuilder);
+      strBuilder.AppendLineIndented(level, " , 1.0 / (");
+      FormatRecursively(level, node.GetSubtree(1), strBuilder);
+      strBuilder.AppendLineIndented(level, "))");
+    }
+
+    private void FormatFactor(int level, FactorVariableTreeNode node, StringBuilder strBuilder) {
+      strBuilder.AppendLine("( ");
+      strBuilder.AppendLineIndented(level + 1, string.Format("CASE {0}", VariableName2Identifier(node.VariableName)));
+      foreach (var name in node.Symbol.GetVariableValues(node.VariableName)) {
+        strBuilder.AppendLineIndented(level + 2, string.Format("WHEN '{0}' THEN {1}", name, node.GetValue(name).ToString(CultureInfo.InvariantCulture)));
+      }
+      strBuilder.AppendLineIndented(level + 1, "ELSE NULL END");
+      strBuilder.AppendIndented(level, ")");
+    }
+
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/ArithmeticExpressionGrammar.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/ArithmeticExpressionGrammar.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/ArithmeticExpressionGrammar.cs	(revision 16337)
@@ -0,0 +1,85 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.PluginInfrastructure;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [NonDiscoverableType]
+  [StorableClass]
+  [Item("ArithmeticExpressionGrammar", "Represents a grammar for functional expressions using only arithmetic operations.")]
+  public class ArithmeticExpressionGrammar : SymbolicExpressionGrammar, ISymbolicDataAnalysisGrammar {
+
+    [StorableConstructor]
+    protected ArithmeticExpressionGrammar(bool deserializing) : base(deserializing) { }
+    protected ArithmeticExpressionGrammar(ArithmeticExpressionGrammar original, Cloner cloner) : base(original, cloner) { }
+    public ArithmeticExpressionGrammar()
+      : base(ItemAttribute.GetName(typeof(ArithmeticExpressionGrammar)), ItemAttribute.GetDescription(typeof(ArithmeticExpressionGrammar))) {
+      Initialize();
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new ArithmeticExpressionGrammar(this, cloner);
+    }
+
+    private void Initialize() {
+      var add = new Addition();
+      var sub = new Subtraction();
+      var mul = new Multiplication();
+      var div = new Division();
+      var constant = new Constant();
+      constant.MinValue = -20;
+      constant.MaxValue = 20;
+      var variableSymbol = new HeuristicLab.Problems.DataAnalysis.Symbolic.Variable();
+      var binFactorVariableSymbol = new BinaryFactorVariable();
+      var factorVariableSymbol = new FactorVariable();
+
+      var allSymbols = new List<Symbol>() { add, sub, mul, div, constant, variableSymbol, binFactorVariableSymbol, factorVariableSymbol};
+      var functionSymbols = new List<Symbol>() { add, sub, mul, div };
+
+      foreach (var symb in allSymbols)
+        AddSymbol(symb);
+
+      foreach (var funSymb in functionSymbols) {
+        SetSubtreeCount(funSymb, 1, 3);
+      }
+      SetSubtreeCount(constant, 0, 0);
+      SetSubtreeCount(variableSymbol, 0, 0);
+      SetSubtreeCount(binFactorVariableSymbol, 0, 0);
+      SetSubtreeCount(factorVariableSymbol, 0, 0);
+
+      // allow each symbol as child of the start symbol
+      foreach (var symb in allSymbols) {
+        AddAllowedChildSymbol(StartSymbol, symb);
+        AddAllowedChildSymbol(DefunSymbol, symb);
+      }
+
+      // allow each symbol as child of every other symbol (except for terminals that have maxSubtreeCount == 0)
+      foreach (var parent in functionSymbols) {
+        foreach (var child in allSymbols)
+          AddAllowedChildSymbol(parent, child);
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/FullFunctionalExpressionGrammar.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/FullFunctionalExpressionGrammar.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/FullFunctionalExpressionGrammar.cs	(revision 16337)
@@ -0,0 +1,168 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("FullFunctionalExpressionGrammar", "Represents a grammar for functional expressions using all available functions.")]
+  public class FullFunctionalExpressionGrammar : SymbolicExpressionGrammar, ISymbolicDataAnalysisGrammar {
+    [StorableConstructor]
+    protected FullFunctionalExpressionGrammar(bool deserializing) : base(deserializing) { }
+    protected FullFunctionalExpressionGrammar(FullFunctionalExpressionGrammar original, Cloner cloner) : base(original, cloner) { }
+    public FullFunctionalExpressionGrammar()
+      : base(ItemAttribute.GetName(typeof(FullFunctionalExpressionGrammar)), ItemAttribute.GetDescription(typeof(FullFunctionalExpressionGrammar))) {
+      Initialize();
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new FullFunctionalExpressionGrammar(this, cloner);
+    }
+
+    private void Initialize() {
+      var add = new Addition();
+      var sub = new Subtraction();
+      var mul = new Multiplication();
+      var div = new Division();
+      var mean = new Average();
+      var sin = new Sine();
+      var cos = new Cosine();
+      var tan = new Tangent();
+      var log = new Logarithm();
+      var pow = new Power();
+      pow.InitialFrequency = 0.0;
+      var square = new Square();
+      square.InitialFrequency = 0.0;
+      var root = new Root();
+      root.InitialFrequency = 0.0;
+      var sqrt = new SquareRoot();
+      sqrt.InitialFrequency = 0.0;
+      var airyA = new AiryA();
+      airyA.InitialFrequency = 0.0;
+      var airyB = new AiryB();
+      airyB.InitialFrequency = 0.0;
+      var bessel = new Bessel();
+      bessel.InitialFrequency = 0.0;
+      var cosineIntegral = new CosineIntegral();
+      cosineIntegral.InitialFrequency = 0.0;
+      var dawson = new Dawson();
+      dawson.InitialFrequency = 0.0;
+      var erf = new Erf();
+      erf.InitialFrequency = 0.0;
+      var expIntegralEi = new ExponentialIntegralEi();
+      expIntegralEi.InitialFrequency = 0.0;
+      var fresnelCosineIntegral = new FresnelCosineIntegral();
+      fresnelCosineIntegral.InitialFrequency = 0.0;
+      var fresnelSineIntegral = new FresnelSineIntegral();
+      fresnelSineIntegral.InitialFrequency = 0.0;
+      var gamma = new Gamma();
+      gamma.InitialFrequency = 0.0;
+      var hypCosineIntegral = new HyperbolicCosineIntegral();
+      hypCosineIntegral.InitialFrequency = 0.0;
+      var hypSineIntegral = new HyperbolicSineIntegral();
+      hypSineIntegral.InitialFrequency = 0.0;
+      var norm = new Norm();
+      norm.InitialFrequency = 0.0;
+      var psi = new Psi();
+      psi.InitialFrequency = 0.0;
+      var sineIntegral = new SineIntegral();
+      sineIntegral.InitialFrequency = 0.0;
+
+      var exp = new Exponential();
+      var @if = new IfThenElse();
+      var gt = new GreaterThan();
+      var lt = new LessThan();
+      var and = new And();
+      var or = new Or();
+      var not = new Not();
+      var xor = new Xor();
+
+      var timeLag = new TimeLag();
+      timeLag.InitialFrequency = 0.0;
+      var integral = new Integral();
+      integral.InitialFrequency = 0.0;
+      var derivative = new Derivative();
+      derivative.InitialFrequency = 0.0;
+
+      var variableCondition = new VariableCondition();
+      variableCondition.InitialFrequency = 0.0;
+
+      var constant = new Constant();
+      constant.MinValue = -20;
+      constant.MaxValue = 20;
+      var variableSymbol = new HeuristicLab.Problems.DataAnalysis.Symbolic.Variable();
+      var binFactorVariable = new BinaryFactorVariable();
+      var factorVariable = new FactorVariable();
+      var laggedVariable = new LaggedVariable();
+      laggedVariable.InitialFrequency = 0.0;
+      var autoregressiveVariable = new AutoregressiveTargetVariable();
+      autoregressiveVariable.InitialFrequency = 0.0;
+      autoregressiveVariable.Enabled = false;
+
+      var allSymbols = new List<Symbol>() { add, sub, mul, div, mean, sin, cos, tan, log, square, pow, sqrt, root, exp,
+        airyA, airyB, bessel, cosineIntegral, dawson, erf, expIntegralEi, fresnelCosineIntegral, fresnelSineIntegral, gamma, hypCosineIntegral, hypSineIntegral, norm, psi, sineIntegral,
+        @if, gt, lt, and, or, not,xor, timeLag, integral, derivative, constant, variableSymbol, binFactorVariable, factorVariable, laggedVariable,autoregressiveVariable, variableCondition };
+      var unaryFunctionSymbols = new List<Symbol>() { square, sqrt, sin, cos, tan, log, exp, not, timeLag, integral, derivative,
+        airyA, airyB, bessel, cosineIntegral, dawson, erf, expIntegralEi, fresnelCosineIntegral, fresnelSineIntegral, gamma, hypCosineIntegral, hypSineIntegral, norm, psi, sineIntegral
+      };
+
+      var binaryFunctionSymbols = new List<Symbol>() { pow, root, gt, lt, variableCondition };
+      var ternarySymbols = new List<Symbol>() { add, sub, mul, div, mean, and, or, xor };
+      var terminalSymbols = new List<Symbol>() { variableSymbol, binFactorVariable, factorVariable, constant, laggedVariable, autoregressiveVariable };
+
+      foreach (var symb in allSymbols)
+        AddSymbol(symb);
+
+      foreach (var funSymb in ternarySymbols) {
+        SetSubtreeCount(funSymb, 1, 3);
+      }
+      foreach (var funSymb in unaryFunctionSymbols) {
+        SetSubtreeCount(funSymb, 1, 1);
+      }
+      foreach (var funSymb in binaryFunctionSymbols) {
+        SetSubtreeCount(funSymb, 2, 2);
+      }
+      foreach (var terminalSymbol in terminalSymbols) {
+        SetSubtreeCount(terminalSymbol, 0, 0);
+      }
+
+      SetSubtreeCount(@if, 3, 3);
+
+
+      // allow each symbol as child of the start symbol
+      foreach (var symb in allSymbols) {
+        AddAllowedChildSymbol(StartSymbol, symb);
+        AddAllowedChildSymbol(DefunSymbol, symb);
+      }
+
+      // allow each symbol as child of every other symbol (except for terminals that have maxSubtreeCount == 0)
+      foreach (var parent in allSymbols.Except(terminalSymbols)) {
+        foreach (var child in allSymbols)
+          AddAllowedChildSymbol(parent, child);
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/TypeCoherentExpressionGrammar.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/TypeCoherentExpressionGrammar.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Grammars/TypeCoherentExpressionGrammar.cs	(revision 16337)
@@ -0,0 +1,265 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("TypeCoherentExpressionGrammar", "Represents a grammar for functional expressions in which special syntactic constraints are enforced so that boolean and real-valued expressions are not mixed.")]
+  public class TypeCoherentExpressionGrammar : SymbolicExpressionGrammar, ISymbolicDataAnalysisGrammar {
+    private const string ArithmeticFunctionsName = "Arithmetic Functions";
+    private const string TrigonometricFunctionsName = "Trigonometric Functions";
+    private const string ExponentialFunctionsName = "Exponential and Logarithmic Functions";
+    private const string RealValuedSymbolsName = "Real Valued Symbols";
+    private const string TerminalsName = "Terminals";
+    private const string PowerFunctionsName = "Power Functions";
+    private const string ConditionsName = "Conditions";
+    private const string ComparisonsName = "Comparisons";
+    private const string BooleanOperatorsName = "Boolean Operators";
+    private const string ConditionalSymbolsName = "ConditionalSymbols";
+    private const string SpecialFunctionsName = "Special Functions";
+    private const string TimeSeriesSymbolsName = "Time Series Symbols";
+
+    [StorableConstructor]
+    protected TypeCoherentExpressionGrammar(bool deserializing) : base(deserializing) { }
+    protected TypeCoherentExpressionGrammar(TypeCoherentExpressionGrammar original, Cloner cloner) : base(original, cloner) { }
+    public TypeCoherentExpressionGrammar()
+      : base(ItemAttribute.GetName(typeof(TypeCoherentExpressionGrammar)), ItemAttribute.GetDescription(typeof(TypeCoherentExpressionGrammar))) {
+      Initialize();
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new TypeCoherentExpressionGrammar(this, cloner);
+    }
+
+    private void Initialize() {
+      #region symbol declaration
+      var add = new Addition();
+      var sub = new Subtraction();
+      var mul = new Multiplication();
+      var div = new Division();
+      var mean = new Average();
+      var sin = new Sine();
+      var cos = new Cosine();
+      var tan = new Tangent();
+      var log = new Logarithm();
+      var pow = new Power();
+      var square = new Square();
+      var root = new Root();
+      var sqrt = new SquareRoot();
+      var exp = new Exponential();
+
+      var airyA = new AiryA();
+      var airyB = new AiryB();
+      var bessel = new Bessel();
+      var cosineIntegral = new CosineIntegral();
+      var dawson = new Dawson();
+      var erf = new Erf();
+      var expIntegralEi = new ExponentialIntegralEi();
+      var fresnelCosineIntegral = new FresnelCosineIntegral();
+      var fresnelSineIntegral = new FresnelSineIntegral();
+      var gamma = new Gamma();
+      var hypCosineIntegral = new HyperbolicCosineIntegral();
+      var hypSineIntegral = new HyperbolicSineIntegral();
+      var norm = new Norm();
+      var psi = new Psi();
+      var sineIntegral = new SineIntegral();
+
+      var @if = new IfThenElse();
+      var gt = new GreaterThan();
+      var lt = new LessThan();
+      var and = new And();
+      var or = new Or();
+      var not = new Not();
+      var xor = new Xor();
+      var variableCondition = new VariableCondition();
+
+      var timeLag = new TimeLag();
+      var integral = new Integral();
+      var derivative = new Derivative();
+
+      var constant = new Constant();
+      constant.MinValue = -20;
+      constant.MaxValue = 20;
+      var variableSymbol = new Variable();
+      var binFactorVariable = new BinaryFactorVariable();
+      var factorVariable = new FactorVariable();
+      var laggedVariable = new LaggedVariable();
+      var autoregressiveVariable = new AutoregressiveTargetVariable();
+      #endregion
+
+      #region group symbol declaration
+      var arithmeticSymbols = new GroupSymbol(ArithmeticFunctionsName, new List<ISymbol>() { add, sub, mul, div, mean });
+      var trigonometricSymbols = new GroupSymbol(TrigonometricFunctionsName, new List<ISymbol>() { sin, cos, tan });
+      var exponentialAndLogarithmicSymbols = new GroupSymbol(ExponentialFunctionsName, new List<ISymbol> { exp, log });
+      var specialFunctions = new GroupSymbol(SpecialFunctionsName, new List<ISymbol> { airyA, airyB, bessel, cosineIntegral, dawson, erf, expIntegralEi,
+        fresnelCosineIntegral,fresnelSineIntegral,gamma,hypCosineIntegral,hypSineIntegral,norm, psi, sineIntegral});
+      var terminalSymbols = new GroupSymbol(TerminalsName, new List<ISymbol> { constant, variableSymbol, binFactorVariable, factorVariable });
+      var realValuedSymbols = new GroupSymbol(RealValuedSymbolsName, new List<ISymbol>() { arithmeticSymbols, trigonometricSymbols, exponentialAndLogarithmicSymbols, specialFunctions, terminalSymbols });
+
+      var powerSymbols = new GroupSymbol(PowerFunctionsName, new List<ISymbol> { square, pow, sqrt, root });
+
+      var conditionSymbols = new GroupSymbol(ConditionsName, new List<ISymbol> { @if, variableCondition });
+      var comparisonSymbols = new GroupSymbol(ComparisonsName, new List<ISymbol> { gt, lt });
+      var booleanOperationSymbols = new GroupSymbol(BooleanOperatorsName, new List<ISymbol> { and, or, not, xor });
+      var conditionalSymbols = new GroupSymbol(ConditionalSymbolsName, new List<ISymbol> { conditionSymbols, comparisonSymbols, booleanOperationSymbols });
+
+      var timeSeriesSymbols = new GroupSymbol(TimeSeriesSymbolsName, new List<ISymbol> { timeLag, integral, derivative, laggedVariable, autoregressiveVariable });
+      #endregion
+
+      AddSymbol(realValuedSymbols);
+      AddSymbol(powerSymbols);
+      AddSymbol(conditionalSymbols);
+      AddSymbol(timeSeriesSymbols);
+
+      #region subtree count configuration
+      SetSubtreeCount(arithmeticSymbols, 2, 2);
+      SetSubtreeCount(trigonometricSymbols, 1, 1);
+      SetSubtreeCount(pow, 2, 2);
+      SetSubtreeCount(root, 2, 2);
+      SetSubtreeCount(square, 1, 1);
+      SetSubtreeCount(sqrt, 1, 1);
+      SetSubtreeCount(exponentialAndLogarithmicSymbols, 1, 1);
+      SetSubtreeCount(specialFunctions, 1, 1);
+      SetSubtreeCount(terminalSymbols, 0, 0);
+
+      SetSubtreeCount(@if, 3, 3);
+      SetSubtreeCount(variableCondition, 2, 2);
+      SetSubtreeCount(comparisonSymbols, 2, 2);
+      SetSubtreeCount(and, 2, 2);
+      SetSubtreeCount(or, 2, 2);
+      SetSubtreeCount(not, 1, 1);
+      SetSubtreeCount(xor, 2, 2);
+
+      SetSubtreeCount(timeLag, 1, 1);
+      SetSubtreeCount(integral, 1, 1);
+      SetSubtreeCount(derivative, 1, 1);
+      SetSubtreeCount(laggedVariable, 0, 0);
+      SetSubtreeCount(autoregressiveVariable, 0, 0);
+      #endregion
+
+      #region allowed child symbols configuration
+      AddAllowedChildSymbol(StartSymbol, realValuedSymbols);
+      AddAllowedChildSymbol(StartSymbol, powerSymbols);
+      AddAllowedChildSymbol(StartSymbol, conditionSymbols);
+      AddAllowedChildSymbol(StartSymbol, timeSeriesSymbols);
+      AddAllowedChildSymbol(StartSymbol, specialFunctions);
+
+      AddAllowedChildSymbol(DefunSymbol, realValuedSymbols);
+      AddAllowedChildSymbol(DefunSymbol, powerSymbols);
+      AddAllowedChildSymbol(DefunSymbol, conditionSymbols);
+      AddAllowedChildSymbol(DefunSymbol, timeSeriesSymbols);
+      AddAllowedChildSymbol(DefunSymbol, specialFunctions);
+
+      AddAllowedChildSymbol(realValuedSymbols, realValuedSymbols);
+      AddAllowedChildSymbol(realValuedSymbols, powerSymbols);
+      AddAllowedChildSymbol(realValuedSymbols, conditionSymbols);
+      AddAllowedChildSymbol(realValuedSymbols, timeSeriesSymbols);
+      AddAllowedChildSymbol(realValuedSymbols, specialFunctions);
+
+      AddAllowedChildSymbol(powerSymbols, variableSymbol, 0);
+      AddAllowedChildSymbol(powerSymbols, laggedVariable, 0);
+      AddAllowedChildSymbol(powerSymbols, autoregressiveVariable, 0);
+      AddAllowedChildSymbol(powerSymbols, constant, 1);
+
+      AddAllowedChildSymbol(square, realValuedSymbols, 0);
+      AddAllowedChildSymbol(square, conditionSymbols, 0);
+      AddAllowedChildSymbol(square, timeSeriesSymbols, 0);
+
+      AddAllowedChildSymbol(sqrt, realValuedSymbols, 0);
+      AddAllowedChildSymbol(sqrt, conditionSymbols, 0);
+      AddAllowedChildSymbol(sqrt, timeSeriesSymbols, 0);
+
+      AddAllowedChildSymbol(@if, comparisonSymbols, 0);
+      AddAllowedChildSymbol(@if, booleanOperationSymbols, 0);
+      AddAllowedChildSymbol(@if, conditionSymbols, 1);
+      AddAllowedChildSymbol(@if, realValuedSymbols, 1);
+      AddAllowedChildSymbol(@if, powerSymbols, 1);
+      AddAllowedChildSymbol(@if, timeSeriesSymbols, 1);
+      AddAllowedChildSymbol(@if, conditionSymbols, 2);
+      AddAllowedChildSymbol(@if, realValuedSymbols, 2);
+      AddAllowedChildSymbol(@if, powerSymbols, 2);
+      AddAllowedChildSymbol(@if, timeSeriesSymbols, 2);
+
+      AddAllowedChildSymbol(booleanOperationSymbols, comparisonSymbols);
+      AddAllowedChildSymbol(comparisonSymbols, realValuedSymbols);
+      AddAllowedChildSymbol(comparisonSymbols, powerSymbols);
+      AddAllowedChildSymbol(comparisonSymbols, conditionSymbols);
+      AddAllowedChildSymbol(comparisonSymbols, timeSeriesSymbols);
+
+      AddAllowedChildSymbol(variableCondition, realValuedSymbols);
+      AddAllowedChildSymbol(variableCondition, powerSymbols);
+      AddAllowedChildSymbol(variableCondition, conditionSymbols);
+      AddAllowedChildSymbol(variableCondition, timeSeriesSymbols);
+
+
+      AddAllowedChildSymbol(timeLag, realValuedSymbols);
+      AddAllowedChildSymbol(timeLag, powerSymbols);
+      AddAllowedChildSymbol(timeLag, conditionSymbols);
+
+      AddAllowedChildSymbol(integral, realValuedSymbols);
+      AddAllowedChildSymbol(integral, powerSymbols);
+      AddAllowedChildSymbol(integral, conditionSymbols);
+
+      AddAllowedChildSymbol(derivative, realValuedSymbols);
+      AddAllowedChildSymbol(derivative, powerSymbols);
+      AddAllowedChildSymbol(derivative, conditionSymbols);
+      #endregion
+    }
+
+    public void ConfigureAsDefaultRegressionGrammar() {
+      Symbols.First(s => s is Average).Enabled = false;
+      Symbols.First(s => s.Name == TrigonometricFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == PowerFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == SpecialFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == ConditionalSymbolsName).Enabled = false;
+      Symbols.First(s => s.Name == TimeSeriesSymbolsName).Enabled = false;
+    }
+
+    public void ConfigureAsDefaultClassificationGrammar() {
+      Symbols.First(s => s is Average).Enabled = false;
+      Symbols.First(s => s is VariableCondition).Enabled = false;
+      Symbols.First(s => s is Xor).Enabled = false;
+      Symbols.First(s => s.Name == TrigonometricFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == ExponentialFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == SpecialFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == PowerFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == TimeSeriesSymbolsName).Enabled = false;
+    }
+
+    public void ConfigureAsDefaultTimeSeriesPrognosisGrammar() {
+      Symbols.First(s => s is Average).Enabled = false;
+      Symbols.First(s => s.Name == TrigonometricFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == PowerFunctionsName).Enabled = false;
+      Symbols.First(s => s.Name == ConditionalSymbolsName).Enabled = false;
+      Symbols.First(s => s.Name == SpecialFunctionsName).Enabled = false;
+
+      Symbols.Single(s => s.Name == "Variable").Enabled = false;
+      Symbols.First(s => s.Name == TimeSeriesSymbolsName).Enabled = true;
+      Symbols.First(s => s is Derivative).Enabled = false;
+      Symbols.First(s => s is Integral).Enabled = false;
+      Symbols.First(s => s is TimeLag).Enabled = false;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/HashExtensions.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/HashExtensions.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/HashExtensions.cs	(revision 16337)
@@ -0,0 +1,237 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class SymbolicExpressionHashExtensions {
+    public sealed class HashNode<T> : IComparable<HashNode<T>>, IEquatable<HashNode<T>> where T : class {
+      public T Data;
+      public int Arity;
+      public int Size;
+      public bool IsCommutative;
+
+      public bool Enabled;
+      public ulong HashValue;           // the initial (fixed) hash value for this individual node/data
+      public ulong CalculatedHashValue; // the calculated hash value (taking into account the children hash values)
+
+      public delegate void SimplifyAction(ref HashNode<T>[] nodes, int i);
+      public SimplifyAction Simplify;
+
+      public IComparer<T> Comparer;
+
+      public bool IsLeaf => Arity == 0;
+
+      public HashNode(IComparer<T> comparer) {
+        Comparer = comparer;
+      }
+
+      private HashNode() { }
+
+      public int CompareTo(HashNode<T> other) {
+        var res = Comparer.Compare(Data, other.Data);
+        return res == 0 ? CalculatedHashValue.CompareTo(other.CalculatedHashValue) : res;
+      }
+
+      public override string ToString() {
+        return $"{Data} {Arity} {Size} {CalculatedHashValue} {Enabled}";
+      }
+
+      public bool Equals(HashNode<T> other) {
+        return CalculatedHashValue.Equals(other.CalculatedHashValue);
+      }
+
+      public override bool Equals(object obj) {
+        var other = obj as HashNode<T>;
+        if (other != null)
+          return Equals(other);
+        return base.Equals(obj);
+      }
+
+      public override int GetHashCode() {
+        return (int)CalculatedHashValue;
+      }
+
+      public static bool operator ==(HashNode<T> a, HashNode<T> b) {
+        return a.Equals(b);
+      }
+
+      public static bool operator !=(HashNode<T> a, HashNode<T> b) {
+        return !a.Equals(b);
+      }
+    }
+
+    public static ulong ComputeHash<T>(this HashNode<T>[] nodes, int i, Func<byte[], ulong> hashFunction) where T : class {
+      var node = nodes[i];
+      const int size = sizeof(ulong);
+      var hashes = new ulong[node.Arity + 1];
+      var bytes = new byte[(node.Arity + 1) * size];
+
+      for (int j = i - 1, k = 0; k < node.Arity; ++k, j -= 1 + nodes[j].Size) {
+        hashes[k] = nodes[j].CalculatedHashValue;
+      }
+      hashes[node.Arity] = node.HashValue;
+      Buffer.BlockCopy(hashes, 0, bytes, 0, bytes.Length);
+      return hashFunction(bytes);
+    }
+
+    // set the enabled state for the whole subtree rooted at this node 
+    public static void SetEnabled<T>(this HashNode<T>[] nodes, int i, bool enabled) where T : class {
+      nodes[i].Enabled = enabled;
+      for (int j = i - nodes[i].Size; j < i; ++j)
+        nodes[j].Enabled = enabled;
+    }
+
+    public static HashNode<T>[] Simplify<T>(this HashNode<T>[] nodes, Func<byte[], ulong> hashFunction) where T : class {
+      var reduced = nodes.UpdateNodeSizes().Reduce().Sort(hashFunction);
+
+      for (int i = 0; i < reduced.Length; ++i) {
+        var node = reduced[i];
+        if (node.IsLeaf) {
+          continue;
+        }
+        node.Simplify?.Invoke(ref reduced, i);
+      }
+      // detect if anything was simplified
+      var count = 0;
+      foreach (var node in reduced) {
+        if (!node.Enabled) { ++count; }
+      }
+      if (count == 0) {
+        return reduced;
+      }
+
+      var simplified = new HashNode<T>[reduced.Length - count];
+      int j = 0;
+      foreach (var node in reduced) {
+        if (node.Enabled) {
+          simplified[j++] = node;
+        }
+      }
+      return simplified.UpdateNodeSizes().Reduce().Sort(hashFunction);
+    }
+
+    public static HashNode<T>[] Sort<T>(this HashNode<T>[] nodes, Func<byte[], ulong> hashFunction) where T : class {
+      int sort(int a, int b) => nodes[a].CompareTo(nodes[b]);
+
+      for (int i = 0; i < nodes.Length; ++i) {
+        var node = nodes[i];
+
+        if (node.IsLeaf) {
+          continue;
+        }
+
+        if (node.IsCommutative) { // only sort when the argument order does not matter
+          var arity = node.Arity;
+          var size = node.Size;
+
+          if (arity == size) { // all child nodes are terminals
+            Array.Sort(nodes, i - size, size);
+          } else { // i have some non-terminal children
+            var sorted = new HashNode<T>[size];
+            var indices = new int[node.Arity];
+            for (int j = i - 1, k = 0; k < node.Arity; j -= 1 + nodes[j].Size, ++k) {
+              indices[k] = j;
+            }
+            Array.Sort(indices, sort);
+
+            int idx = 0;
+            foreach (var j in indices) {
+              var child = nodes[j];
+              if (!child.IsLeaf) { // must copy complete subtree
+                Array.Copy(nodes, j - child.Size, sorted, idx, child.Size);
+                idx += child.Size;
+              }
+              sorted[idx++] = nodes[j];
+            }
+            Array.Copy(sorted, 0, nodes, i - size, size);
+          }
+        }
+        node.CalculatedHashValue = nodes.ComputeHash(i, hashFunction);
+      }
+      return nodes;
+    }
+
+    /// <summary>
+    /// Get a function node's child indicest
+    /// </summary>
+    /// <typeparam name="T">The data type encapsulated by a hash node</typeparam>
+    /// <param name="nodes">An array of hash nodes with up-to-date node sizes</param>
+    /// <param name="i">The index in the array of hash nodes of the node whose children we want to iterate</param>
+    /// <returns>An array containing child indices</returns>
+    public static int[] IterateChildren<T>(this HashNode<T>[] nodes, int i) where T : class {
+      var node = nodes[i];
+      var arity = node.Arity;
+      var children = new int[arity];
+      var idx = i - 1;
+      for (int j = 0; j < arity; ++j) {
+        children[j] = idx;
+        idx -= 1 + nodes[idx].Size;
+      }
+      return children;
+    }
+
+    public static HashNode<T>[] UpdateNodeSizes<T>(this HashNode<T>[] nodes) where T : class {
+      for (int i = 0; i < nodes.Length; ++i) {
+        var node = nodes[i];
+        if (node.IsLeaf) {
+          node.Size = 0;
+          continue;
+        }
+        node.Size = node.Arity;
+
+        for (int j = i - 1, k = 0; k < node.Arity; j -= 1 + nodes[j].Size, ++k) {
+          node.Size += nodes[j].Size;
+        }
+      }
+      return nodes;
+    }
+
+    private static HashNode<T>[] Reduce<T>(this HashNode<T>[] nodes) where T : class {
+      int count = 0;
+      for (int i = 0; i < nodes.Length; ++i) {
+        var node = nodes[i];
+        if (node.IsLeaf || !node.IsCommutative) {
+          continue;
+        }
+
+        var arity = node.Arity;
+        for (int j = i - 1, k = 0; k < arity; j -= 1 + nodes[j].Size, ++k) {
+          if (node.HashValue == nodes[j].HashValue) {
+            nodes[j].Enabled = false;
+            node.Arity += nodes[j].Arity - 1;
+            ++count;
+          }
+        }
+      }
+      if (count == 0)
+        return nodes;
+
+      var reduced = new HashNode<T>[nodes.Length - count];
+      var idx = 0;
+      foreach (var node in nodes) {
+        if (node.Enabled) { reduced[idx++] = node; }
+      }
+      return reduced.UpdateNodeSizes();
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/HashUtil.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/HashUtil.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/HashUtil.cs	(revision 16337)
@@ -0,0 +1,92 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+
+using System;
+using System.Security.Cryptography;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class HashUtil {
+    // This class contains some hash functions adapted from http://partow.net/programming/hashfunctions/index.html#AvailableHashFunctions
+
+    // A simple hash function from Robert Sedgwicks Algorithms in C book.I've added some simple optimizations to the algorithm in order to speed up its hashing process. 
+    public static ulong RSHash(byte[] input) {
+      const int b = 378551;
+      ulong a = 63689;
+      ulong hash = 0;
+
+      foreach (var v in input) {
+        hash = (hash * a) + v;
+        a *= b;
+      }
+      return hash;
+    }
+
+    // A bitwise hash function written by Justin Sobel
+    public static ulong JSHash(byte[] input) {
+      ulong hash = 1315423911;
+      for (int i = 0; i < input.Length; ++i)
+        hash ^= (hash << 5) + input[i] + (hash >> 2);
+      return hash;
+    }
+
+    // This hash function comes from Brian Kernighan and Dennis Ritchie's book "The C Programming Language". It is a simple hash function using a strange set of possible seeds which all constitute a pattern of 31....31...31 etc, it seems to be very similar to the DJB hash function. 
+    public static ulong BKDRHash(byte[] input) {
+      ulong seed = 131;
+      ulong hash = 0;
+      foreach (var v in input) {
+        hash = (hash * seed) + v;
+      }
+      return hash;
+    }
+
+    // This is the algorithm of choice which is used in the open source SDBM project. The hash function seems to have a good over-all distribution for many different data sets. It seems to work well in situations where there is a high variance in the MSBs of the elements in a data set. 
+    public static ulong SDBMHash(byte[] input) {
+      ulong hash = 0;
+      foreach (var v in input) {
+        hash = v + (hash << 6) + (hash << 16) - hash;
+      }
+      return hash;
+    }
+
+    // An algorithm produced by Professor Daniel J. Bernstein and shown first to the world on the usenet newsgroup comp.lang.c. It is one of the most efficient hash functions ever published. 
+    public static ulong DJBHash(byte[] input) {
+      ulong hash = 5381;
+      foreach (var v in input) {
+        hash = (hash << 5) + hash + v;
+      }
+      return hash;
+    }
+
+    // An algorithm proposed by Donald E.Knuth in The Art Of Computer Programming Volume 3, under the topic of sorting and search chapter 6.4. 
+    public static ulong DEKHash(byte[] input) {
+      ulong hash = (ulong)input.Length;
+      foreach (var v in input) {
+        hash = (hash << 5) ^ (hash >> 27) ^ v;
+      }
+      return hash;
+    }
+
+    public static ulong CryptoHash(HashAlgorithm ha, byte[] input) {
+      return BitConverter.ToUInt64(ha.ComputeHash(input), 0);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/SymbolicExpressionTreeHash.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/SymbolicExpressionTreeHash.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Hashing/SymbolicExpressionTreeHash.cs	(revision 16337)
@@ -0,0 +1,363 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Linq;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using static HeuristicLab.Problems.DataAnalysis.Symbolic.SymbolicExpressionHashExtensions;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class SymbolicExpressionTreeHash {
+    private static readonly Addition add = new Addition();
+    private static readonly Subtraction sub = new Subtraction();
+    private static readonly Multiplication mul = new Multiplication();
+    private static readonly Division div = new Division();
+    private static readonly Logarithm log = new Logarithm();
+    private static readonly Exponential exp = new Exponential();
+    private static readonly Sine sin = new Sine();
+    private static readonly Cosine cos = new Cosine();
+    private static readonly Constant constant = new Constant();
+
+    private static readonly ISymbolicExpressionTreeNodeComparer comparer = new SymbolicExpressionTreeNodeComparer();
+
+    public static ulong ComputeHash(this ISymbolicExpressionTree tree) {
+      return ComputeHash(tree.Root.GetSubtree(0).GetSubtree(0));
+    }
+
+    public static double ComputeSimilarity(ISymbolicExpressionTree t1, ISymbolicExpressionTree t2, bool simplify = false) {
+      return ComputeSimilarity(t1.Root.GetSubtree(0).GetSubtree(0), t2.Root.GetSubtree(0).GetSubtree(0), simplify);
+    }
+
+    public static double ComputeSimilarity(ISymbolicExpressionTreeNode t1, ISymbolicExpressionTreeNode t2, bool simplify = false) {
+      HashNode<ISymbolicExpressionTreeNode>[] lhs;
+      HashNode<ISymbolicExpressionTreeNode>[] rhs;
+
+      ulong hashFunction(byte[] input) => HashUtil.DJBHash(input);
+
+      if (simplify) {
+        lhs = t1.MakeNodes().Simplify(hashFunction);
+        rhs = t2.MakeNodes().Simplify(hashFunction);
+      } else {
+        lhs = t1.MakeNodes().Sort(hashFunction); // sort calculates hash values
+        rhs = t2.MakeNodes().Sort(hashFunction);
+      }
+
+      var lh = lhs.Select(x => x.CalculatedHashValue).ToArray();
+      var rh = rhs.Select(x => x.CalculatedHashValue).ToArray();
+
+      Array.Sort(lh);
+      Array.Sort(rh);
+
+      return ComputeSimilarity(lh, rh);
+    }
+
+    // this will only work if lh and rh are sorted 
+    private static double ComputeSimilarity(ulong[] lh, ulong[] rh) {
+      double count = 0;
+      for (int i = 0, j = 0; i < lh.Length && j < rh.Length;) {
+        var h1 = lh[i];
+        var h2 = rh[j];
+        if (h1 == h2) {
+          ++count;
+          ++i;
+          ++j;
+        } else if (h1 < h2) {
+          ++i;
+        } else if (h1 > h2) {
+          ++j;
+        }
+      }
+
+      return 2d * count / (lh.Length + rh.Length);
+    }
+
+    public static double ComputeAverageSimilarity(ISymbolicExpressionTree[] trees, bool simplify = false, bool strict = false) {
+      var total = (double)trees.Length * (trees.Length - 1) / 2;
+      double avg = 0;
+      var hashes = new ulong[trees.Length][];
+      // build hash arrays
+      for (int i = 0; i < trees.Length; ++i) {
+        var nodes = trees[i].MakeNodes(strict);
+        hashes[i] = (simplify ? nodes.Simplify(HashUtil.DJBHash) : nodes.Sort(HashUtil.DJBHash)).Select(x => x.CalculatedHashValue).ToArray();
+        Array.Sort(hashes[i]);
+      }
+      // compute similarity matrix
+      for (int i = 0; i < trees.Length - 1; ++i) {
+        for (int j = i + 1; j < trees.Length; ++j) {
+          avg += ComputeSimilarity(hashes[i], hashes[j]);
+        }
+      }
+      return avg / total;
+    }
+
+    public static double[,] ComputeSimilarityMatrix(ISymbolicExpressionTree[] trees, bool simplify = false, bool strict = false) {
+      var sim = new double[trees.Length, trees.Length];
+      var hashes = new ulong[trees.Length][];
+      // build hash arrays
+      for (int i = 0; i < trees.Length; ++i) {
+        var nodes = trees[i].MakeNodes(strict);
+        hashes[i] = (simplify ? nodes.Simplify(HashUtil.DJBHash) : nodes.Sort(HashUtil.DJBHash)).Select(x => x.CalculatedHashValue).ToArray();
+        Array.Sort(hashes[i]);
+      }
+      // compute similarity matrix
+      for (int i = 0; i < trees.Length - 1; ++i) {
+        for (int j = i + 1; j < trees.Length; ++j) {
+          sim[i, j] = sim[j, i] = ComputeSimilarity(hashes[i], hashes[j]);
+        }
+      }
+      return sim;
+    }
+
+    public static ulong ComputeHash(this ISymbolicExpressionTreeNode treeNode, bool strict = false) {
+      ulong hashFunction(byte[] input) => HashUtil.JSHash(input);
+      var hashNodes = treeNode.MakeNodes(strict);
+      var simplified = hashNodes.Simplify(hashFunction);
+      return simplified.Last().CalculatedHashValue;
+    }
+
+    public static HashNode<ISymbolicExpressionTreeNode> ToHashNode(this ISymbolicExpressionTreeNode node, bool strict = false) {
+      var symbol = node.Symbol;
+      var name = symbol.Name;
+      if (node is ConstantTreeNode constantNode) {
+        name = strict ? constantNode.Value.ToString() : symbol.Name;
+      } else if (node is VariableTreeNode variableNode) {
+        name = strict ? variableNode.Weight.ToString() + variableNode.VariableName : variableNode.VariableName;
+      }
+      var hash = (ulong)name.GetHashCode();
+      var hashNode = new HashNode<ISymbolicExpressionTreeNode>(comparer) {
+        Data = node,
+        Arity = node.SubtreeCount,
+        Size = node.SubtreeCount,
+        IsCommutative = node.Symbol is Addition || node.Symbol is Multiplication,
+        Enabled = true,
+        HashValue = hash,
+        CalculatedHashValue = hash
+      };
+      if (symbol is Addition) {
+        hashNode.Simplify = SimplifyAddition;
+      } else if (symbol is Multiplication) {
+        hashNode.Simplify = SimplifyMultiplication;
+      } else if (symbol is Division) {
+        hashNode.Simplify = SimplifyDivision;
+      } else if (symbol is Logarithm || symbol is Exponential || symbol is Sine || symbol is Cosine) {
+        hashNode.Simplify = SimplifyUnaryNode;
+      } else if (symbol is Subtraction) {
+        hashNode.Simplify = SimplifyBinaryNode;
+      }
+      return hashNode;
+    }
+
+    public static HashNode<ISymbolicExpressionTreeNode>[] MakeNodes(this ISymbolicExpressionTree tree, bool strict = false) {
+      return MakeNodes(tree.Root.GetSubtree(0).GetSubtree(0), strict);
+    }
+
+    public static HashNode<ISymbolicExpressionTreeNode>[] MakeNodes(this ISymbolicExpressionTreeNode node, bool strict = false) {
+      return node.IterateNodesPostfix().Select(x => x.ToHashNode(strict)).ToArray().UpdateNodeSizes();
+    }
+
+    #region parse a nodes array back into a tree
+    public static ISymbolicExpressionTree ToTree(this HashNode<ISymbolicExpressionTreeNode>[] nodes) {
+      var root = new ProgramRootSymbol().CreateTreeNode();
+      var start = new StartSymbol().CreateTreeNode();
+      root.AddSubtree(start);
+      start.AddSubtree(nodes.ToSubtree());
+      return new SymbolicExpressionTree(root);
+    }
+
+    public static ISymbolicExpressionTreeNode ToSubtree(this HashNode<ISymbolicExpressionTreeNode>[] nodes) {
+      var treeNodes = nodes.Select(x => x.Data.Symbol.CreateTreeNode()).ToArray();
+
+      for (int i = nodes.Length - 1; i >= 0; --i) {
+        var node = nodes[i];
+
+        if (node.IsLeaf) {
+          if (node.Data is VariableTreeNode variable) {
+            var variableTreeNode = (VariableTreeNode)treeNodes[i];
+            variableTreeNode.VariableName = variable.VariableName;
+            variableTreeNode.Weight = variable.Weight;
+          } else if (node.Data is ConstantTreeNode @const) {
+            var constantTreeNode = (ConstantTreeNode)treeNodes[i];
+            constantTreeNode.Value = @const.Value;
+          }
+          continue;
+        }
+
+        var treeNode = treeNodes[i];
+
+        foreach (var j in nodes.IterateChildren(i)) {
+          treeNode.AddSubtree(treeNodes[j]);
+        }
+      }
+
+      return treeNodes.Last();
+    }
+
+    private static T CreateTreeNode<T>(this ISymbol symbol) where T : class, ISymbolicExpressionTreeNode {
+      return (T)symbol.CreateTreeNode();
+    }
+    #endregion
+
+    #region tree simplification
+    // these simplification methods rely on the assumption that child nodes of the current node have already been simplified
+    // (in other words simplification should be applied in a bottom-up fashion) 
+    public static ISymbolicExpressionTree Simplify(ISymbolicExpressionTree tree) {
+      ulong hashFunction(byte[] bytes) => HashUtil.JSHash(bytes);
+      var root = tree.Root.GetSubtree(0).GetSubtree(0);
+      var nodes = root.MakeNodes();
+      var simplified = nodes.Simplify(hashFunction);
+      return simplified.ToTree();
+    }
+
+    public static void SimplifyAddition(ref HashNode<ISymbolicExpressionTreeNode>[] nodes, int i) {
+      // simplify additions of terms by eliminating terms with the same symbol and hash
+      var children = nodes.IterateChildren(i);
+
+      // we always assume the child nodes are sorted
+      var curr = children[0];
+      var node = nodes[i];
+
+      foreach (var j in children.Skip(1)) {
+        if (nodes[j] == nodes[curr]) {
+          nodes.SetEnabled(j, false);
+          node.Arity--;
+        } else {
+          curr = j;
+        }
+      }
+      if (node.Arity == 1) { // if the arity is 1 we don't need the addition node at all
+        node.Enabled = false;
+      }
+    }
+
+    // simplify multiplications by reducing constants and div terms  
+    public static void SimplifyMultiplication(ref HashNode<ISymbolicExpressionTreeNode>[] nodes, int i) {
+      var node = nodes[i];
+      var children = nodes.IterateChildren(i);
+
+      for (int j = 0; j < children.Length; ++j) {
+        var c = children[j];
+        var child = nodes[c];
+
+        if (!child.Enabled)
+          continue;
+
+        var symbol = child.Data.Symbol;
+        if (symbol is Constant) {
+          for (int k = j + 1; k < children.Length; ++k) {
+            var d = children[k];
+            if (nodes[d].Data.Symbol is Constant) {
+              nodes[d].Enabled = false;
+              node.Arity--;
+            } else {
+              break;
+            }
+          }
+        } else if (symbol is Division) {
+          var div = nodes[c];
+          var denominator =
+            div.Arity == 1 ?
+            nodes[c - 1] :                    // 1 / x is expressed as div(x) (with a single child)
+            nodes[c - nodes[c - 1].Size - 2]; // assume division always has arity 1 or 2
+
+          foreach (var d in children) {
+            if (nodes[d].Enabled && nodes[d] == denominator) {
+              nodes[c].Enabled = nodes[d].Enabled = denominator.Enabled = false;
+              node.Arity -= 2; // matching child + division node
+              break;
+            }
+          }
+        }
+
+        if (node.Arity == 0) { // if everything is simplified this node becomes constant
+          var constantTreeNode = constant.CreateTreeNode<ConstantTreeNode>();
+          constantTreeNode.Value = 1;
+          nodes[i] = constantTreeNode.ToHashNode();
+        } else if (node.Arity == 1) { // when i have only 1 arg left i can skip this node
+          node.Enabled = false;
+        }
+      }
+    }
+
+    public static void SimplifyDivision(ref HashNode<ISymbolicExpressionTreeNode>[] nodes, int i) {
+      var node = nodes[i];
+      var children = nodes.IterateChildren(i);
+
+      var tmp = nodes;
+
+      if (children.All(x => tmp[x].Data.Symbol is Constant)) {
+        var v = ((ConstantTreeNode)nodes[children.First()].Data).Value;
+        if (node.Arity == 1) {
+          v = 1 / v;
+        } else if (node.Arity > 1) {
+          foreach (var j in children.Skip(1)) {
+            v /= ((ConstantTreeNode)nodes[j].Data).Value;
+          }
+        }
+        var constantTreeNode = constant.CreateTreeNode<ConstantTreeNode>();
+        constantTreeNode.Value = v;
+        nodes[i] = constantTreeNode.ToHashNode();
+        return;
+      }
+
+      var nominator = nodes[children[0]];
+      foreach (var j in children.Skip(1)) {
+        var denominator = nodes[j];
+        if (nominator == denominator) {
+          // disable all the children of the division node (nominator and children + denominator and children)
+          nominator.Enabled = denominator.Enabled = false;
+          node.Arity -= 2; // nominator + denominator
+        }
+        if (node.Arity == 0) {
+          var constantTreeNode = constant.CreateTreeNode<ConstantTreeNode>();
+          constantTreeNode.Value = 1; // x / x = 1
+          nodes[i] = constantTreeNode.ToHashNode();
+        }
+      }
+    }
+
+    public static void SimplifyUnaryNode(ref HashNode<ISymbolicExpressionTreeNode>[] nodes, int i) {
+      // check if the child of the unary node is a constant, then the whole node can be simplified
+      var parent = nodes[i];
+      var child = nodes[i - 1];
+
+      var parentSymbol = parent.Data.Symbol;
+      var childSymbol = child.Data.Symbol;
+
+      if (childSymbol is Constant) {
+        nodes[i].Enabled = false;
+      } else if ((parentSymbol is Exponential && childSymbol is Logarithm) || (parentSymbol is Logarithm && childSymbol is Exponential)) {
+        child.Enabled = parent.Enabled = false;
+      }
+    }
+
+    public static void SimplifyBinaryNode(ref HashNode<ISymbolicExpressionTreeNode>[] nodes, int i) {
+      var children = nodes.IterateChildren(i);
+      var tmp = nodes;
+      if (children.All(x => tmp[x].Data.Symbol is Constant)) {
+        foreach (var j in children) {
+          nodes[j].Enabled = false;
+        }
+        nodes[i] = constant.CreateTreeNode().ToHashNode();
+      }
+    }
+    #endregion
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/HeuristicLab.Problems.DataAnalysis.Symbolic-3.4.csproj
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/HeuristicLab.Problems.DataAnalysis.Symbolic-3.4.csproj	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/HeuristicLab.Problems.DataAnalysis.Symbolic-3.4.csproj	(revision 16337)
@@ -0,0 +1,418 @@
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+      <HintPath>..\..\bin\AutoDiff-1.0.dll</HintPath>
+      <Private>False</Private>
+    </Reference>
+    <Reference Include="HeuristicLab.Problems.DataAnalysis.Symbolic.NativeInterpreter-0.1, Version=0.0.0.1, Culture=neutral, PublicKeyToken=ba48961d6f65dcec, processorArchitecture=MSIL">
+      <SpecificVersion>False</SpecificVersion>
+      <HintPath>..\..\bin\HeuristicLab.Problems.DataAnalysis.Symbolic.NativeInterpreter-0.1.dll</HintPath>
+      <Private>False</Private>
+    </Reference>
+    <Reference Include="System" />
+    <Reference Include="System.Core">
+      <RequiredTargetFramework>3.5</RequiredTargetFramework>
+    </Reference>
+    <Reference Include="System.Drawing" />
+    <Reference Include="System.Xml.Linq">
+      <RequiredTargetFramework>3.5</RequiredTargetFramework>
+    </Reference>
+    <Reference Include="System.Data.DataSetExtensions">
+      <RequiredTargetFramework>3.5</RequiredTargetFramework>
+    </Reference>
+    <Reference Include="System.Data" />
+    <Reference Include="System.Xml" />
+  </ItemGroup>
+  <ItemGroup>
+    <Compile Include="Analyzers\SymbolicDataAnalysisBottomUpDiversityAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisBuildingBlockAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisSingleObjectivePruningAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisSingleObjectiveValidationParetoBestSolutionAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisSingleObjectiveTrainingParetoBestSolutionAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisMultiObjectiveValidationAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisMultiObjectiveValidationBestSolutionAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisSingleObjectiveValidationAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisSingleObjectiveValidationBestSolutionAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisMultiObjectiveAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisSingleObjectiveAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisMultiObjectiveTrainingBestSolutionAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisSingleObjectiveTrainingBestSolutionAnalyzer.cs">
+      <SubType>Code</SubType>
+    </Compile>
+    <Compile Include="Converters\LinearModelToTreeConverter.cs" />
+    <Compile Include="Converters\TreeSimplifier.cs" />
+    <Compile Include="Converters\DerivativeCalculator.cs" />
+    <Compile Include="Converters\TreeToAutoDiffTermConverter.cs" />
+    <Compile Include="Crossovers\SymbolicDataAnalysisExpressionDiversityPreservingCrossover.cs" />
+    <Compile Include="Formatters\InfixExpressionFormatter.cs" />
+    <Compile Include="Formatters\TSQLExpressionFormatter.cs" />
+    <Compile Include="Formatters\SymbolicDataAnalysisExpressionMathematicaFormatter.cs" />
+    <Compile Include="Formatters\SymbolicDataAnalysisExpressionCSharpFormatter.cs" />
+    <Compile Include="Hashing\HashExtensions.cs" />
+    <Compile Include="Hashing\HashUtil.cs" />
+    <Compile Include="Hashing\SymbolicExpressionTreeHash.cs" />
+    <Compile Include="Importer\InfixExpressionParser.cs" />
+    <Compile Include="Importer\SymbolicExpressionImporter.cs" />
+    <Compile Include="Importer\Token.cs" />
+    <Compile Include="Interfaces\IModelBacktransformator.cs" />
+    <Compile Include="Interfaces\IVariableTreeNode.cs" />
+    <Compile Include="Interfaces\IVariableSymbol.cs" />
+    <Compile Include="Interpreter\BatchInstruction.cs" />
+    <Compile Include="Interpreter\BatchOperations.cs" />
+    <Compile Include="Interpreter\SymbolicDataAnalysisExpressionCompiledTreeInterpreter.cs" />
+    <Compile Include="Interpreter\SymbolicDataAnalysisExpressionTreeBatchInterpreter.cs" />
+    <Compile Include="Interpreter\SymbolicDataAnalysisExpressionTreeNativeInterpreter.cs" />
+    <Compile Include="SymbolicDataAnalysisExpressionTreeSimplificationOperator.cs" />
+    <Compile Include="SymbolicDataAnalysisModelComplexityCalculator.cs" />
+    <Compile Include="SymbolicDataAnalysisExpressionPruningOperator.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisVariableFrequencyAnalyzer.cs" />
+    <Compile Include="Analyzers\SymbolicDataAnalysisAlleleFrequencyAnalyzer.cs" />
+    <Compile Include="Creators\MultiSymbolicDataAnalysisExpressionCreator.cs" />
+    <Compile Include="Creators\SymbolicDataAnalysisExpressionFullTreeCreator.cs" />
+    <Compile Include="Creators\SymbolicDataAnalysisExpressionGrowTreeCreator.cs" />
+    <Compile Include="Creators\SymbolicDataAnalysisExpressionRampedHalfAndHalfTreeCreator.cs" />
+    <Compile Include="Creators\SymbolicDataAnalysisExpressionTreeCreator.cs" />
+    <Compile Include="Crossovers\MultiSymbolicDataAnalysisExpressionCrossover.cs" />
+    <Compile Include="Crossovers\SymbolicDataAnalysisExpressionContextAwareCrossover.cs" />
+    <Compile Include="Crossovers\SymbolicDataAnalysisExpressionCrossover.cs" />
+    <Compile Include="Crossovers\SymbolicDataAnalysisExpressionDepthConstrainedCrossover.cs" />
+    <Compile Include="Crossovers\SymbolicDataAnalysisExpressionDeterministicBestCrossover.cs" />
+    <Compile Include="Crossovers\SymbolicDataAnalysisExpressionProbabilisticFunctionalCrossover.cs" />
+    <Compile Include="Crossovers\SymbolicDataAnalysisExpressionSemanticSimilarityCrossover.cs" />
+    <Compile Include="Formatters\SymbolicDataAnalysisExpressionExcelFormatter.cs" />
+    <Compile Include="Formatters\SymbolicDataAnalysisExpressionSmalltalkFormatter.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisExpressionCrossover.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisImpactValuesCalculator.cs" />
+    <Compile Include="Interpreter\InterpreterState.cs" />
+    <Compile Include="Interpreter\OpCodes.cs" />
+    <Compile Include="Interpreter\SymbolicDataAnalysisExpressionTreeILEmittingInterpreter.cs" />
+    <Compile Include="Interpreter\SymbolicDataAnalysisExpressionTreeInterpreter.cs" />
+    <Compile Include="Interpreter\SymbolicDataAnalysisExpressionTreeLinearInterpreter.cs" />
+    <Compile Include="Plugin.cs" />
+    <Compile Include="Formatters\SymbolicDataAnalysisExpressionLatexFormatter.cs" />
+    <Compile Include="Formatters\SymbolicDataAnalysisExpressionMATLABFormatter.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisBoundedOperator.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisExpressionTreeInterpreter.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisProblem.cs" />
+    <Compile Include="SymbolicDataAnalysisModel.cs">
+      <SubType>Code</SubType>
+    </Compile>
+    <Compile Include="SymbolicDataAnalysisMultiObjectiveProblem.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisValidationAnalyzer.cs" />
+    <Compile Include="Grammars\ArithmeticExpressionGrammar.cs" />
+    <Compile Include="Grammars\FullFunctionalExpressionGrammar.cs" />
+    <Compile Include="Grammars\TypeCoherentExpressionGrammar.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisMultiObjectiveAnalyzer.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisSingleObjectiveAnalyzer.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisAnalyzer.cs" />
+    <Compile Include="SymbolicDataAnalysisSingleObjectiveProblem.cs" />
+    <Compile Include="SymbolicDataAnalysisProblem.cs" />
+    <Compile Include="SymbolicDataAnalysisSolutionImpactValuesCalculator.cs" />
+    <Compile Include="Symbols\Addition.cs" />
+    <Compile Include="Symbols\And.cs" />
+    <Compile Include="Symbols\AutoregressiveVariable.cs" />
+    <Compile Include="Symbols\Average.cs" />
+    <Compile Include="Symbols\Constant.cs" />
+    <Compile Include="Symbols\ConstantTreeNode.cs" />
+    <Compile Include="Symbols\AiryA.cs" />
+    <Compile Include="Symbols\AiryB.cs" />
+    <Compile Include="Symbols\Bessel.cs" />
+    <Compile Include="Symbols\BinaryFactorVariable.cs" />
+    <Compile Include="Symbols\BinaryFactorVariableTreeNode.cs" />
+    <Compile Include="Symbols\FactorVariableTreeNode.cs" />
+    <Compile Include="Symbols\FactorVariable.cs" />
+    <Compile Include="Symbols\VariableBase.cs" />
+    <Compile Include="Symbols\VariableTreeNodeBase.cs" />
+    <Compile Include="Symbols\Xor.cs" />
+    <Compile Include="Symbols\Erf.cs" />
+    <Compile Include="Symbols\Norm.cs" />
+    <Compile Include="Symbols\FresnelCosineIntegral.cs" />
+    <Compile Include="Symbols\FresnelSineIntegral.cs" />
+    <Compile Include="Symbols\HyperbolicSineIntegral.cs" />
+    <Compile Include="Symbols\HyperbolicCosineIntegral.cs" />
+    <Compile Include="Symbols\SineIntegral.cs" />
+    <Compile Include="Symbols\CosineIntegral.cs" />
+    <Compile Include="Symbols\ExponentialIntegralEi.cs" />
+    <Compile Include="Symbols\Dawson.cs" />
+    <Compile Include="Symbols\Psi.cs" />
+    <Compile Include="Symbols\Gamma.cs" />
+    <Compile Include="Symbols\SquareRoot.cs" />
+    <Compile Include="Symbols\Square.cs" />
+    <Compile Include="Symbols\Cosine.cs" />
+    <Compile Include="Symbols\Derivative.cs" />
+    <Compile Include="Symbols\Division.cs" />
+    <Compile Include="Symbols\Exponential.cs" />
+    <Compile Include="Symbols\GreaterThan.cs" />
+    <Compile Include="Symbols\IfThenElse.cs" />
+    <Compile Include="Symbols\ILaggedTreeNode.cs" />
+    <Compile Include="Symbols\Integral.cs" />
+    <Compile Include="Symbols\LaggedSymbol.cs" />
+    <Compile Include="Symbols\LaggedTreeNode.cs" />
+    <Compile Include="Symbols\LaggedVariable.cs" />
+    <Compile Include="Symbols\LaggedVariableTreeNode.cs" />
+    <Compile Include="Symbols\LessThan.cs" />
+    <Compile Include="Symbols\Logarithm.cs" />
+    <Compile Include="Symbols\Multiplication.cs" />
+    <Compile Include="Symbols\Not.cs" />
+    <Compile Include="Symbols\Or.cs" />
+    <Compile Include="Symbols\Power.cs" />
+    <Compile Include="Symbols\Root.cs" />
+    <Compile Include="Symbols\Sine.cs" />
+    <Compile Include="Symbols\Subtraction.cs" />
+    <Compile Include="Symbols\Tangent.cs" />
+    <Compile Include="Symbols\TimeLag.cs" />
+    <Compile Include="Symbols\Variable.cs" />
+    <Compile Include="Symbols\VariableCondition.cs" />
+    <Compile Include="Symbols\VariableConditionTreeNode.cs" />
+    <Compile Include="Symbols\VariableTreeNode.cs" />
+    <Compile Include="Transformations\SymbolicExpressionTreeBacktransformator.cs" />
+    <Compile Include="Transformations\TransformationToSymbolicTreeMapper.cs" />
+    <Compile Include="TreeMatching\SymbolicExpressionTreeBottomUpSimilarityCalculator.cs" />
+    <Compile Include="TreeMatching\SymbolicExpressionTreeCanonicalSorter.cs" />
+    <Compile Include="TreeMatching\SymbolicExpressionTreeEqualityComparer.cs" />
+    <Compile Include="TreeMatching\SymbolicExpressionTreeMatching.cs" />
+    <Compile Include="TreeMatching\SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator.cs" />
+    <Compile Include="TreeMatching\SymbolicExpressionTreeNodeComparer.cs" />
+    <Compile Include="TreeMatching\SymbolicExpressionTreeNodeEqualityComparer.cs" />
+    <Compile Include="TreeMatching\SymbolicExpressionTreePhenotypicSimilarityCalculator.cs" />
+    <None Include="HeuristicLab.snk" />
+    <None Include="Plugin.cs.frame" />
+    <None Include="Properties\AssemblyInfo.cs.frame" />
+    <Compile Include="Evaluators\SymbolicDataAnalysisMultiObjectiveEvaluator.cs" />
+    <Compile Include="Evaluators\SymbolicDataAnalysisSingleObjectiveEvaluator.cs" />
+    <Compile Include="Evaluators\SymbolicDataAnalysisEvaluator.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisInterpreterOperator.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisMultiObjectiveEvaluator.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisEvaluator.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisGrammar.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisModel.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisSingleObjectiveEvaluator.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisSolution.cs" />
+    <Compile Include="Interfaces\ISymbolicDataAnalysisSolutionCreator.cs" />
+    <Compile Include="Properties\AssemblyInfo.cs" />
+  </ItemGroup>
+  <ItemGroup>
+    <BootstrapperPackage Include="Microsoft.Net.Client.3.5">
+      <Visible>False</Visible>
+      <ProductName>.NET Framework 3.5 SP1 Client Profile</ProductName>
+      <Install>false</Install>
+    </BootstrapperPackage>
+    <BootstrapperPackage Include="Microsoft.Net.Framework.3.5.SP1">
+      <Visible>False</Visible>
+      <ProductName>.NET Framework 3.5 SP1</ProductName>
+      <Install>true</Install>
+    </BootstrapperPackage>
+    <BootstrapperPackage Include="Microsoft.Windows.Installer.3.1">
+      <Visible>False</Visible>
+      <ProductName>Windows Installer 3.1</ProductName>
+      <Install>true</Install>
+    </BootstrapperPackage>
+  </ItemGroup>
+  <ItemGroup>
+    <ProjectReference Include="..\..\HeuristicLab.Analysis\3.3\HeuristicLab.Analysis-3.3.csproj">
+      <Project>{887425B4-4348-49ED-A457-B7D2C26DDBF9}</Project>
+      <Name>HeuristicLab.Analysis-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Collections\3.3\HeuristicLab.Collections-3.3.csproj">
+      <Project>{958B43BC-CC5C-4FA2-8628-2B3B01D890B6}</Project>
+      <Name>HeuristicLab.Collections-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Common.Resources\3.3\HeuristicLab.Common.Resources-3.3.csproj">
+      <Project>{0E27A536-1C4A-4624-A65E-DC4F4F23E3E1}</Project>
+      <Name>HeuristicLab.Common.Resources-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Common\3.3\HeuristicLab.Common-3.3.csproj">
+      <Project>{A9AD58B9-3EF9-4CC1-97E5-8D909039FF5C}</Project>
+      <Name>HeuristicLab.Common-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Core\3.3\HeuristicLab.Core-3.3.csproj">
+      <Project>{C36BD924-A541-4A00-AFA8-41701378DDC5}</Project>
+      <Name>HeuristicLab.Core-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Data\3.3\HeuristicLab.Data-3.3.csproj">
+      <Project>{BBAB9DF5-5EF3-4BA8-ADE9-B36E82114937}</Project>
+      <Name>HeuristicLab.Data-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Encodings.SymbolicExpressionTreeEncoding\3.4\HeuristicLab.Encodings.SymbolicExpressionTreeEncoding-3.4.csproj">
+      <Project>{06D4A186-9319-48A0-BADE-A2058D462EEA}</Project>
+      <Name>HeuristicLab.Encodings.SymbolicExpressionTreeEncoding-3.4</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Operators\3.3\HeuristicLab.Operators-3.3.csproj">
+      <Project>{23DA7FF4-D5B8-41B6-AA96-F0561D24F3EE}</Project>
+      <Name>HeuristicLab.Operators-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Optimization.Operators\3.3\HeuristicLab.Optimization.Operators-3.3.csproj">
+      <Project>{25087811-F74C-4128-BC86-8324271DA13E}</Project>
+      <Name>HeuristicLab.Optimization.Operators-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Optimization\3.3\HeuristicLab.Optimization-3.3.csproj">
+      <Project>{14AB8D24-25BC-400C-A846-4627AA945192}</Project>
+      <Name>HeuristicLab.Optimization-3.3</Name>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Parameters\3.3\HeuristicLab.Parameters-3.3.csproj">
+      <Project>{56F9106A-079F-4C61-92F6-86A84C2D84B7}</Project>
+      <Name>HeuristicLab.Parameters-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Persistence\3.3\HeuristicLab.Persistence-3.3.csproj">
+      <Project>{102BC7D3-0EF9-439C-8F6D-96FF0FDB8E1B}</Project>
+      <Name>HeuristicLab.Persistence-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.PluginInfrastructure\3.3\HeuristicLab.PluginInfrastructure-3.3.csproj">
+      <Project>{94186A6A-5176-4402-AE83-886557B53CCA}</Project>
+      <Name>HeuristicLab.PluginInfrastructure-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Problems.DataAnalysis\3.4\HeuristicLab.Problems.DataAnalysis-3.4.csproj">
+      <Project>{DF87C13E-A889-46FF-8153-66DCAA8C5674}</Project>
+      <Name>HeuristicLab.Problems.DataAnalysis-3.4</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Problems.Instances\3.3\HeuristicLab.Problems.Instances-3.3.csproj">
+      <Project>{3540E29E-4793-49E7-8EE2-FEA7F61C3994}</Project>
+      <Name>HeuristicLab.Problems.Instances-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+    <ProjectReference Include="..\..\HeuristicLab.Random\3.3\HeuristicLab.Random-3.3.csproj">
+      <Project>{F4539FB6-4708-40C9-BE64-0A1390AEA197}</Project>
+      <Name>HeuristicLab.Random-3.3</Name>
+      <Private>False</Private>
+    </ProjectReference>
+  </ItemGroup>
+  <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
+  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
+       Other similar extension points exist, see Microsoft.Common.targets.
+  <Target Name="BeforeBuild">
+  </Target>
+  <Target Name="AfterBuild">
+  </Target>
+  -->
+  <PropertyGroup>
+    <PreBuildEvent Condition=" '$(OS)' == 'Windows_NT' ">set Path=%25Path%25;$(ProjectDir);$(SolutionDir)
+set ProjectDir=$(ProjectDir)
+set SolutionDir=$(SolutionDir)
+set Outdir=$(Outdir)
+
+call PreBuildEvent.cmd
+</PreBuildEvent>
+    <PreBuildEvent Condition=" '$(OS)' != 'Windows_NT' ">
+export ProjectDir=$(ProjectDir)
+export SolutionDir=$(SolutionDir)
+
+$SolutionDir/PreBuildEvent.sh
+</PreBuildEvent>
+  </PropertyGroup>
+</Project>
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/InfixExpressionParser.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/InfixExpressionParser.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/InfixExpressionParser.cs	(revision 16337)
@@ -0,0 +1,505 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using HeuristicLab.Collections;
+using HeuristicLab.Common;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Parses mathematical expressions in infix form. E.g. x1 * (3.0 * x2 + x3)
+  /// Identifier format (functions or variables): '_' | letter { '_' | letter | digit }
+  /// Variables names and variable values can be set under quotes "" or '' because variable names might contain spaces. 
+  ///   Variable = ident | " ident " | ' ident ' 
+  /// It is also possible to use functions e.g. log("x1") or real-valued constants e.g. 3.1415 . 
+  /// Variable names are case sensitive. Function names are not case sensitive.
+  /// 
+  /// 
+  /// S             = Expr EOF
+  /// Expr          = ['-' | '+'] Term { '+' Term | '-' Term }
+  /// Term          = Fact { '*' Fact | '/' Fact }
+  /// Fact          = '(' Expr ')' 
+  ///                 | 'LAG' '(' varId ',' ['+' | '-' ] number ')' 
+  ///                 | funcId '(' ArgList ')' 
+  ///                 | VarExpr | number
+  /// ArgList       = Expr { ',' Expr }
+  /// VarExpr       = varId OptFactorPart
+  /// OptFactorPart = [ ('=' varVal | '[' ['+' | '-' ] number {',' ['+' | '-' ] number } ']' ) ]
+  /// varId         =  ident | ' ident ' | " ident "
+  /// varVal        =  ident | ' ident ' | " ident "
+  /// ident         =  '_' | letter { '_' | letter | digit }
+  /// </summary>
+  public sealed class InfixExpressionParser {
+    private enum TokenType { Operator, Identifier, Number, LeftPar, RightPar, LeftBracket, RightBracket, Comma, Eq, End, NA };
+    private class Token {
+      internal double doubleVal;
+      internal string strVal;
+      internal TokenType TokenType;
+    }
+
+    private class SymbolNameComparer : IEqualityComparer<ISymbol>, IComparer<ISymbol> {
+      public int Compare(ISymbol x, ISymbol y) {
+        return x.Name.CompareTo(y.Name);
+      }
+
+      public bool Equals(ISymbol x, ISymbol y) {
+        return Compare(x, y) == 0;
+      }
+
+      public int GetHashCode(ISymbol obj) {
+        return obj.Name.GetHashCode();
+      }
+    }
+    // format name <-> symbol 
+    // the lookup table is also used in the corresponding formatter
+    internal static readonly BidirectionalLookup<string, ISymbol>
+      knownSymbols = new BidirectionalLookup<string, ISymbol>(StringComparer.InvariantCulture, new SymbolNameComparer());
+
+    private Constant constant = new Constant();
+    private Variable variable = new Variable();
+    private BinaryFactorVariable binaryFactorVar = new BinaryFactorVariable();
+    private FactorVariable factorVar = new FactorVariable();
+
+    private ProgramRootSymbol programRootSymbol = new ProgramRootSymbol();
+    private StartSymbol startSymbol = new StartSymbol();
+
+    static InfixExpressionParser() {
+      // populate bidirectional lookup
+      var dict = new Dictionary<string, ISymbol>
+      {
+        { "+", new Addition()},
+        { "/", new Division()},
+        { "*", new Multiplication()},
+        { "-", new Subtraction()},
+        { "EXP", new Exponential()},
+        { "LOG", new Logarithm()},
+        { "POW", new Power()},
+        { "ROOT", new Root()},
+        { "SQR", new Square() },
+        { "SQRT", new SquareRoot() },
+        { "SIN",new Sine()},
+        { "COS", new Cosine()},
+        { "TAN", new Tangent()},
+        { "AIRYA", new AiryA()},
+        { "AIRYB", new AiryB()},
+        { "BESSEL", new Bessel()},
+        { "COSINT", new CosineIntegral()},
+        { "SININT", new SineIntegral()},
+        { "HYPCOSINT", new HyperbolicCosineIntegral()},
+        { "HYPSININT", new HyperbolicSineIntegral()},
+        { "FRESNELSININT", new FresnelSineIntegral()},
+        { "FRESNELCOSINT", new FresnelCosineIntegral()},
+        { "NORM", new Norm()},
+        { "ERF", new Erf()},
+        { "GAMMA", new Gamma()},
+        { "PSI", new Psi()},
+        { "DAWSON", new Dawson()},
+        { "EXPINT", new ExponentialIntegralEi()},
+        { "MEAN", new Average()},
+        { "IF", new IfThenElse()},
+        { "GT", new GreaterThan()},
+        { "LT", new LessThan()},
+        { "AND", new And()},
+        { "OR", new Or()},
+        { "NOT", new Not()},
+        { "XOR", new Xor()},
+        { "DIFF", new Derivative()},
+        { "LAG", new LaggedVariable() },
+      };
+
+
+      foreach (var kvp in dict) {
+        knownSymbols.Add(kvp.Key, kvp.Value);
+      }
+    }
+
+    public ISymbolicExpressionTree Parse(string str) {
+      ISymbolicExpressionTreeNode root = programRootSymbol.CreateTreeNode();
+      ISymbolicExpressionTreeNode start = startSymbol.CreateTreeNode();
+      var allTokens = GetAllTokens(str).ToArray();
+      ISymbolicExpressionTreeNode mainBranch = ParseS(new Queue<Token>(allTokens));
+
+      // only a main branch was given => insert the main branch into the default tree template
+      root.AddSubtree(start);
+      start.AddSubtree(mainBranch);
+      return new SymbolicExpressionTree(root);
+    }
+
+    private IEnumerable<Token> GetAllTokens(string str) {
+      int pos = 0;
+      while (true) {
+        while (pos < str.Length && Char.IsWhiteSpace(str[pos])) pos++;
+        if (pos >= str.Length) {
+          yield return new Token { TokenType = TokenType.End, strVal = "" };
+          yield break;
+        }
+        if (char.IsDigit(str[pos])) {
+          // read number (=> read until white space or operator or comma)
+          var sb = new StringBuilder();
+          sb.Append(str[pos]);
+          pos++;
+          while (pos < str.Length && !char.IsWhiteSpace(str[pos])
+            && (str[pos] != '+' || str[pos - 1] == 'e' || str[pos - 1] == 'E')     // continue reading exponents
+            && (str[pos] != '-' || str[pos - 1] == 'e' || str[pos - 1] == 'E')
+            && str[pos] != '*'
+            && str[pos] != '/'
+            && str[pos] != ')'
+            && str[pos] != ']'
+            && str[pos] != ',') {
+            sb.Append(str[pos]);
+            pos++;
+          }
+          double dblVal;
+          if (double.TryParse(sb.ToString(), NumberStyles.Float, CultureInfo.InvariantCulture, out dblVal))
+            yield return new Token { TokenType = TokenType.Number, strVal = sb.ToString(), doubleVal = dblVal };
+          else yield return new Token { TokenType = TokenType.NA, strVal = sb.ToString() };
+        } else if (char.IsLetter(str[pos]) || str[pos] == '_') {
+          // read ident
+          var sb = new StringBuilder();
+          sb.Append(str[pos]);
+          pos++;
+          while (pos < str.Length &&
+            (char.IsLetter(str[pos]) || str[pos] == '_' || char.IsDigit(str[pos]))) {
+            sb.Append(str[pos]);
+            pos++;
+          }
+          yield return new Token { TokenType = TokenType.Identifier, strVal = sb.ToString() };
+        } else if (str[pos] == '"') {
+          // read to next " 
+          pos++;
+          var sb = new StringBuilder();
+          while (pos < str.Length && str[pos] != '"') {
+            sb.Append(str[pos]);
+            pos++;
+          }
+          if (pos < str.Length && str[pos] == '"') {
+            pos++; // skip "
+            yield return new Token { TokenType = TokenType.Identifier, strVal = sb.ToString() };
+          } else
+            yield return new Token { TokenType = TokenType.NA };
+
+        } else if (str[pos] == '\'') {
+          // read to next '
+          pos++;
+          var sb = new StringBuilder();
+          while (pos < str.Length && str[pos] != '\'') {
+            sb.Append(str[pos]);
+            pos++;
+          }
+          if (pos < str.Length && str[pos] == '\'') {
+            pos++; // skip '
+            yield return new Token { TokenType = TokenType.Identifier, strVal = sb.ToString() };
+          } else
+            yield return new Token { TokenType = TokenType.NA };
+        } else if (str[pos] == '+') {
+          pos++;
+          yield return new Token { TokenType = TokenType.Operator, strVal = "+" };
+        } else if (str[pos] == '-') {
+          pos++;
+          yield return new Token { TokenType = TokenType.Operator, strVal = "-" };
+        } else if (str[pos] == '/') {
+          pos++;
+          yield return new Token { TokenType = TokenType.Operator, strVal = "/" };
+        } else if (str[pos] == '*') {
+          pos++;
+          yield return new Token { TokenType = TokenType.Operator, strVal = "*" };
+        } else if (str[pos] == '(') {
+          pos++;
+          yield return new Token { TokenType = TokenType.LeftPar, strVal = "(" };
+        } else if (str[pos] == ')') {
+          pos++;
+          yield return new Token { TokenType = TokenType.RightPar, strVal = ")" };
+        } else if (str[pos] == '[') {
+          pos++;
+          yield return new Token { TokenType = TokenType.LeftBracket, strVal = "[" };
+        } else if (str[pos] == ']') {
+          pos++;
+          yield return new Token { TokenType = TokenType.RightBracket, strVal = "]" };
+        } else if (str[pos] == '=') {
+          pos++;
+          yield return new Token { TokenType = TokenType.Eq, strVal = "=" };
+        } else if (str[pos] == ',') {
+          pos++;
+          yield return new Token { TokenType = TokenType.Comma, strVal = "," };
+        } else {
+          throw new ArgumentException("Invalid character: " + str[pos]);
+        }
+      }
+    }
+    /// S             = Expr EOF
+    private ISymbolicExpressionTreeNode ParseS(Queue<Token> tokens) {
+      var expr = ParseExpr(tokens);
+
+      var endTok = tokens.Dequeue();
+      if (endTok.TokenType != TokenType.End)
+        throw new ArgumentException(string.Format("Expected end of expression (got {0})", endTok.strVal));
+
+      return expr;
+    }
+
+    /// Expr          = ['-' | '+'] Term { '+' Term | '-' Term }
+    private ISymbolicExpressionTreeNode ParseExpr(Queue<Token> tokens) {
+      var next = tokens.Peek();
+      var posTerms = new List<ISymbolicExpressionTreeNode>();
+      var negTerms = new List<ISymbolicExpressionTreeNode>();
+      bool negateFirstTerm = false;
+      if (next.TokenType == TokenType.Operator && (next.strVal == "+" || next.strVal == "-")) {
+        tokens.Dequeue();
+        if (next.strVal == "-")
+          negateFirstTerm = true;
+      }
+      var t = ParseTerm(tokens);
+      if (negateFirstTerm) negTerms.Add(t);
+      else posTerms.Add(t);
+
+      next = tokens.Peek();
+      while (next.strVal == "+" || next.strVal == "-") {
+        switch (next.strVal) {
+          case "+": {
+              tokens.Dequeue();
+              var term = ParseTerm(tokens);
+              posTerms.Add(term);
+              break;
+            }
+          case "-": {
+              tokens.Dequeue();
+              var term = ParseTerm(tokens);
+              negTerms.Add(term);
+              break;
+            }
+        }
+        next = tokens.Peek();
+      }
+
+      var sum = GetSymbol("+").CreateTreeNode();
+      foreach (var posTerm in posTerms) sum.AddSubtree(posTerm);
+      if (negTerms.Any()) {
+        if (negTerms.Count == 1) {
+          var sub = GetSymbol("-").CreateTreeNode();
+          sub.AddSubtree(negTerms.Single());
+          sum.AddSubtree(sub);
+        } else {
+          var sumNeg = GetSymbol("+").CreateTreeNode();
+          foreach (var negTerm in negTerms) sumNeg.AddSubtree(negTerm);
+
+          var constNode = (ConstantTreeNode)constant.CreateTreeNode();
+          constNode.Value = -1.0;
+          var prod = GetSymbol("*").CreateTreeNode();
+          prod.AddSubtree(constNode);
+          prod.AddSubtree(sumNeg);
+
+          sum.AddSubtree(prod);
+        }
+      }
+      if (sum.SubtreeCount == 1) return sum.Subtrees.First();
+      else return sum;
+    }
+
+    private ISymbol GetSymbol(string tok) {
+      var symb = knownSymbols.GetByFirst(tok).FirstOrDefault();
+      if (symb == null) throw new ArgumentException(string.Format("Unknown token {0} found.", tok));
+      return symb;
+    }
+
+    /// Term          = Fact { '*' Fact | '/' Fact }
+    private ISymbolicExpressionTreeNode ParseTerm(Queue<Token> tokens) {
+      var factors = new List<ISymbolicExpressionTreeNode>();
+      var firstFactor = ParseFact(tokens);
+      factors.Add(firstFactor);
+
+      var next = tokens.Peek();
+      while (next.strVal == "*" || next.strVal == "/") {
+        switch (next.strVal) {
+          case "*": {
+              tokens.Dequeue();
+              var fact = ParseFact(tokens);
+              factors.Add(fact);
+              break;
+            }
+          case "/": {
+              tokens.Dequeue();
+              var invFact = ParseFact(tokens);
+              var divNode = GetSymbol("/").CreateTreeNode(); // 1/x
+              divNode.AddSubtree(invFact);
+              factors.Add(divNode);
+              break;
+            }
+        }
+
+        next = tokens.Peek();
+      }
+      if (factors.Count == 1) return factors.First();
+      else {
+        var prod = GetSymbol("*").CreateTreeNode();
+        foreach (var f in factors) prod.AddSubtree(f);
+        return prod;
+      }
+    }
+
+    /// Fact          = '(' Expr ')' 
+    ///                 | 'LAG' '(' varId ',' ['+' | '-' ] number ')' 
+    ///                 | funcId '(' ArgList ')' 
+    ///                 | VarExpr | number
+    /// ArgList       = Expr { ',' Expr }
+    /// VarExpr       = varId OptFactorPart
+    /// OptFactorPart = [ ('=' varVal | '[' ['+' | '-' ] number {',' ['+' | '-' ] number } ']' ) ]
+    /// varId         =  ident | ' ident ' | " ident "
+    /// varVal        =  ident | ' ident ' | " ident "
+    /// ident         =  '_' | letter { '_' | letter | digit }
+    private ISymbolicExpressionTreeNode ParseFact(Queue<Token> tokens) {
+      var next = tokens.Peek();
+      if (next.TokenType == TokenType.LeftPar) {
+        tokens.Dequeue();
+        var expr = ParseExpr(tokens);
+        var rPar = tokens.Dequeue();
+        if (rPar.TokenType != TokenType.RightPar)
+          throw new ArgumentException("expected )");
+        return expr;
+      } else if (next.TokenType == TokenType.Identifier) {
+        var idTok = tokens.Dequeue();
+        if (tokens.Peek().TokenType == TokenType.LeftPar) {
+          // function identifier or LAG
+          var funcId = idTok.strVal.ToUpperInvariant();
+
+          var funcNode = GetSymbol(funcId).CreateTreeNode();
+          var lPar = tokens.Dequeue();
+          if (lPar.TokenType != TokenType.LeftPar)
+            throw new ArgumentException("expected (");
+
+          // handle 'lag' specifically
+          if (funcNode.Symbol is LaggedVariable) {
+            var varId = tokens.Dequeue();
+            if (varId.TokenType != TokenType.Identifier) throw new ArgumentException("Identifier expected. Format for lagged variables: \"lag(x, -1)\"");
+            var comma = tokens.Dequeue();
+            if (comma.TokenType != TokenType.Comma) throw new ArgumentException("',' expected, Format for lagged variables: \"lag(x, -1)\"");
+            double sign = 1.0;
+            if (tokens.Peek().strVal == "+" || tokens.Peek().strVal == "-") {
+              // read sign
+              var signTok = tokens.Dequeue();
+              if (signTok.strVal == "-") sign = -1.0;
+            }
+            var lagToken = tokens.Dequeue();
+            if (lagToken.TokenType != TokenType.Number) throw new ArgumentException("Number expected, Format for lagged variables: \"lag(x, -1)\"");
+            if (!lagToken.doubleVal.IsAlmost(Math.Round(lagToken.doubleVal)))
+              throw new ArgumentException("Time lags must be integer values");
+            var laggedVarNode = funcNode as LaggedVariableTreeNode;
+            laggedVarNode.VariableName = varId.strVal;
+            laggedVarNode.Lag = (int)Math.Round(sign * lagToken.doubleVal);
+            laggedVarNode.Weight = 1.0;
+          } else {
+            // functions
+            var args = ParseArgList(tokens);
+            // check number of arguments
+            if (funcNode.Symbol.MinimumArity > args.Length || funcNode.Symbol.MaximumArity < args.Length) {
+              throw new ArgumentException(string.Format("Symbol {0} requires between {1} and  {2} arguments.", funcId,
+                funcNode.Symbol.MinimumArity, funcNode.Symbol.MaximumArity));
+            }
+            foreach (var arg in args) funcNode.AddSubtree(arg);
+          }
+
+          var rPar = tokens.Dequeue();
+          if (rPar.TokenType != TokenType.RightPar)
+            throw new ArgumentException("expected )");
+
+          return funcNode;
+        } else {
+          // variable
+          if (tokens.Peek().TokenType == TokenType.Eq) {
+            // binary factor
+            tokens.Dequeue(); // skip Eq
+            var valTok = tokens.Dequeue();
+            if (valTok.TokenType != TokenType.Identifier) throw new ArgumentException("expected identifier");
+            var binFactorNode = (BinaryFactorVariableTreeNode)binaryFactorVar.CreateTreeNode();
+            binFactorNode.Weight = 1.0;
+            binFactorNode.VariableName = idTok.strVal;
+            binFactorNode.VariableValue = valTok.strVal;
+            return binFactorNode;
+          } else if (tokens.Peek().TokenType == TokenType.LeftBracket) {
+            // factor variable
+            var factorVariableNode = (FactorVariableTreeNode)factorVar.CreateTreeNode();
+            factorVariableNode.VariableName = idTok.strVal;
+
+            tokens.Dequeue(); // skip [
+            var weights = new List<double>();
+            // at least one weight is necessary
+            var sign = 1.0;
+            if (tokens.Peek().TokenType == TokenType.Operator) {
+              var opToken = tokens.Dequeue();
+              if (opToken.strVal == "+") sign = 1.0;
+              else if (opToken.strVal == "-") sign = -1.0;
+              else throw new ArgumentException();
+            }
+            if (tokens.Peek().TokenType != TokenType.Number) throw new ArgumentException("number expected");
+            var weightTok = tokens.Dequeue();
+            weights.Add(sign * weightTok.doubleVal);
+            while (tokens.Peek().TokenType == TokenType.Comma) {
+              // skip comma
+              tokens.Dequeue();
+              if (tokens.Peek().TokenType == TokenType.Operator) {
+                var opToken = tokens.Dequeue();
+                if (opToken.strVal == "+") sign = 1.0;
+                else if (opToken.strVal == "-") sign = -1.0;
+                else throw new ArgumentException();
+              }
+              weightTok = tokens.Dequeue();
+              if (weightTok.TokenType != TokenType.Number) throw new ArgumentException("number expected");
+              weights.Add(sign * weightTok.doubleVal);
+            }
+            var rightBracketToken = tokens.Dequeue();
+            if (rightBracketToken.TokenType != TokenType.RightBracket) throw new ArgumentException("closing bracket ] expected");
+            factorVariableNode.Weights = weights.ToArray();
+            return factorVariableNode;
+          } else {
+            // variable
+            var varNode = (VariableTreeNode)variable.CreateTreeNode();
+            varNode.Weight = 1.0;
+            varNode.VariableName = idTok.strVal;
+            return varNode;
+          }
+        }
+      } else if (next.TokenType == TokenType.Number) {
+        var numTok = tokens.Dequeue();
+        var constNode = (ConstantTreeNode)constant.CreateTreeNode();
+        constNode.Value = numTok.doubleVal;
+        return constNode;
+      } else {
+        throw new ArgumentException(string.Format("unexpected token in expression {0}", next.strVal));
+      }
+    }
+
+    // ArgList = Expr { ',' Expr }
+    private ISymbolicExpressionTreeNode[] ParseArgList(Queue<Token> tokens) {
+      var exprList = new List<ISymbolicExpressionTreeNode>();
+      exprList.Add(ParseExpr(tokens));
+      while (tokens.Peek().TokenType != TokenType.RightPar) {
+        var comma = tokens.Dequeue();
+        if (comma.TokenType != TokenType.Comma) throw new ArgumentException("expected ',' ");
+        exprList.Add(ParseExpr(tokens));
+      }
+      return exprList.ToArray();
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/SymbolicExpressionImporter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/SymbolicExpressionImporter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/SymbolicExpressionImporter.cs	(revision 16337)
@@ -0,0 +1,277 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public class SymbolicExpressionImporter {
+    private const string VARSTART = "VAR";
+    private const string LAGGEDVARSTART = "LAGVARIABLE";
+    private const string INTEGRALSTART = "INTEG";
+    private const string DEFUNSTART = "DEFUN";
+    private const string ARGSTART = "ARG";
+    private const string INVOKESTART = "CALL";
+    private const string TIMELAGSTART = "LAG";
+    private Dictionary<string, Symbol> knownSymbols = new Dictionary<string, Symbol>()
+      {
+        {"+", new Addition()},
+        {"/", new Division()},
+        {"*", new Multiplication()},
+        {"-", new Subtraction()},
+        {"EXP", new Exponential()},
+        {"LOG", new Logarithm()},
+        {"POW", new Power()},
+        {"ROOT", new Root()},
+        {"SQR", new Square()},
+        {"SQRT", new SquareRoot()},
+        {"SIN",new Sine()},
+        {"COS", new Cosine()},
+        {"TAN", new Tangent()},
+        {"AIRYA", new AiryA()},
+        {"AIRYB", new AiryB()},
+        {"BESSEL", new Bessel()},
+        {"COSINT", new CosineIntegral()},
+        {"SININT", new SineIntegral()},
+        {"HYPCOSINT", new HyperbolicCosineIntegral()},
+        {"HYPSININT", new HyperbolicSineIntegral()},
+        {"FRESNELSININT", new FresnelSineIntegral()},
+        {"FRESNELCOSINT", new FresnelCosineIntegral()},
+        {"NORM", new Norm()},
+        {"ERF", new Erf()},
+        {"GAMMA", new Gamma()},
+        {"PSI", new Psi()},
+        {"DAWSON", new Dawson()},
+        {"EXPINT", new ExponentialIntegralEi()},
+        {"MEAN", new Average()},
+        {"IF", new IfThenElse()},
+        {">", new GreaterThan()},
+        {"<", new LessThan()},
+        {"AND", new And()},
+        {"OR", new Or()},
+        {"NOT", new Not()},
+        {"XOR", new Xor()},
+        {"DIFF", new Derivative()},
+        {"PROG", new ProgramRootSymbol()},
+        {"MAIN", new StartSymbol()},
+        {"FACTOR", new FactorVariable() },
+        {"BINFACTOR", new BinaryFactorVariable()}
+      };
+
+    Constant constant = new Constant();
+    Variable variable = new Variable();
+    LaggedVariable laggedVariable = new LaggedVariable();
+    Defun defun = new Defun();
+    TimeLag timeLag = new TimeLag();
+    Integral integral = new Integral();
+    FactorVariable factorVar = new FactorVariable();
+    BinaryFactorVariable binFactorVar = new BinaryFactorVariable();
+
+    ProgramRootSymbol programRootSymbol = new ProgramRootSymbol();
+    StartSymbol startSymbol = new StartSymbol();
+
+    public ISymbolicExpressionTree Import(string str) {
+      str = str.Replace("(", " ( ").Replace(")", " ) ");
+      ISymbolicExpressionTreeNode root = programRootSymbol.CreateTreeNode();
+      ISymbolicExpressionTreeNode start = startSymbol.CreateTreeNode();
+      ISymbolicExpressionTreeNode mainBranch = ParseSexp(new Queue<Token>(GetTokenStream(str)));
+      if (mainBranch.Symbol is ProgramRootSymbol) {
+        // when a root symbol was parsed => use main branch as root
+        root = mainBranch;
+      } else {
+        // only a main branch was given => insert the main branch into the default tree template
+        root.AddSubtree(start);
+        start.AddSubtree(mainBranch);
+      }
+      return new SymbolicExpressionTree(root);
+    }
+
+    private IEnumerable<Token> GetTokenStream(string str) {
+      return
+             from strToken in str.Split(new string[] { " " }, StringSplitOptions.RemoveEmptyEntries).AsEnumerable()
+             let t = Token.Parse(strToken)
+             where t != null
+             select t;
+    }
+
+    private ISymbolicExpressionTreeNode ParseSexp(Queue<Token> tokens) {
+      if (tokens.Peek().Symbol == TokenSymbol.LPAR) {
+        ISymbolicExpressionTreeNode tree;
+        Expect(Token.LPAR, tokens);
+        if (tokens.Peek().StringValue.StartsWith(VARSTART)) {
+          tree = ParseVariable(tokens);
+        } else if (tokens.Peek().StringValue.StartsWith(LAGGEDVARSTART)) {
+          tree = ParseLaggedVariable(tokens);
+        } else if (tokens.Peek().StringValue.StartsWith(TIMELAGSTART)) {
+          tree = ParseTimeLag(tokens);
+          tree.AddSubtree(ParseSexp(tokens));
+        } else if (tokens.Peek().StringValue.StartsWith(INTEGRALSTART)) {
+          tree = ParseIntegral(tokens);
+          tree.AddSubtree(ParseSexp(tokens));
+        } else if (tokens.Peek().StringValue.StartsWith(DEFUNSTART)) {
+          tree = ParseDefun(tokens);
+          while (!tokens.Peek().Equals(Token.RPAR)) {
+            tree.AddSubtree(ParseSexp(tokens));
+          }
+        } else if (tokens.Peek().StringValue.StartsWith(ARGSTART)) {
+          tree = ParseArgument(tokens);
+        } else if (tokens.Peek().StringValue.StartsWith(INVOKESTART)) {
+          tree = ParseInvoke(tokens);
+          while (!tokens.Peek().Equals(Token.RPAR)) {
+            tree.AddSubtree(ParseSexp(tokens));
+          }
+        } else if (tokens.Peek().StringValue.StartsWith("FACTOR")) {
+          tree = ParseFactor(tokens);
+        } else if (tokens.Peek().StringValue.StartsWith("BINFACTOR")) {
+          tree = ParseBinaryFactor(tokens);
+        } else {
+          Token curToken = tokens.Dequeue();
+          tree = CreateTree(curToken);
+          while (!tokens.Peek().Equals(Token.RPAR)) {
+            tree.AddSubtree(ParseSexp(tokens));
+          }
+        }
+        Expect(Token.RPAR, tokens);
+        return tree;
+      } else if (tokens.Peek().Symbol == TokenSymbol.NUMBER) {
+        ConstantTreeNode t = (ConstantTreeNode)constant.CreateTreeNode();
+        t.Value = tokens.Dequeue().DoubleValue;
+        return t;
+      } else throw new FormatException("Expected function or constant symbol");
+    }
+
+    private ISymbolicExpressionTreeNode ParseInvoke(Queue<Token> tokens) {
+      Token invokeTok = tokens.Dequeue();
+      Debug.Assert(invokeTok.StringValue == "CALL");
+      InvokeFunction invokeSym = new InvokeFunction(tokens.Dequeue().StringValue);
+      ISymbolicExpressionTreeNode invokeNode = invokeSym.CreateTreeNode();
+      return invokeNode;
+    }
+
+    private ISymbolicExpressionTreeNode ParseArgument(Queue<Token> tokens) {
+      Token argTok = tokens.Dequeue();
+      Debug.Assert(argTok.StringValue == "ARG");
+      Argument argument = new Argument((int)tokens.Dequeue().DoubleValue);
+      ISymbolicExpressionTreeNode argNode = argument.CreateTreeNode();
+      return argNode;
+    }
+
+    private ISymbolicExpressionTreeNode ParseDefun(Queue<Token> tokens) {
+      Token defTok = tokens.Dequeue();
+      Debug.Assert(defTok.StringValue == "DEFUN");
+      DefunTreeNode t = (DefunTreeNode)defun.CreateTreeNode();
+      t.FunctionName = tokens.Dequeue().StringValue;
+      return t;
+    }
+
+    private ISymbolicExpressionTreeNode ParseTimeLag(Queue<Token> tokens) {
+      Token varTok = tokens.Dequeue();
+      Debug.Assert(varTok.StringValue == "LAG");
+      LaggedTreeNode t = (LaggedTreeNode)timeLag.CreateTreeNode();
+      t.Lag = (int)tokens.Dequeue().DoubleValue;
+      return t;
+    }
+
+    private ISymbolicExpressionTreeNode ParseIntegral(Queue<Token> tokens) {
+      Token varTok = tokens.Dequeue();
+      Debug.Assert(varTok.StringValue == "INTEGRAL");
+      LaggedTreeNode t = (LaggedTreeNode)integral.CreateTreeNode();
+      t.Lag = (int)tokens.Dequeue().DoubleValue;
+      return t;
+    }
+
+    private ISymbolicExpressionTreeNode ParseVariable(Queue<Token> tokens) {
+      Token varTok = tokens.Dequeue();
+      Debug.Assert(varTok.StringValue == "VARIABLE");
+      VariableTreeNode t = (VariableTreeNode)variable.CreateTreeNode();
+      t.Weight = tokens.Dequeue().DoubleValue;
+      t.VariableName = tokens.Dequeue().StringValue;
+      return t;
+    }
+
+    private ISymbolicExpressionTreeNode ParseFactor(Queue<Token> tokens) {
+      Token tok = tokens.Dequeue();
+      Debug.Assert(tok.StringValue == "FACTOR");
+      FactorVariableTreeNode t = (FactorVariableTreeNode)(new FactorVariable()).CreateTreeNode(); // create a new symbol each time on purpose
+      var varNameTok = tokens.Dequeue();
+      Debug.Assert(tok.Symbol == TokenSymbol.SYMB);
+      t.VariableName = varNameTok.StringValue;
+
+      var weights = new List<double>();
+      while (tokens.Peek().Symbol == TokenSymbol.NUMBER) {
+        weights.Add(tokens.Dequeue().DoubleValue);
+      }
+
+      t.Weights = weights.ToArray();
+
+      // create a set of (virtual) values to match the number of weights
+      t.Symbol.VariableNames = new string[] { t.VariableName };
+      t.Symbol.VariableValues = new[]
+      { new KeyValuePair<string, Dictionary<string,int>>(
+        t.VariableName,
+        weights.Select((_, i) => Tuple.Create(_,i)).ToDictionary(tup=>"X" + tup.Item2, tup=>tup.Item2)) };
+      return t;
+    }
+
+    private ISymbolicExpressionTreeNode ParseBinaryFactor(Queue<Token> tokens) {
+      Token tok = tokens.Dequeue();
+      Debug.Assert(tok.StringValue == "BINFACTOR");
+      var t = (BinaryFactorVariableTreeNode)binFactorVar.CreateTreeNode();
+      var varNameTok = tokens.Dequeue();
+      Debug.Assert(varNameTok.Symbol == TokenSymbol.SYMB);
+      t.VariableName = varNameTok.StringValue;
+
+      var varValTok = tokens.Dequeue();
+      Debug.Assert(varValTok.Symbol == TokenSymbol.SYMB);
+      t.VariableValue = varValTok.StringValue;
+
+      var weightTok = tokens.Dequeue();
+      Debug.Assert(weightTok.Symbol == TokenSymbol.NUMBER);
+      t.Weight = weightTok.DoubleValue;
+
+      return t;
+    }
+
+
+    private ISymbolicExpressionTreeNode ParseLaggedVariable(Queue<Token> tokens) {
+      Token varTok = tokens.Dequeue();
+      Debug.Assert(varTok.StringValue == "LAGVARIABLE");
+      LaggedVariableTreeNode t = (LaggedVariableTreeNode)laggedVariable.CreateTreeNode();
+      t.Weight = tokens.Dequeue().DoubleValue;
+      t.VariableName = tokens.Dequeue().StringValue;
+      t.Lag = (int)tokens.Dequeue().DoubleValue;
+      return t;
+    }
+
+    private ISymbolicExpressionTreeNode CreateTree(Token token) {
+      if (token.Symbol != TokenSymbol.SYMB) throw new FormatException("Expected function symbol, but got: " + token.StringValue);
+      return knownSymbols[token.StringValue].CreateTreeNode();
+    }
+
+    private void Expect(Token token, Queue<Token> tokens) {
+      Token cur = tokens.Dequeue();
+      if (!token.Equals(cur)) throw new FormatException("Expected: " + token.StringValue + ", but got: " + cur.StringValue);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/Token.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/Token.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Importer/Token.cs	(revision 16337)
@@ -0,0 +1,67 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Globalization;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  internal enum TokenSymbol { LPAR, RPAR, SYMB, NUMBER };
+  internal class Token {
+    public static readonly Token LPAR = Token.Parse("(");
+    public static readonly Token RPAR = Token.Parse(")");
+
+    public TokenSymbol Symbol { get; set; }
+    public string StringValue { get; set; }
+    public double DoubleValue { get; set; }
+    public Token() { }
+
+    public override bool Equals(object obj) {
+      Token other = (obj as Token);
+      if (other == null) return false;
+      if (other.Symbol != Symbol) return false;
+      return other.StringValue == this.StringValue;
+    }
+
+    public override int GetHashCode() {
+      return Symbol.GetHashCode() & StringValue.GetHashCode();
+    }
+
+    public static Token Parse(string strToken) {
+      strToken = strToken.Trim();
+      Token t = new Token();
+      t.StringValue = strToken.Trim();
+      double temp;
+      if (strToken == "") {
+        t = null;
+      } else if (strToken == "(") {
+        t.Symbol = TokenSymbol.LPAR;
+      } else if (strToken == ")") {
+        t.Symbol = TokenSymbol.RPAR;
+      } else if (double.TryParse(strToken, NumberStyles.Float, CultureInfo.InvariantCulture.NumberFormat, out temp)) {
+        t.Symbol = TokenSymbol.NUMBER;
+        t.DoubleValue = double.Parse(strToken, CultureInfo.InvariantCulture.NumberFormat);
+      } else {
+        t.Symbol = TokenSymbol.SYMB;
+        t.StringValue = t.StringValue.ToUpper();
+      }
+      return t;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IModelBacktransformator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IModelBacktransformator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IModelBacktransformator.cs	(revision 16337)
@@ -0,0 +1,29 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface IModelBacktransformator {
+    ISymbolicDataAnalysisModel Backtransform(ISymbolicDataAnalysisModel model, IEnumerable<ITransformation> transformations, string targetVariable);
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisAnalyzer.cs	(revision 16337)
@@ -0,0 +1,31 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisAnalyzer : IAnalyzer {
+    IScopeTreeLookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter { get; }
+    ILookupParameter<ResultCollection> ResultCollectionParameter { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisBoundedOperator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisBoundedOperator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisBoundedOperator.cs	(revision 16337)
@@ -0,0 +1,27 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Core;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisBoundedOperator : IOperator {
+    IValueLookupParameter<DoubleLimit> EstimationLimitsParameter { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisEvaluator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisEvaluator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisEvaluator.cs	(revision 16337)
@@ -0,0 +1,35 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisEvaluator<T> : IEvaluator
+  where T : class,IDataAnalysisProblemData {
+    ILookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter { get; }
+    IValueLookupParameter<IntRange> EvaluationPartitionParameter { get; }
+    IValueLookupParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter { get; }
+    ILookupParameter<BoolValue> ApplyLinearScalingParameter { get; }
+
+    IValueLookupParameter<T> ProblemDataParameter { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisExpressionCrossover.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisExpressionCrossover.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisExpressionCrossover.cs	(revision 16337)
@@ -0,0 +1,35 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisExpressionCrossover<T> : ISymbolicExpressionTreeCrossover,
+    ISymbolicExpressionTreeSizeConstraintOperator, ISymbolicDataAnalysisInterpreterOperator
+    where T : class, IDataAnalysisProblemData {
+    IValueLookupParameter<T> ProblemDataParameter { get; }
+    ILookupParameter<ISymbolicDataAnalysisSingleObjectiveEvaluator<T>> EvaluatorParameter { get; }
+    IValueLookupParameter<IntRange> EvaluationPartitionParameter { get; }
+    IValueLookupParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisExpressionTreeInterpreter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisExpressionTreeInterpreter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisExpressionTreeInterpreter.cs	(revision 16337)
@@ -0,0 +1,31 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisExpressionTreeInterpreter : INamedItem, IStatefulItem {
+    IEnumerable<double> GetSymbolicExpressionTreeValues(ISymbolicExpressionTree tree, IDataset dataset, IEnumerable<int> rows);
+    int EvaluatedSolutions { get; set; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisGrammar.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisGrammar.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisGrammar.cs	(revision 16337)
@@ -0,0 +1,27 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisGrammar : ISymbolicExpressionGrammar {
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisImpactValuesCalculator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisImpactValuesCalculator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisImpactValuesCalculator.cs	(revision 16337)
@@ -0,0 +1,10 @@
+﻿using System.Collections.Generic;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisSolutionImpactValuesCalculator : IItem {
+    void CalculateImpactAndReplacementValues(ISymbolicDataAnalysisModel model, ISymbolicExpressionTreeNode node, IDataAnalysisProblemData problemData,
+      IEnumerable<int> rows, out double impactValue, out double replacementValue, out double newQualityForImpactsCalculation, double qualityForImpactsCalculation = double.NaN);
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisInterpreterOperator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisInterpreterOperator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisInterpreterOperator.cs	(revision 16337)
@@ -0,0 +1,28 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Core;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisInterpreterOperator : IOperator {
+    ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicDataAnalysisTreeInterpreterParameter { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisModel.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisModel.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisModel.cs	(revision 16337)
@@ -0,0 +1,31 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisModel : IDataAnalysisModel {
+    ISymbolicExpressionTree SymbolicExpressionTree { get; }
+    ISymbolicDataAnalysisExpressionTreeInterpreter Interpreter { get; }
+
+    double LowerEstimationLimit { get; }
+    double UpperEstimationLimit { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisMultiObjectiveAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisMultiObjectiveAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisMultiObjectiveAnalyzer.cs	(revision 16337)
@@ -0,0 +1,30 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisMultiObjectiveAnalyzer : ISymbolicDataAnalysisAnalyzer {
+    IScopeTreeLookupParameter<DoubleArray> QualitiesParameter { get; }
+    ILookupParameter<BoolArray> MaximizationParameter { get; }
+    ILookupParameter<BoolValue> ApplyLinearScalingParameter { get; }
+
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisMultiObjectiveEvaluator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisMultiObjectiveEvaluator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisMultiObjectiveEvaluator.cs	(revision 16337)
@@ -0,0 +1,34 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+
+using System.Collections.Generic;
+using HeuristicLab.Optimization;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisMultiObjectiveEvaluator<T> : ISymbolicDataAnalysisEvaluator<T>, IMultiObjectiveEvaluator
+  where T : class,IDataAnalysisProblemData {
+    IEnumerable<bool> Maximization { get; }
+    double[] Evaluate(IExecutionContext context, ISymbolicExpressionTree tree, T problemData, IEnumerable<int> rows);
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisProblem.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisProblem.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisProblem.cs	(revision 16337)
@@ -0,0 +1,51 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Optimization;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisProblem : IDataAnalysisProblem, IHeuristicOptimizationProblem {
+    IValueParameter<ISymbolicDataAnalysisGrammar> SymbolicExpressionTreeGrammarParameter { get; }
+    IValueParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicExpressionTreeInterpreterParameter { get; }
+    IFixedValueParameter<IntValue> MaximumSymbolicExpressionTreeDepthParameter { get; }
+    IFixedValueParameter<IntValue> MaximumSymbolicExpressionTreeLengthParameter { get; }
+    IFixedValueParameter<IntValue> MaximumFunctionDefinitionsParameter { get; }
+    IFixedValueParameter<IntValue> MaximumFunctionArgumentsParameter { get; }
+    IFixedValueParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter { get; }
+    IFixedValueParameter<IntRange> FitnessCalculationPartitionParameter { get; }
+    IFixedValueParameter<IntRange> ValidationPartitionParameter { get; }
+
+    ISymbolicDataAnalysisGrammar SymbolicExpressionTreeGrammar { get; set; }
+    ISymbolicDataAnalysisExpressionTreeInterpreter SymbolicExpressionTreeInterpreter { get; set; }
+    IntValue MaximumSymbolicExpressionTreeDepth { get; }
+    IntValue MaximumSymbolicExpressionTreeLength { get; }
+    IntValue MaximumFunctionDefinitions { get; }
+    IntValue MaximumFunctionArguments { get; }
+    PercentValue RelativeNumberOfEvaluatedSamples { get; }
+    IntRange FitnessCalculationPartition { get; }
+    IntRange ValidationPartition { get; }
+  }
+
+  public interface ISymbolicDataAnalysisSingleObjectiveProblem : ISymbolicDataAnalysisProblem, ISingleObjectiveHeuristicOptimizationProblem { }
+  public interface ISymbolicDataAnalysisMultiObjectiveProblem : ISymbolicDataAnalysisProblem, IMultiObjectiveHeuristicOptimizationProblem { }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSingleObjectiveAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSingleObjectiveAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSingleObjectiveAnalyzer.cs	(revision 16337)
@@ -0,0 +1,32 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisSingleObjectiveAnalyzer : ISymbolicDataAnalysisAnalyzer {
+    IScopeTreeLookupParameter<DoubleValue> QualityParameter { get; }
+    ILookupParameter<BoolValue> MaximizationParameter { get; }
+    ILookupParameter<BoolValue> ApplyLinearScalingParameter { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSingleObjectiveEvaluator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSingleObjectiveEvaluator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSingleObjectiveEvaluator.cs	(revision 16337)
@@ -0,0 +1,33 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Optimization;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using System.Collections.Generic;
+using HeuristicLab.Core;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisSingleObjectiveEvaluator<T> : ISymbolicDataAnalysisEvaluator<T>, ISingleObjectiveEvaluator
+    where T : class,IDataAnalysisProblemData {
+    bool Maximization { get; }
+
+    double Evaluate(IExecutionContext context, ISymbolicExpressionTree tree, T problemData, IEnumerable<int> rows);
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSolution.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSolution.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSolution.cs	(revision 16337)
@@ -0,0 +1,27 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisSolution : IDataAnalysisSolution {
+    new ISymbolicDataAnalysisModel Model { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSolutionCreator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSolutionCreator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisSolutionCreator.cs	(revision 16337)
@@ -0,0 +1,27 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisSolutionCreator : ISymbolicExpressionTreeCreator, ISolutionCreator {
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisValidationAnalyzer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisValidationAnalyzer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/ISymbolicDataAnalysisValidationAnalyzer.cs	(revision 16337)
@@ -0,0 +1,33 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ISymbolicDataAnalysisValidationAnalyzer<T, U> : ISymbolicDataAnalysisAnalyzer, ISymbolicDataAnalysisInterpreterOperator
+    where T : class,ISymbolicDataAnalysisEvaluator<U>
+    where U : class, IDataAnalysisProblemData {
+    ILookupParameter<IRandom> RandomParameter { get; }
+    ILookupParameter<U> ProblemDataParameter { get; }
+    ILookupParameter<T> EvaluatorParameter { get; }
+    IValueLookupParameter<IntRange> ValidationPartitionParameter { get; }
+    IValueLookupParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IVariableSymbol.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IVariableSymbol.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IVariableSymbol.cs	(revision 16337)
@@ -0,0 +1,30 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+
+  /// <summary>
+  /// Any symbol that references a variable (includes terminal as well as non-terminal symbols)
+  /// </summary>
+  public interface IVariableSymbol : ISymbol {
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IVariableTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IVariableTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interfaces/IVariableTreeNode.cs	(revision 16337)
@@ -0,0 +1,30 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Any tree node that references a variable 
+  /// </summary>
+  public interface IVariableTreeNode : ISymbolicExpressionTreeNode {
+    string VariableName { get; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/BatchInstruction.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/BatchInstruction.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/BatchInstruction.cs	(revision 16337)
@@ -0,0 +1,12 @@
+﻿namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public struct BatchInstruction {
+    public byte opcode;
+    public ushort narg;
+    public int childIndex;
+
+    public double value; // for constants
+    public double weight; // for variables
+    public double[] buf;
+    public double[] data; // to hold dataset data
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/BatchOperations.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/BatchOperations.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/BatchOperations.cs	(revision 16337)
@@ -0,0 +1,92 @@
+﻿using System;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class BatchOperations {
+    public const int BATCHSIZE = 64;
+
+    public static void Load(double[] a, double[] b) {
+      Array.Copy(b, a, BATCHSIZE);
+    }
+
+    public static void Add(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i) {
+        a[i] += b[i];
+      }
+    }
+
+    public static void Sub(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i) {
+        a[i] -= b[i];
+      }
+    }
+
+    public static void Div(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i) {
+        a[i] /= b[i];
+      }
+    }
+
+    public static void Mul(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i) {
+        a[i] *= b[i];
+      }
+    }
+
+    public static void Neg(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i) {
+        a[i] = -b[i];
+      }
+    }
+
+    public static void Inv(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i) {
+        a[i] = 1 / b[i];
+      }
+    }
+
+    public static void Log(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Log(b[i]);
+    }
+
+    public static void Exp(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Exp(b[i]);
+    }
+
+    public static void Sin(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Sin(b[i]);
+    }
+
+    public static void Cos(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Cos(b[i]);
+    }
+
+    public static void Tan(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Tan(b[i]);
+    }
+
+    public static void Pow(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Pow(a[i], Math.Round(b[i]));
+    }
+
+    public static void Root(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Pow(a[i], 1 / Math.Round(b[i]));
+    }
+
+    public static void Square(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Pow(b[i], 2d);
+    }
+
+    public static void Sqrt(double[] a, double[] b) {
+      for (int i = 0; i < BATCHSIZE; ++i)
+        a[i] = Math.Sqrt(b[i]);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/InterpreterState.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/InterpreterState.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/InterpreterState.cs	(revision 16337)
@@ -0,0 +1,93 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public class InterpreterState {
+    private readonly double[] argumentStack;
+    private int argumentStackPointer;
+    private readonly Instruction[] code;
+
+    public int ProgramCounter { get; set; }
+    public bool InLaggedContext { get; set; }
+
+    public InterpreterState(Instruction[] code, int argumentStackSize) {
+      this.code = code;
+      this.ProgramCounter = 0;
+      this.InLaggedContext = false;
+      if (argumentStackSize > 0) {
+        this.argumentStack = new double[argumentStackSize];
+      }
+      this.argumentStackPointer = 0;
+    }
+
+    public void Reset() {
+      this.ProgramCounter = 0;
+      this.argumentStackPointer = 0;
+      this.InLaggedContext = false;
+    }
+
+    public Instruction NextInstruction() {
+      return code[ProgramCounter++];
+    }
+    // skips a whole branch
+    public void SkipInstructions() {
+      int i = 1;
+      while (i > 0) {
+        i += NextInstruction().nArguments;
+        i--;
+      }
+    }
+
+    private void Push(double val) {
+      argumentStack[argumentStackPointer++] = val;
+    }
+    private double Pop() {
+      return argumentStack[--argumentStackPointer];
+    }
+
+    public void CreateStackFrame(double[] argValues) {
+      // push in reverse order to make indexing easier
+      for (int i = argValues.Length - 1; i >= 0; i--) {
+        argumentStack[argumentStackPointer++] = argValues[i];
+      }
+      Push(argValues.Length);
+    }
+
+    public void RemoveStackFrame() {
+      int size = (int)Pop();
+      argumentStackPointer -= size;
+    }
+
+    public double GetStackFrameValue(ushort index) {
+      // layout of stack:
+      // [0]   <- argumentStackPointer
+      // [StackFrameSize = N + 1]
+      // [Arg0] <- argumentStackPointer - 2 - 0
+      // [Arg1] <- argumentStackPointer - 2 - 1
+      // [...]
+      // [ArgN] <- argumentStackPointer - 2 - N
+      // <Begin of stack frame>
+      return argumentStack[argumentStackPointer - index - 2];
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/OpCodes.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/OpCodes.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/OpCodes.cs	(revision 16337)
@@ -0,0 +1,146 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class OpCodes {
+    public const byte Add = 1;
+    public const byte Sub = 2;
+    public const byte Mul = 3;
+    public const byte Div = 4;
+
+    public const byte Sin = 5;
+    public const byte Cos = 6;
+    public const byte Tan = 7;
+
+    public const byte Log = 8;
+    public const byte Exp = 9;
+
+    public const byte IfThenElse = 10;
+
+    public const byte GT = 11;
+    public const byte LT = 12;
+
+    public const byte AND = 13;
+    public const byte OR = 14;
+    public const byte NOT = 15;
+    public const byte XOR = 45;
+
+
+    public const byte Average = 16;
+
+    public const byte Call = 17;
+
+    public const byte Variable = 18;
+    public const byte LagVariable = 19;
+    public const byte Constant = 20;
+    public const byte Arg = 21;
+
+    public const byte Power = 22;
+    public const byte Root = 23;
+    public const byte TimeLag = 24;
+    public const byte Integral = 25;
+    public const byte Derivative = 26;
+
+    public const byte VariableCondition = 27;
+
+    public const byte Square = 28;
+    public const byte SquareRoot = 29;
+    public const byte Gamma = 30;
+    public const byte Psi = 31;
+    public const byte Dawson = 32;
+    public const byte ExponentialIntegralEi = 33;
+    public const byte CosineIntegral = 34;
+    public const byte SineIntegral = 35;
+    public const byte HyperbolicCosineIntegral = 36;
+    public const byte HyperbolicSineIntegral = 37;
+    public const byte FresnelCosineIntegral = 38;
+    public const byte FresnelSineIntegral = 39;
+    public const byte AiryA = 40;
+    public const byte AiryB = 41;
+    public const byte Norm = 42;
+    public const byte Erf = 43;
+    public const byte Bessel = 44;
+    public const byte FactorVariable = 46;
+    public const byte BinaryFactorVariable = 47;
+
+
+    private static Dictionary<Type, byte> symbolToOpcode = new Dictionary<Type, byte>() {
+       { typeof(Addition), OpCodes.Add },
+      { typeof(Subtraction), OpCodes.Sub },
+      { typeof(Multiplication), OpCodes.Mul },
+      { typeof(Division), OpCodes.Div },
+      { typeof(Sine), OpCodes.Sin },
+      { typeof(Cosine), OpCodes.Cos },
+      { typeof(Tangent), OpCodes.Tan },
+      { typeof(Logarithm), OpCodes.Log },
+      { typeof(Exponential), OpCodes.Exp },
+      { typeof(IfThenElse), OpCodes.IfThenElse },
+      { typeof(GreaterThan), OpCodes.GT },
+      { typeof(LessThan), OpCodes.LT },
+      { typeof(And), OpCodes.AND },
+      { typeof(Or), OpCodes.OR },
+      { typeof(Not), OpCodes.NOT},
+      { typeof(Xor),OpCodes.XOR},
+      { typeof(Average), OpCodes.Average},
+      { typeof(InvokeFunction), OpCodes.Call },
+      { typeof(Variable), OpCodes.Variable },
+      { typeof(LaggedVariable), OpCodes.LagVariable },
+      { typeof(AutoregressiveTargetVariable),OpCodes.LagVariable},
+      { typeof(Constant), OpCodes.Constant },
+      { typeof(Argument), OpCodes.Arg },
+      { typeof(Power),OpCodes.Power},
+      { typeof(Root),OpCodes.Root},
+      { typeof(TimeLag), OpCodes.TimeLag}, 
+      { typeof(Integral), OpCodes.Integral},
+      { typeof(Derivative), OpCodes.Derivative},
+      { typeof(VariableCondition),OpCodes.VariableCondition},
+      { typeof(Square),OpCodes.Square},
+      { typeof(SquareRoot),OpCodes.SquareRoot},
+      { typeof(Gamma), OpCodes.Gamma },
+      { typeof(Psi), OpCodes.Psi },
+      { typeof(Dawson), OpCodes.Dawson},
+      { typeof(ExponentialIntegralEi), OpCodes.ExponentialIntegralEi },
+      { typeof(CosineIntegral), OpCodes.CosineIntegral },
+      { typeof(SineIntegral), OpCodes.SineIntegral },
+      { typeof(HyperbolicCosineIntegral), OpCodes.HyperbolicCosineIntegral },
+      { typeof(HyperbolicSineIntegral), OpCodes.HyperbolicSineIntegral },
+      { typeof(FresnelCosineIntegral), OpCodes.FresnelCosineIntegral },
+      { typeof(FresnelSineIntegral), OpCodes.FresnelSineIntegral },
+      { typeof(AiryA), OpCodes.AiryA },
+      { typeof(AiryB), OpCodes.AiryB },
+      { typeof(Norm), OpCodes.Norm},
+      { typeof(Erf), OpCodes.Erf},
+      { typeof(Bessel), OpCodes.Bessel},
+      { typeof(FactorVariable), OpCodes.FactorVariable },
+      { typeof(BinaryFactorVariable), OpCodes.BinaryFactorVariable }
+    };
+
+    public static byte MapSymbolToOpCode(ISymbolicExpressionTreeNode treeNode) {
+      byte opCode;
+      if (symbolToOpcode.TryGetValue(treeNode.Symbol.GetType(), out opCode)) return opCode;
+      else throw new NotSupportedException("Symbol: " + treeNode.Symbol);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionCompiledTreeInterpreter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionCompiledTreeInterpreter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionCompiledTreeInterpreter.cs	(revision 16337)
@@ -0,0 +1,641 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+using System.Reflection;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicDataAnalysisExpressionCompiledTreeInterpreter", "Interpreter that converts the tree into a Linq.Expression then compiles it.")]
+  public sealed class SymbolicDataAnalysisExpressionCompiledTreeInterpreter : ParameterizedNamedItem, ISymbolicDataAnalysisExpressionTreeInterpreter {
+    private const string CheckExpressionsWithIntervalArithmeticParameterName = "CheckExpressionsWithIntervalArithmetic";
+    private const string CheckExpressionsWithIntervalArithmeticParameterDescription = "Switch that determines if the interpreter checks the validity of expressions with interval arithmetic before evaluating the expression.";
+    private const string EvaluatedSolutionsParameterName = "EvaluatedSolutions";
+
+    #region method info for the commonly called functions
+    private static readonly MethodInfo Sin = typeof(Math).GetMethod("Sin", new[] { typeof(double) });
+    private static readonly MethodInfo Cos = typeof(Math).GetMethod("Cos", new[] { typeof(double) });
+    private static readonly MethodInfo Tan = typeof(Math).GetMethod("Tan", new[] { typeof(double) });
+    private static readonly MethodInfo Sqrt = typeof(Math).GetMethod("Sqrt", new[] { typeof(double) });
+    private static readonly MethodInfo Floor = typeof(Math).GetMethod("Floor", new[] { typeof(double) });
+    private static readonly MethodInfo Round = typeof(Math).GetMethod("Round", new[] { typeof(double) });
+    private static readonly MethodInfo Exp = typeof(Math).GetMethod("Exp", new[] { typeof(double) });
+    private static readonly MethodInfo Log = typeof(Math).GetMethod("Log", new[] { typeof(double) });
+    private static readonly MethodInfo IsNaN = typeof(double).GetMethod("IsNaN");
+    private static readonly MethodInfo IsAlmost = typeof(DoubleExtensions).GetMethod("IsAlmost");
+    private static readonly MethodInfo Gamma = typeof(alglib).GetMethod("gammafunction", new[] { typeof(double) });
+    private static readonly MethodInfo Psi = typeof(alglib).GetMethod("psi", new[] { typeof(double) });
+    private static readonly MethodInfo DawsonIntegral = typeof(alglib).GetMethod("dawsonintegral", new[] { typeof(double) });
+    private static readonly MethodInfo ExponentialIntegralEi = typeof(alglib).GetMethod("exponentialintegralei", new[] { typeof(double) });
+    private static readonly MethodInfo SineCosineIntegrals = typeof(alglib).GetMethod("sinecosineintegrals", new[] { typeof(double), typeof(double).MakeByRefType(), typeof(double).MakeByRefType() });
+    private static readonly MethodInfo HyperbolicSineCosineIntegrals = typeof(alglib).GetMethod("hyperbolicsinecosineintegrals", new[] { typeof(double), typeof(double).MakeByRefType(), typeof(double).MakeByRefType() });
+    private static readonly MethodInfo FresnelIntegral = typeof(alglib).GetMethod("fresnelintegral", new[] { typeof(double), typeof(double).MakeByRefType(), typeof(double).MakeByRefType() });
+    private static readonly MethodInfo Airy = typeof(alglib).GetMethod("airy", new[] { typeof(double), typeof(double).MakeByRefType(), typeof(double).MakeByRefType(), typeof(double).MakeByRefType(), typeof(double).MakeByRefType() });
+    private static readonly MethodInfo NormalDistribution = typeof(alglib).GetMethod("normaldistribution", new[] { typeof(double) });
+    private static readonly MethodInfo ErrorFunction = typeof(alglib).GetMethod("errorfunction", new[] { typeof(double) });
+    private static readonly MethodInfo Bessel = typeof(alglib).GetMethod("besseli0", new[] { typeof(double) });
+    #endregion
+
+    public override bool CanChangeName { get { return false; } }
+    public override bool CanChangeDescription { get { return false; } }
+
+    #region parameter properties
+    public IFixedValueParameter<BoolValue> CheckExpressionsWithIntervalArithmeticParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[CheckExpressionsWithIntervalArithmeticParameterName]; }
+    }
+
+    public IFixedValueParameter<IntValue> EvaluatedSolutionsParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    public bool CheckExpressionsWithIntervalArithmetic {
+      get { return CheckExpressionsWithIntervalArithmeticParameter.Value.Value; }
+      set { CheckExpressionsWithIntervalArithmeticParameter.Value.Value = value; }
+    }
+    public int EvaluatedSolutions {
+      get { return EvaluatedSolutionsParameter.Value.Value; }
+      set { EvaluatedSolutionsParameter.Value.Value = value; }
+    }
+    #endregion
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionCompiledTreeInterpreter(this, cloner);
+    }
+
+    private SymbolicDataAnalysisExpressionCompiledTreeInterpreter(SymbolicDataAnalysisExpressionCompiledTreeInterpreter original, Cloner cloner)
+      : base(original, cloner) {
+    }
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionCompiledTreeInterpreter(bool deserializing)
+      : base(deserializing) {
+    }
+
+    public SymbolicDataAnalysisExpressionCompiledTreeInterpreter() :
+      base("SymbolicDataAnalysisExpressionCompiledTreeInterpreter", "Interpreter which compiles the tree into a lambda") {
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, CheckExpressionsWithIntervalArithmeticParameterDescription, new BoolValue(false)));
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+    }
+
+    public SymbolicDataAnalysisExpressionCompiledTreeInterpreter(string name, string description) :
+      base(name, description) {
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, CheckExpressionsWithIntervalArithmeticParameterDescription, new BoolValue(false)));
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+    }
+
+    public void InitializeState() {
+      EvaluatedSolutions = 0;
+    }
+
+    public void ClearState() { }
+
+    private readonly object syncRoot = new object();
+    public IEnumerable<double> GetSymbolicExpressionTreeValues(ISymbolicExpressionTree tree, IDataset dataset, IEnumerable<int> rows) {
+      if (CheckExpressionsWithIntervalArithmetic)
+        throw new NotSupportedException("Interval arithmetic is not yet supported in the symbolic data analysis interpreter.");
+
+      lock (syncRoot) {
+        EvaluatedSolutions++; // increment the evaluated solutions counter
+      }
+      var columns = dataset.DoubleVariables.Select(x => (IList<double>)dataset.GetReadOnlyDoubleValues(x)).ToArray();
+      var compiled = CompileTree(tree, dataset);
+      return rows.Select(x => compiled(x, columns));
+    }
+
+    public static Func<int, IList<double>[], double> CompileTree(ISymbolicExpressionTree tree, IDataset dataset) {
+      var lambda = CreateDelegate(tree, dataset);
+      return lambda.Compile();
+    }
+
+    public static Expression<Func<int, IList<double>[], double>> CreateDelegate(ISymbolicExpressionTree tree, IDataset dataset) {
+      var row = Expression.Parameter(typeof(int));
+      var columns = Expression.Parameter(typeof(IList<double>[]));
+      var variableIndices = dataset.DoubleVariables.Select((x, i) => new { x, i }).ToDictionary(e => e.x, e => e.i);
+      var expr = MakeExpr(tree, variableIndices, row, columns);
+      var lambda = Expression.Lambda<Func<int, IList<double>[], double>>(expr, row, columns);
+      return lambda;
+    }
+
+    private static Expression MakeExpr(ISymbolicExpressionTree tree, Dictionary<string, int> variableIndices, Expression row, Expression columns) {
+      var actualRoot = tree.Root.GetSubtree(0).GetSubtree(0);
+      return MakeExpr(actualRoot, variableIndices, row, columns);
+    }
+
+    private static readonly PropertyInfo Indexer = typeof(IList<double>).GetProperty("Item");
+    private static Expression MakeExpr(ISymbolicExpressionTreeNode node, Dictionary<string, int> variableIndices, Expression row, Expression columns) {
+      var opcode = OpCodes.MapSymbolToOpCode(node);
+      #region switch opcode
+      switch (opcode) {
+        case OpCodes.Constant: {
+            var constantTreeNode = (ConstantTreeNode)node;
+            return Expression.Constant(constantTreeNode.Value);
+          }
+        case OpCodes.Variable: {
+            var variableTreeNode = (VariableTreeNode)node;
+            var variableWeight = Expression.Constant(variableTreeNode.Weight);
+            var variableName = variableTreeNode.VariableName;
+            var indexExpr = Expression.Constant(variableIndices[variableName]);
+            var valuesExpr = Expression.ArrayIndex(columns, indexExpr);
+            return Expression.Multiply(variableWeight, Expression.Property(valuesExpr, Indexer, row));
+          }
+        case OpCodes.Add: {
+            Expression result = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            for (int i = 1; i < node.SubtreeCount; ++i) {
+              result = Expression.Add(result, MakeExpr(node.GetSubtree(i), variableIndices, row, columns));
+            }
+            return result;
+          }
+        case OpCodes.Sub: {
+            Expression result = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            if (node.SubtreeCount == 1)
+              return Expression.Negate(result);
+            for (int i = 1; i < node.SubtreeCount; ++i) {
+              result = Expression.Subtract(result, MakeExpr(node.GetSubtree(i), variableIndices, row, columns));
+            }
+            return result;
+          }
+        case OpCodes.Mul: {
+            Expression result = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            for (int i = 1; i < node.SubtreeCount; ++i) {
+              result = Expression.Multiply(result, MakeExpr(node.GetSubtree(i), variableIndices, row, columns));
+            }
+            return result;
+          }
+        case OpCodes.Div: {
+            Expression result = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            if (node.SubtreeCount == 1)
+              return Expression.Divide(Expression.Constant(1.0), result);
+            for (int i = 1; i < node.SubtreeCount; ++i) {
+              result = Expression.Divide(result, MakeExpr(node.GetSubtree(i), variableIndices, row, columns));
+            }
+            return result;
+          }
+        case OpCodes.Average: {
+            Expression result = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            for (int i = 1; i < node.SubtreeCount; ++i) {
+              result = Expression.Add(result, MakeExpr(node.GetSubtree(i), variableIndices, row, columns));
+            }
+            return Expression.Divide(result, Expression.Constant((double)node.SubtreeCount));
+          }
+        case OpCodes.Cos: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            return Expression.Call(Cos, arg);
+          }
+        case OpCodes.Sin: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            return Expression.Call(Sin, arg);
+          }
+        case OpCodes.Tan: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            return Expression.Call(Tan, arg);
+          }
+        case OpCodes.Square: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            return Expression.Power(arg, Expression.Constant(2.0));
+          }
+        case OpCodes.Power: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var power = MakeExpr(node.GetSubtree(1), variableIndices, row, columns);
+            return Expression.Power(arg, Expression.Call(Round, power));
+          }
+        case OpCodes.SquareRoot: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            return Expression.Call(Sqrt, arg);
+          }
+        case OpCodes.Root: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var power = MakeExpr(node.GetSubtree(1), variableIndices, row, columns);
+            return Expression.Power(arg, Expression.Divide(Expression.Constant(1.0), Expression.Call(Round, power)));
+          }
+        case OpCodes.Exp: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            return Expression.Call(Exp, arg);
+          }
+        case OpCodes.Log: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            return Expression.Call(Log, arg);
+          }
+        case OpCodes.Gamma: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(
+              new[] { result },
+              Expression.IfThenElse(
+                isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, Expression.Call(Gamma, arg))
+                ),
+              result
+              );
+            return expr;
+          }
+        case OpCodes.Psi: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+
+            var result = Expression.Variable(typeof(double));
+            var floor = Expression.Call(Floor, arg);
+            var expr = Expression.Block(
+              new[] { result },
+              Expression.IfThenElse(
+                isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.IfThenElse(
+                  Expression.AndAlso(
+                    Expression.LessThanOrEqual(arg, Expression.Constant(0.0)),
+                    Expression.Call(IsAlmost, Expression.Subtract(floor, arg), Expression.Constant(0.0))),
+                  Expression.Assign(result, Expression.Constant(double.NaN)),
+                  Expression.Assign(result, Expression.Call(Psi, arg)))
+                ),
+              result);
+
+            return expr;
+          }
+        case OpCodes.Dawson: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(
+              new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, Expression.Call(DawsonIntegral, arg))),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.ExponentialIntegralEi: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(
+              new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, Expression.Call(ExponentialIntegralEi, arg))),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.SineIntegral: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var si = Expression.Variable(typeof(double));
+            var ci = Expression.Variable(typeof(double));
+            var block = Expression.Block(
+              new[] { si, ci },
+              Expression.Call(SineCosineIntegrals, arg, si, ci),
+              si
+              );
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, block)),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.CosineIntegral: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var si = Expression.Variable(typeof(double));
+            var ci = Expression.Variable(typeof(double));
+            var block = Expression.Block(
+              new[] { si, ci },
+              Expression.Call(SineCosineIntegrals, arg, si, ci),
+              ci
+              );
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, block)),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.HyperbolicSineIntegral: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var shi = Expression.Variable(typeof(double));
+            var chi = Expression.Variable(typeof(double));
+            var block = Expression.Block(
+              new[] { shi, chi },
+              Expression.Call(HyperbolicSineCosineIntegrals, arg, shi, chi),
+              shi
+              );
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, block)),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.HyperbolicCosineIntegral: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var shi = Expression.Variable(typeof(double));
+            var chi = Expression.Variable(typeof(double));
+            var block = Expression.Block(
+              new[] { shi, chi },
+              Expression.Call(HyperbolicSineCosineIntegrals, arg, shi, chi),
+              chi
+              );
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, block)),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.FresnelSineIntegral: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var s = Expression.Variable(typeof(double));
+            var c = Expression.Variable(typeof(double));
+            var block = Expression.Block(new[] { s, c }, Expression.Call(FresnelIntegral, arg, c, s), s);
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, block)),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.FresnelCosineIntegral: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var s = Expression.Variable(typeof(double));
+            var c = Expression.Variable(typeof(double));
+            var block = Expression.Block(new[] { s, c }, Expression.Call(FresnelIntegral, arg, c, s), c);
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, block)),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.AiryA: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var ai = Expression.Variable(typeof(double));
+            var aip = Expression.Variable(typeof(double));
+            var bi = Expression.Variable(typeof(double));
+            var bip = Expression.Variable(typeof(double));
+            var block = Expression.Block(new[] { ai, aip, bi, bip }, Expression.Call(Airy, arg, ai, aip, bi, bip), ai);
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, block)),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.AiryB: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var ai = Expression.Variable(typeof(double));
+            var aip = Expression.Variable(typeof(double));
+            var bi = Expression.Variable(typeof(double));
+            var bip = Expression.Variable(typeof(double));
+            var block = Expression.Block(new[] { ai, aip, bi, bip }, Expression.Call(Airy, arg, ai, aip, bi, bip), bi);
+            var result = Expression.Variable(typeof(double));
+            var expr = Expression.Block(new[] { result },
+              Expression.IfThenElse(isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, block)),
+              result
+              );
+
+            return expr;
+          }
+        case OpCodes.Norm: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var result = Expression.Variable(typeof(double));
+            return Expression.Block(
+              new[] { result },
+              Expression.IfThenElse(
+                Expression.Call(IsNaN, arg),
+                Expression.Assign(result, arg),
+                Expression.Assign(result, Expression.Call(NormalDistribution, arg))),
+              result);
+          }
+        case OpCodes.Erf: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var result = Expression.Variable(typeof(double));
+            return Expression.Block(
+              new[] { result },
+              Expression.IfThenElse(
+                isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, Expression.Call(ErrorFunction, arg))),
+              result);
+          }
+        case OpCodes.Bessel: {
+            var arg = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var isNaN = Expression.Call(IsNaN, arg);
+            var result = Expression.Variable(typeof(double));
+            return Expression.Block(
+              new[] { result },
+              Expression.IfThenElse(
+                isNaN,
+                Expression.Assign(result, Expression.Constant(double.NaN)),
+                Expression.Assign(result, Expression.Call(Bessel, arg))),
+              result);
+          }
+        case OpCodes.IfThenElse: {
+            var test = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var result = Expression.Variable(typeof(double));
+            var condition = Expression.IfThenElse(Expression.GreaterThan(test, Expression.Constant(0.0)),
+              Expression.Assign(result, MakeExpr(node.GetSubtree(1), variableIndices, row, columns)),
+              Expression.Assign(result, MakeExpr(node.GetSubtree(2), variableIndices, row, columns)));
+            return Expression.Block(new[] { result }, condition, result);
+          }
+        case OpCodes.AND: {
+            var result = Expression.Variable(typeof(double));
+            var expr = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+
+            for (int i = 1; i < node.SubtreeCount; ++i) {
+              expr = Expression.Block(new[] { result },
+                Expression.IfThenElse(
+                  Expression.GreaterThan(expr, Expression.Constant(0.0)),
+                  Expression.Assign(result, MakeExpr(node.GetSubtree(i), variableIndices, row, columns)),
+                  Expression.Assign(result, expr)),
+                result
+                );
+            }
+
+            return Expression.Block(
+              new[] { result },
+              Expression.Assign(result, expr),
+              Expression.IfThenElse(
+                Expression.GreaterThan(result, Expression.Constant(0.0)),
+                Expression.Assign(result, Expression.Constant(1.0)),
+                Expression.Assign(result, Expression.Constant(-1.0))
+                ),
+              result
+              );
+          }
+        case OpCodes.OR: {
+            var result = Expression.Variable(typeof(double));
+            var expr = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+
+            for (int i = 1; i < node.SubtreeCount; ++i) {
+              expr = Expression.Block(new[] { result },
+                Expression.IfThenElse(
+                  Expression.LessThanOrEqual(expr, Expression.Constant(0.0)),
+                  Expression.Assign(result, MakeExpr(node.GetSubtree(i), variableIndices, row, columns)),
+                  Expression.Assign(result, expr)),
+                result
+                );
+            }
+
+            return Expression.Block(
+              new[] { result },
+              Expression.Assign(result, expr),
+              Expression.IfThenElse(
+                Expression.GreaterThan(result, Expression.Constant(0.0)),
+                Expression.Assign(result, Expression.Constant(1.0)),
+                Expression.Assign(result, Expression.Constant(-1.0))
+                ),
+              result
+              );
+          }
+        case OpCodes.NOT: {
+            var value = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var result = Expression.Variable(typeof(double));
+            var condition = Expression.IfThenElse(Expression.GreaterThan(value, Expression.Constant(0.0)),
+              Expression.Assign(result, Expression.Constant(-1.0)),
+              Expression.Assign(result, Expression.Constant(1.0)));
+            return Expression.Block(new[] { result }, condition, result);
+          }
+        case OpCodes.XOR: {
+            var ps = Expression.Variable(typeof(int));
+            var block = Expression.Block(
+              new[] { ps },
+              Expression.Assign(ps, Expression.Constant(0)),
+              ps
+              );
+
+            foreach (var subtree in node.Subtrees) {
+              var expr = MakeExpr(subtree, variableIndices, row, columns);
+              block = Expression.Block(
+                new[] { ps },
+                Expression.Assign(ps, block),
+                Expression.IfThen(Expression.GreaterThan(expr, Expression.Constant(0.0)),
+                  Expression.PostIncrementAssign(ps)),
+                ps
+                );
+            }
+
+            var result = Expression.Variable(typeof(double));
+            var xorExpr = Expression.Block(
+              new[] { result },
+              Expression.IfThenElse(
+                Expression.Equal(Expression.Modulo(block, Expression.Constant(2)), Expression.Constant(0)),
+                Expression.Assign(result, Expression.Constant(-1.0)),
+                Expression.Assign(result, Expression.Constant(1.0))
+                ),
+              result
+              );
+            return xorExpr;
+          }
+        case OpCodes.GT: {
+            var left = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var right = MakeExpr(node.GetSubtree(1), variableIndices, row, columns);
+            var result = Expression.Variable(typeof(double));
+
+            var condition = Expression.IfThenElse(Expression.GreaterThan(left, right),
+              Expression.Assign(result, Expression.Constant(1.0)), Expression.Assign(result, Expression.Constant(-1.0)));
+            return Expression.Block(
+              new[] { result },
+              condition,
+              result);
+          }
+        case OpCodes.LT: {
+            var left = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var right = MakeExpr(node.GetSubtree(1), variableIndices, row, columns);
+            var result = Expression.Variable(typeof(double));
+
+            var condition = Expression.IfThenElse(Expression.LessThan(left, right),
+              Expression.Assign(result, Expression.Constant(1.0)), Expression.Assign(result, Expression.Constant(-1.0)));
+            return Expression.Block(new[] { result }, condition, result);
+          }
+        case OpCodes.VariableCondition: {
+            var variableConditionTreeNode = (VariableConditionTreeNode)node;
+            if (variableConditionTreeNode.Symbol.IgnoreSlope) throw new NotSupportedException("Strict variable conditionals are not supported");
+            var variableName = variableConditionTreeNode.VariableName;
+            var indexExpr = Expression.Constant(variableIndices[variableName]);
+            var valuesExpr = Expression.ArrayIndex(columns, indexExpr);
+            var variableValue = Expression.Property(valuesExpr, Indexer, row);
+            var variableThreshold = Expression.Constant(variableConditionTreeNode.Threshold);
+            var variableSlope = Expression.Constant(variableConditionTreeNode.Slope);
+
+            var x = Expression.Subtract(variableValue, variableThreshold);
+            var xSlope = Expression.Multiply(Expression.Negate(variableSlope), x);
+            var xSlopeExp = Expression.Call(Exp, xSlope);
+            var p = Expression.Divide(Expression.Constant(1), Expression.Add(Expression.Constant(1), xSlopeExp));
+            var trueBranch = MakeExpr(node.GetSubtree(0), variableIndices, row, columns);
+            var falseBranch = MakeExpr(node.GetSubtree(1), variableIndices, row, columns);
+            return Expression.Add(
+              Expression.Multiply(trueBranch, p),
+              Expression.Multiply(falseBranch, Expression.Subtract(Expression.Constant(1), p))
+              );
+          }
+        default:
+          throw new NotSupportedException("Unsupported symbol: " + node.Symbol);
+      }
+      #endregion
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeBatchInterpreter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeBatchInterpreter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeBatchInterpreter.cs	(revision 16337)
@@ -0,0 +1,233 @@
+﻿using System;
+using System.Collections.Generic;
+using System.Linq;
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+using static HeuristicLab.Problems.DataAnalysis.Symbolic.BatchOperations;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("SymbolicDataAnalysisExpressionTreeBatchInterpreter", "An interpreter that uses batching and vectorization techniques to achieve faster performance.")]
+  [StorableClass]
+  public class SymbolicDataAnalysisExpressionTreeBatchInterpreter : ParameterizedNamedItem, ISymbolicDataAnalysisExpressionTreeInterpreter {
+    private const string EvaluatedSolutionsParameterName = "EvaluatedSolutions";
+
+    #region parameters
+    public IFixedValueParameter<IntValue> EvaluatedSolutionsParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    public int EvaluatedSolutions {
+      get { return EvaluatedSolutionsParameter.Value.Value; }
+      set { EvaluatedSolutionsParameter.Value.Value = value; }
+    }
+    #endregion
+
+    public void ClearState() { }
+
+    public SymbolicDataAnalysisExpressionTreeBatchInterpreter() {
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+    }
+
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionTreeBatchInterpreter(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisExpressionTreeBatchInterpreter(SymbolicDataAnalysisExpressionTreeBatchInterpreter original, Cloner cloner) : base(original, cloner) {
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionTreeBatchInterpreter(this, cloner);
+    }
+
+    private void LoadData(BatchInstruction instr, int[] rows, int rowIndex, int batchSize) {
+      for (int i = 0; i < batchSize; ++i) {
+        var row = rows[rowIndex] + i;
+        instr.buf[i] = instr.weight * instr.data[row];
+      }
+    }
+
+    private void Evaluate(BatchInstruction[] code, int[] rows, int rowIndex, int batchSize) {
+      for (int i = code.Length - 1; i >= 0; --i) {
+        var instr = code[i];
+        var c = instr.childIndex;
+        var n = instr.narg;
+
+        switch (instr.opcode) {
+          case OpCodes.Variable: {
+              LoadData(instr, rows, rowIndex, batchSize);
+              break;
+            }
+
+          case OpCodes.Add: {
+              Load(instr.buf, code[c].buf);
+              for (int j = 1; j < n; ++j) {
+                Add(instr.buf, code[c + j].buf);
+              }
+              break;
+            }
+
+          case OpCodes.Sub: {
+              if (n == 1) {
+                Neg(instr.buf, code[c].buf);
+              } else {
+                Load(instr.buf, code[c].buf);
+                for (int j = 1; j < n; ++j) {
+                  Sub(instr.buf, code[c + j].buf);
+                }
+              }
+              break;
+            }
+
+          case OpCodes.Mul: {
+              Load(instr.buf, code[c].buf);
+              for (int j = 1; j < n; ++j) {
+                Mul(instr.buf, code[c + j].buf);
+              }
+              break;
+            }
+
+          case OpCodes.Div: {
+              if (n == 1) {
+                Inv(instr.buf, code[c].buf);
+              } else {
+                Load(instr.buf, code[c].buf);
+                for (int j = 1; j < n; ++j) {
+                  Div(instr.buf, code[c + j].buf);
+                }
+              }
+              break;
+            }
+
+          case OpCodes.Square: {
+              Square(instr.buf, code[c].buf);
+              break;
+            }
+
+          case OpCodes.Root: {
+              Root(instr.buf, code[c].buf);
+              break;
+            }
+
+          case OpCodes.SquareRoot: {
+              Sqrt(instr.buf, code[c].buf);
+              break;
+            }
+
+          case OpCodes.Power: {
+              Pow(instr.buf, code[c].buf);
+              break;
+            }
+
+          case OpCodes.Exp: {
+              Exp(instr.buf, code[c].buf);
+              break;
+            }
+
+          case OpCodes.Log: {
+              Log(instr.buf, code[c].buf);
+              break;
+            }
+
+          case OpCodes.Sin: {
+              Sin(instr.buf, code[c].buf);
+              break;
+            }
+
+          case OpCodes.Cos: {
+              Cos(instr.buf, code[c].buf);
+              break;
+            }
+
+          case OpCodes.Tan: {
+              Tan(instr.buf, code[c].buf);
+              break;
+            }
+        }
+      }
+    }
+
+    [ThreadStatic]
+    private Dictionary<string, double[]> cachedData;
+
+    private void InitCache(IDataset dataset) {
+      cachedData = new Dictionary<string, double[]>();
+      foreach (var v in dataset.DoubleVariables) {
+        cachedData[v] = dataset.GetDoubleValues(v).ToArray();
+      }
+    }
+
+    public void InitializeState() {
+      cachedData = null;
+      EvaluatedSolutions = 0;
+    }
+
+    private double[] GetValues(ISymbolicExpressionTree tree, IDataset dataset, int[] rows) {
+      var code = Compile(tree, dataset, OpCodes.MapSymbolToOpCode);
+      var remainingRows = rows.Length % BATCHSIZE;
+      var roundedTotal = rows.Length - remainingRows;
+
+      var result = new double[rows.Length];
+
+      for (int rowIndex = 0; rowIndex < roundedTotal; rowIndex += BATCHSIZE) {
+        Evaluate(code, rows, rowIndex, BATCHSIZE);
+        Array.Copy(code[0].buf, 0, result, rowIndex, BATCHSIZE);
+      }
+
+      if (remainingRows > 0) {
+        Evaluate(code, rows, roundedTotal, remainingRows);
+        Array.Copy(code[0].buf, 0, result, roundedTotal, remainingRows);
+      }
+
+      return result;
+    }
+
+    public IEnumerable<double> GetSymbolicExpressionTreeValues(ISymbolicExpressionTree tree, IDataset dataset, int[] rows) {
+      if (cachedData == null) {
+        InitCache(dataset);
+      }
+      return GetValues(tree, dataset, rows);
+    }
+
+    public IEnumerable<double> GetSymbolicExpressionTreeValues(ISymbolicExpressionTree tree, IDataset dataset, IEnumerable<int> rows) {
+      return GetSymbolicExpressionTreeValues(tree, dataset, rows.ToArray());
+    }
+
+    private BatchInstruction[] Compile(ISymbolicExpressionTree tree, IDataset dataset, Func<ISymbolicExpressionTreeNode, byte> opCodeMapper) {
+      var root = tree.Root.GetSubtree(0).GetSubtree(0);
+      var code = new BatchInstruction[root.GetLength()];
+      if (root.SubtreeCount > ushort.MaxValue) throw new ArgumentException("Number of subtrees is too big (>65.535)");
+      int c = 1, i = 0;
+      foreach (var node in root.IterateNodesBreadth()) {
+        if (node.SubtreeCount > ushort.MaxValue) throw new ArgumentException("Number of subtrees is too big (>65.535)");
+        code[i] = new BatchInstruction {
+          opcode = opCodeMapper(node),
+          narg = (ushort)node.SubtreeCount,
+          buf = new double[BATCHSIZE],
+          childIndex = c
+        };
+        if (node is VariableTreeNode variable) {
+          code[i].weight = variable.Weight;
+          if (cachedData.ContainsKey(variable.VariableName)) {
+            code[i].data = cachedData[variable.VariableName];
+          } else {
+            code[i].data = dataset.GetReadOnlyDoubleValues(variable.VariableName).ToArray();
+            cachedData[variable.VariableName] = code[i].data;
+          }
+        } else if (node is ConstantTreeNode constant) {
+          code[i].value = constant.Value;
+          for (int j = 0; j < BATCHSIZE; ++j)
+            code[i].buf[j] = code[i].value;
+        }
+        c += node.SubtreeCount;
+        ++i;
+      }
+      return code;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeILEmittingInterpreter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeILEmittingInterpreter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeILEmittingInterpreter.cs	(revision 16337)
@@ -0,0 +1,772 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Reflection;
+using System.Reflection.Emit;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicDataAnalysisExpressionTreeILEmittingInterpreter", "Interpreter for symbolic expression trees.")]
+  public sealed class SymbolicDataAnalysisExpressionTreeILEmittingInterpreter : ParameterizedNamedItem, ISymbolicDataAnalysisExpressionTreeInterpreter {
+    private static readonly Type thisType = typeof(SymbolicDataAnalysisExpressionTreeILEmittingInterpreter);
+    internal delegate double CompiledFunction(int sampleIndex, IList<double>[] columns);
+
+    #region method infos
+    private static MethodInfo listGetValue = typeof(IList<double>).GetProperty("Item", new Type[] { typeof(int) }).GetGetMethod();
+
+    private static MethodInfo cos = typeof(Math).GetMethod("Cos", new Type[] { typeof(double) });
+    private static MethodInfo sin = typeof(Math).GetMethod("Sin", new Type[] { typeof(double) });
+    private static MethodInfo tan = typeof(Math).GetMethod("Tan", new Type[] { typeof(double) });
+    private static MethodInfo exp = typeof(Math).GetMethod("Exp", new Type[] { typeof(double) });
+    private static MethodInfo log = typeof(Math).GetMethod("Log", new Type[] { typeof(double) });
+    private static MethodInfo power = typeof(Math).GetMethod("Pow", new Type[] { typeof(double), typeof(double) });
+    private static MethodInfo round = typeof(Math).GetMethod("Round", new Type[] { typeof(double) });
+    private static MethodInfo sqrt = typeof(Math).GetMethod("Sqrt", new Type[] { typeof(double) });
+
+    private static MethodInfo airyA = thisType.GetMethod("AiryA", new Type[] { typeof(double) });
+    private static MethodInfo airyB = thisType.GetMethod("AiryB", new Type[] { typeof(double) });
+    private static MethodInfo gamma = thisType.GetMethod("Gamma", new Type[] { typeof(double) });
+    private static MethodInfo psi = thisType.GetMethod("Psi", new Type[] { typeof(double) });
+    private static MethodInfo dawson = thisType.GetMethod("Dawson", new Type[] { typeof(double) });
+    private static MethodInfo expIntegralEi = thisType.GetMethod("ExpIntegralEi", new Type[] { typeof(double) });
+    private static MethodInfo sinIntegral = thisType.GetMethod("SinIntegral", new Type[] { typeof(double) });
+    private static MethodInfo cosIntegral = thisType.GetMethod("CosIntegral", new Type[] { typeof(double) });
+    private static MethodInfo hypSinIntegral = thisType.GetMethod("HypSinIntegral", new Type[] { typeof(double) });
+    private static MethodInfo hypCosIntegral = thisType.GetMethod("HypCosIntegral", new Type[] { typeof(double) });
+    private static MethodInfo fresnelCosIntegral = thisType.GetMethod("FresnelCosIntegral", new Type[] { typeof(double) });
+    private static MethodInfo fresnelSinIntegral = thisType.GetMethod("FresnelSinIntegral", new Type[] { typeof(double) });
+    private static MethodInfo norm = thisType.GetMethod("Norm", new Type[] { typeof(double) });
+    private static MethodInfo erf = thisType.GetMethod("Erf", new Type[] { typeof(double) });
+    private static MethodInfo bessel = thisType.GetMethod("Bessel", new Type[] { typeof(double) });
+    private static MethodInfo string_eq = typeof(string).GetMethod("Equals", new Type[] { typeof(string) });
+    #endregion
+
+    private const string CheckExpressionsWithIntervalArithmeticParameterName = "CheckExpressionsWithIntervalArithmetic";
+    private const string CheckExpressionsWithIntervalArithmeticParameterDescription = "Switch that determines if the interpreter checks the validity of expressions with interval arithmetic before evaluating the expression.";
+    private const string EvaluatedSolutionsParameterName = "EvaluatedSolutions";
+
+    public override bool CanChangeName {
+      get { return false; }
+    }
+
+    public override bool CanChangeDescription {
+      get { return false; }
+    }
+
+    #region parameter properties
+    public IFixedValueParameter<BoolValue> CheckExpressionsWithIntervalArithmeticParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[CheckExpressionsWithIntervalArithmeticParameterName]; }
+    }
+
+    public IFixedValueParameter<IntValue> EvaluatedSolutionsParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    public bool CheckExpressionsWithIntervalArithmetic {
+      get { return CheckExpressionsWithIntervalArithmeticParameter.Value.Value; }
+      set { CheckExpressionsWithIntervalArithmeticParameter.Value.Value = value; }
+    }
+    public int EvaluatedSolutions {
+      get { return EvaluatedSolutionsParameter.Value.Value; }
+      set { EvaluatedSolutionsParameter.Value.Value = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionTreeILEmittingInterpreter(bool deserializing) : base(deserializing) { }
+
+    private SymbolicDataAnalysisExpressionTreeILEmittingInterpreter(SymbolicDataAnalysisExpressionTreeILEmittingInterpreter original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionTreeILEmittingInterpreter(this, cloner);
+    }
+
+    public SymbolicDataAnalysisExpressionTreeILEmittingInterpreter()
+      : base("SymbolicDataAnalysisExpressionTreeILEmittingInterpreter", "Interpreter for symbolic expression trees.") {
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName,
+        "Switch that determines if the interpreter checks the validity of expressions with interval arithmetic before evaluating the expression.", new BoolValue(false)));
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+    }
+
+    public SymbolicDataAnalysisExpressionTreeILEmittingInterpreter(string name, string description)
+      : base(name, description) {
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName,
+        "Switch that determines if the interpreter checks the validity of expressions with interval arithmetic before evaluating the expression.", new BoolValue(false)));
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      var evaluatedSolutions = new IntValue(0);
+      var checkExpressionsWithIntervalArithmetic = new BoolValue(false);
+      if (Parameters.ContainsKey(EvaluatedSolutionsParameterName)) {
+        var evaluatedSolutionsParameter = (IValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName];
+        evaluatedSolutions = evaluatedSolutionsParameter.Value;
+        Parameters.Remove(EvaluatedSolutionsParameterName);
+      }
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", evaluatedSolutions));
+      if (Parameters.ContainsKey(CheckExpressionsWithIntervalArithmeticParameterName)) {
+        var checkExpressionsWithIntervalArithmeticParameter = (IValueParameter<BoolValue>)Parameters[CheckExpressionsWithIntervalArithmeticParameterName];
+        Parameters.Remove(CheckExpressionsWithIntervalArithmeticParameterName);
+        checkExpressionsWithIntervalArithmetic = checkExpressionsWithIntervalArithmeticParameter.Value;
+      }
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, CheckExpressionsWithIntervalArithmeticParameterDescription, checkExpressionsWithIntervalArithmetic));
+    }
+
+    #region IStatefulItem
+    public void InitializeState() {
+      EvaluatedSolutions = 0;
+    }
+
+    public void ClearState() {
+    }
+    #endregion
+
+    private readonly object syncRoot = new object();
+    public IEnumerable<double> GetSymbolicExpressionTreeValues(ISymbolicExpressionTree tree, IDataset dataset, IEnumerable<int> rows) {
+      if (CheckExpressionsWithIntervalArithmetic)
+        throw new NotSupportedException("Interval arithmetic is not yet supported in the symbolic data analysis interpreter.");
+
+      lock (syncRoot) {
+        EvaluatedSolutions++; // increment the evaluated solutions counter
+      }
+      var state = PrepareInterpreterState(tree, dataset);
+
+      Type[] methodArgs = { typeof(int), typeof(IList<double>[]) };
+      DynamicMethod testFun = new DynamicMethod("TestFun", typeof(double), methodArgs, typeof(SymbolicDataAnalysisExpressionTreeILEmittingInterpreter).Module);
+
+      ILGenerator il = testFun.GetILGenerator();
+      CompileInstructions(il, state, dataset);
+      il.Emit(System.Reflection.Emit.OpCodes.Conv_R8);
+      il.Emit(System.Reflection.Emit.OpCodes.Ret);
+      var function = (CompiledFunction)testFun.CreateDelegate(typeof(CompiledFunction));
+
+      IList<double>[] columns = dataset.DoubleVariables.Select(v => dataset.GetReadOnlyDoubleValues(v)).ToArray();
+
+      foreach (var row in rows) {
+        yield return function(row, columns);
+      }
+    }
+
+    private InterpreterState PrepareInterpreterState(ISymbolicExpressionTree tree, IDataset dataset) {
+      Instruction[] code = SymbolicExpressionTreeCompiler.Compile(tree, OpCodes.MapSymbolToOpCode);
+      Dictionary<string, int> doubleVariableNames = dataset.DoubleVariables.Select((x, i) => new { x, i }).ToDictionary(e => e.x, e => e.i);
+      int necessaryArgStackSize = 0;
+      foreach (Instruction instr in code) {
+        if (instr.opCode == OpCodes.Variable) {
+          var variableTreeNode = (VariableTreeNode)instr.dynamicNode;
+          instr.data = doubleVariableNames[variableTreeNode.VariableName];
+        } else if (instr.opCode == OpCodes.LagVariable) {
+          var laggedVariableTreeNode = (LaggedVariableTreeNode)instr.dynamicNode;
+          instr.data = doubleVariableNames[laggedVariableTreeNode.VariableName];
+        } else if (instr.opCode == OpCodes.VariableCondition) {
+          var variableConditionTreeNode = (VariableConditionTreeNode)instr.dynamicNode;
+          instr.data = doubleVariableNames[variableConditionTreeNode.VariableName];
+        } else if (instr.opCode == OpCodes.Call) {
+          necessaryArgStackSize += instr.nArguments + 1;
+        }
+      }
+      return new InterpreterState(code, necessaryArgStackSize);
+    }
+
+    private void CompileInstructions(ILGenerator il, InterpreterState state, IDataset ds) {
+      Instruction currentInstr = state.NextInstruction();
+      int nArgs = currentInstr.nArguments;
+
+      switch (currentInstr.opCode) {
+        case OpCodes.Add: {
+            if (nArgs > 0) {
+              CompileInstructions(il, state, ds);
+            }
+            for (int i = 1; i < nArgs; i++) {
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Add);
+            }
+            return;
+          }
+        case OpCodes.Sub: {
+            if (nArgs == 1) {
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Neg);
+              return;
+            }
+            if (nArgs > 0) {
+              CompileInstructions(il, state, ds);
+            }
+            for (int i = 1; i < nArgs; i++) {
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Sub);
+            }
+            return;
+          }
+        case OpCodes.Mul: {
+            if (nArgs > 0) {
+              CompileInstructions(il, state, ds);
+            }
+            for (int i = 1; i < nArgs; i++) {
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            }
+            return;
+          }
+        case OpCodes.Div: {
+            if (nArgs == 1) {
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0);
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Div);
+              return;
+            }
+            if (nArgs > 0) {
+              CompileInstructions(il, state, ds);
+            }
+            for (int i = 1; i < nArgs; i++) {
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Div);
+            }
+            return;
+          }
+        case OpCodes.Average: {
+            CompileInstructions(il, state, ds);
+            for (int i = 1; i < nArgs; i++) {
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Add);
+            }
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, (double)nArgs);
+            il.Emit(System.Reflection.Emit.OpCodes.Div);
+            return;
+          }
+        case OpCodes.Cos: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, cos);
+            return;
+          }
+        case OpCodes.Sin: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, sin);
+            return;
+          }
+        case OpCodes.Tan: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, tan);
+            return;
+          }
+        case OpCodes.Power: {
+            CompileInstructions(il, state, ds);
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, round);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, power);
+            return;
+          }
+        case OpCodes.Root: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // 1 / round(...)
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, round);
+            il.Emit(System.Reflection.Emit.OpCodes.Div);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, power);
+            return;
+          }
+        case OpCodes.Exp: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, exp);
+            return;
+          }
+        case OpCodes.Log: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, log);
+            return;
+          }
+        case OpCodes.Square: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 2.0);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, power);
+            return;
+          }
+        case OpCodes.SquareRoot: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, sqrt);
+            return;
+          }
+        case OpCodes.AiryA: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, airyA);
+            return;
+          }
+        case OpCodes.AiryB: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, airyB);
+            return;
+          }
+        case OpCodes.Bessel: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, bessel);
+            return;
+          }
+        case OpCodes.CosineIntegral: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, cosIntegral);
+            return;
+          }
+        case OpCodes.Dawson: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, dawson);
+            return;
+          }
+        case OpCodes.Erf: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, erf);
+            return;
+          }
+        case OpCodes.ExponentialIntegralEi: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, expIntegralEi);
+            return;
+          }
+        case OpCodes.FresnelCosineIntegral: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, fresnelCosIntegral);
+            return;
+          }
+        case OpCodes.FresnelSineIntegral: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, fresnelSinIntegral);
+            return;
+          }
+        case OpCodes.Gamma: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, gamma);
+            return;
+          }
+        case OpCodes.HyperbolicCosineIntegral: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, hypCosIntegral);
+            return;
+          }
+        case OpCodes.HyperbolicSineIntegral: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, hypSinIntegral);
+            return;
+          }
+        case OpCodes.Norm: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, norm);
+            return;
+          }
+        case OpCodes.Psi: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, psi);
+            return;
+          }
+        case OpCodes.SineIntegral: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, sinIntegral);
+            return;
+          }
+        case OpCodes.IfThenElse: {
+            Label end = il.DefineLabel();
+            Label c1 = il.DefineLabel();
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0); // > 0
+            il.Emit(System.Reflection.Emit.OpCodes.Cgt);
+            il.Emit(System.Reflection.Emit.OpCodes.Brfalse, c1);
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Br, end);
+            il.MarkLabel(c1);
+            CompileInstructions(il, state, ds);
+            il.MarkLabel(end);
+            return;
+          }
+        case OpCodes.AND: {
+            Label falseBranch = il.DefineLabel();
+            Label end = il.DefineLabel();
+            CompileInstructions(il, state, ds);
+            for (int i = 1; i < nArgs; i++) {
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0); // > 0
+              il.Emit(System.Reflection.Emit.OpCodes.Cgt);
+              il.Emit(System.Reflection.Emit.OpCodes.Brfalse, falseBranch);
+              CompileInstructions(il, state, ds);
+            }
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0); // > 0
+            il.Emit(System.Reflection.Emit.OpCodes.Cgt);
+            il.Emit(System.Reflection.Emit.OpCodes.Brfalse, falseBranch);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // 1
+            il.Emit(System.Reflection.Emit.OpCodes.Br, end);
+            il.MarkLabel(falseBranch);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // -1
+            il.Emit(System.Reflection.Emit.OpCodes.Neg);
+            il.MarkLabel(end);
+            return;
+          }
+        case OpCodes.OR: {
+            Label trueBranch = il.DefineLabel();
+            Label end = il.DefineLabel();
+            Label resultBranch = il.DefineLabel();
+            CompileInstructions(il, state, ds);
+            for (int i = 1; i < nArgs; i++) {
+              Label nextArgBranch = il.DefineLabel();
+              // complex definition because of special properties of NaN  
+              il.Emit(System.Reflection.Emit.OpCodes.Dup);
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0); // <= 0        
+              il.Emit(System.Reflection.Emit.OpCodes.Ble, nextArgBranch);
+              il.Emit(System.Reflection.Emit.OpCodes.Br, resultBranch);
+              il.MarkLabel(nextArgBranch);
+              il.Emit(System.Reflection.Emit.OpCodes.Pop);
+              CompileInstructions(il, state, ds);
+            }
+            il.MarkLabel(resultBranch);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0); // > 0
+            il.Emit(System.Reflection.Emit.OpCodes.Cgt);
+            il.Emit(System.Reflection.Emit.OpCodes.Brtrue, trueBranch);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // -1
+            il.Emit(System.Reflection.Emit.OpCodes.Neg);
+            il.Emit(System.Reflection.Emit.OpCodes.Br, end);
+            il.MarkLabel(trueBranch);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // 1
+            il.MarkLabel(end);
+            return;
+          }
+        case OpCodes.NOT: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0); // > 0
+            il.Emit(System.Reflection.Emit.OpCodes.Cgt);
+            il.Emit(System.Reflection.Emit.OpCodes.Conv_R8); // convert to float64
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 2.0); // * 2
+            il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // - 1
+            il.Emit(System.Reflection.Emit.OpCodes.Sub);
+            il.Emit(System.Reflection.Emit.OpCodes.Neg); // * -1
+            return;
+          }
+        case OpCodes.XOR: {
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0);
+            il.Emit(System.Reflection.Emit.OpCodes.Cgt);// > 0
+
+            for (int i = 1; i < nArgs; i++) {
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0);
+              il.Emit(System.Reflection.Emit.OpCodes.Cgt);// > 0
+              il.Emit(System.Reflection.Emit.OpCodes.Xor);
+            }
+            il.Emit(System.Reflection.Emit.OpCodes.Conv_R8); // convert to float64
+
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 2.0); // * 2
+            il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // - 1
+            il.Emit(System.Reflection.Emit.OpCodes.Sub);
+            return;
+          }
+        case OpCodes.GT: {
+            CompileInstructions(il, state, ds);
+            CompileInstructions(il, state, ds);
+
+            il.Emit(System.Reflection.Emit.OpCodes.Cgt); // 1 (>) / 0 (otherwise)
+            il.Emit(System.Reflection.Emit.OpCodes.Conv_R8); // convert to float64
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 2.0); // * 2
+            il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // - 1
+            il.Emit(System.Reflection.Emit.OpCodes.Sub);
+            return;
+          }
+        case OpCodes.LT: {
+            CompileInstructions(il, state, ds);
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Clt);
+            il.Emit(System.Reflection.Emit.OpCodes.Conv_R8); // convert to float64
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 2.0); // * 2
+            il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 1.0); // - 1
+            il.Emit(System.Reflection.Emit.OpCodes.Sub);
+            return;
+          }
+        case OpCodes.TimeLag: {
+            LaggedTreeNode laggedTreeNode = (LaggedTreeNode)currentInstr.dynamicNode;
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // row -= lag
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4, laggedTreeNode.Lag);
+            il.Emit(System.Reflection.Emit.OpCodes.Add);
+            il.Emit(System.Reflection.Emit.OpCodes.Starg, 0);
+            var prevLaggedContext = state.InLaggedContext;
+            state.InLaggedContext = true;
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // row += lag
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4, laggedTreeNode.Lag);
+            il.Emit(System.Reflection.Emit.OpCodes.Sub);
+            il.Emit(System.Reflection.Emit.OpCodes.Starg, 0);
+            state.InLaggedContext = prevLaggedContext;
+            return;
+          }
+        case OpCodes.Integral: {
+            int savedPc = state.ProgramCounter;
+            LaggedTreeNode laggedTreeNode = (LaggedTreeNode)currentInstr.dynamicNode;
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // row -= lag
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4, laggedTreeNode.Lag);
+            il.Emit(System.Reflection.Emit.OpCodes.Add);
+            il.Emit(System.Reflection.Emit.OpCodes.Starg, 0);
+            var prevLaggedContext = state.InLaggedContext;
+            state.InLaggedContext = true;
+            CompileInstructions(il, state, ds);
+            for (int l = laggedTreeNode.Lag; l < 0; l++) {
+              il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // row += lag
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_1);
+              il.Emit(System.Reflection.Emit.OpCodes.Add);
+              il.Emit(System.Reflection.Emit.OpCodes.Starg, 0);
+              state.ProgramCounter = savedPc;
+              CompileInstructions(il, state, ds);
+              il.Emit(System.Reflection.Emit.OpCodes.Add);
+            }
+            state.InLaggedContext = prevLaggedContext;
+            return;
+          }
+
+        //mkommend: derivate calculation taken from: 
+        //http://www.holoborodko.com/pavel/numerical-methods/numerical-derivative/smooth-low-noise-differentiators/
+        //one sided smooth differentiatior, N = 4
+        // y' = 1/8h (f_i + 2f_i-1, -2 f_i-3 - f_i-4)
+        case OpCodes.Derivative: {
+            int savedPc = state.ProgramCounter;
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // row --
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_M1);
+            il.Emit(System.Reflection.Emit.OpCodes.Add);
+            il.Emit(System.Reflection.Emit.OpCodes.Starg, 0);
+            state.ProgramCounter = savedPc;
+            var prevLaggedContext = state.InLaggedContext;
+            state.InLaggedContext = true;
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 2.0); // f_0 + 2 * f_1
+            il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            il.Emit(System.Reflection.Emit.OpCodes.Add);
+
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // row -=2
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_2);
+            il.Emit(System.Reflection.Emit.OpCodes.Sub);
+            il.Emit(System.Reflection.Emit.OpCodes.Starg, 0);
+            state.ProgramCounter = savedPc;
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 2.0); // f_0 + 2 * f_1 - 2 * f_3
+            il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            il.Emit(System.Reflection.Emit.OpCodes.Sub);
+
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // row --
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_M1);
+            il.Emit(System.Reflection.Emit.OpCodes.Add);
+            il.Emit(System.Reflection.Emit.OpCodes.Starg, 0);
+            state.ProgramCounter = savedPc;
+            CompileInstructions(il, state, ds);
+            il.Emit(System.Reflection.Emit.OpCodes.Sub); // f_0 + 2 * f_1 - 2 * f_3 - f_4
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, 8.0); // / 8
+            il.Emit(System.Reflection.Emit.OpCodes.Div);
+
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // row +=4
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_4);
+            il.Emit(System.Reflection.Emit.OpCodes.Add);
+            il.Emit(System.Reflection.Emit.OpCodes.Starg, 0);
+            state.InLaggedContext = prevLaggedContext;
+            return;
+          }
+        case OpCodes.Call: {
+            throw new NotSupportedException(
+              "Automatically defined functions are not supported by the SymbolicDataAnalysisTreeILEmittingInterpreter. Either turn of ADFs or change the interpeter.");
+          }
+        case OpCodes.Arg: {
+            throw new NotSupportedException(
+              "Automatically defined functions are not supported by the SymbolicDataAnalysisTreeILEmittingInterpreter. Either turn of ADFs or change the interpeter.");
+          }
+        case OpCodes.Variable: {
+            VariableTreeNode varNode = (VariableTreeNode)currentInstr.dynamicNode;
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_1); // load columns array
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4, (int)currentInstr.data);
+            // load correct column of the current variable
+            il.Emit(System.Reflection.Emit.OpCodes.Ldelem_Ref);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // rowIndex
+            if (!state.InLaggedContext) {
+              il.Emit(System.Reflection.Emit.OpCodes.Call, listGetValue);
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, varNode.Weight); // load weight
+              il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            } else {
+              var nanResult = il.DefineLabel();
+              var normalResult = il.DefineLabel();
+              il.Emit(System.Reflection.Emit.OpCodes.Dup);
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0);
+              il.Emit(System.Reflection.Emit.OpCodes.Blt, nanResult);
+              il.Emit(System.Reflection.Emit.OpCodes.Dup);
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4, ds.Rows);
+              il.Emit(System.Reflection.Emit.OpCodes.Bge, nanResult);
+              il.Emit(System.Reflection.Emit.OpCodes.Call, listGetValue);
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, varNode.Weight); // load weight
+              il.Emit(System.Reflection.Emit.OpCodes.Mul);
+              il.Emit(System.Reflection.Emit.OpCodes.Br, normalResult);
+              il.MarkLabel(nanResult);
+              il.Emit(System.Reflection.Emit.OpCodes.Pop); // rowIndex
+              il.Emit(System.Reflection.Emit.OpCodes.Pop); // column reference
+              il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, double.NaN);
+              il.MarkLabel(normalResult);
+            }
+            return;
+          }
+        case OpCodes.LagVariable: {
+            var nanResult = il.DefineLabel();
+            var normalResult = il.DefineLabel();
+            LaggedVariableTreeNode varNode = (LaggedVariableTreeNode)currentInstr.dynamicNode;
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_1); // load columns array
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4, (int)currentInstr.data);
+            // load correct column of the current variable
+            il.Emit(System.Reflection.Emit.OpCodes.Ldelem_Ref);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4, varNode.Lag); // lag
+            il.Emit(System.Reflection.Emit.OpCodes.Ldarg_0); // rowIndex
+            il.Emit(System.Reflection.Emit.OpCodes.Add); // actualRowIndex = rowIndex + sampleOffset
+            il.Emit(System.Reflection.Emit.OpCodes.Dup);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4_0);
+            il.Emit(System.Reflection.Emit.OpCodes.Blt, nanResult);
+            il.Emit(System.Reflection.Emit.OpCodes.Dup);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_I4, ds.Rows);
+            il.Emit(System.Reflection.Emit.OpCodes.Bge, nanResult);
+            il.Emit(System.Reflection.Emit.OpCodes.Call, listGetValue);
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, varNode.Weight); // load weight
+            il.Emit(System.Reflection.Emit.OpCodes.Mul);
+            il.Emit(System.Reflection.Emit.OpCodes.Br, normalResult);
+            il.MarkLabel(nanResult);
+            il.Emit(System.Reflection.Emit.OpCodes.Pop); // sample index
+            il.Emit(System.Reflection.Emit.OpCodes.Pop); // column reference
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, double.NaN);
+            il.MarkLabel(normalResult);
+            return;
+          }
+        case OpCodes.Constant: {
+            ConstantTreeNode constNode = (ConstantTreeNode)currentInstr.dynamicNode;
+            il.Emit(System.Reflection.Emit.OpCodes.Ldc_R8, constNode.Value);
+            return;
+          }
+
+        //mkommend: this symbol uses the logistic function f(x) = 1 / (1 + e^(-alpha * x) ) 
+        //to determine the relative amounts of the true and false branch see http://en.wikipedia.org/wiki/Logistic_function
+        case OpCodes.VariableCondition: {
+            throw new NotSupportedException("Interpretation of symbol " + currentInstr.dynamicNode.Symbol.Name +
+                                            " is not supported by the SymbolicDataAnalysisTreeILEmittingInterpreter");
+          }
+        default:
+          throw new NotSupportedException("Interpretation of symbol " + currentInstr.dynamicNode.Symbol.Name +
+                                          " is not supported by the SymbolicDataAnalysisTreeILEmittingInterpreter");
+      }
+    }
+
+    public static double AiryA(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      double ai, aip, bi, bip;
+      alglib.airy(x, out ai, out aip, out bi, out bip);
+      return ai;
+    }
+
+    public static double AiryB(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      double ai, aip, bi, bip;
+      alglib.airy(x, out ai, out aip, out bi, out bip);
+      return bi;
+    }
+    public static double Dawson(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      return alglib.dawsonintegral(x);
+    }
+
+    public static double Gamma(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      return alglib.gammafunction(x);
+    }
+
+    public static double Psi(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      else if (x <= 0 && (Math.Floor(x) - x).IsAlmost(0)) return double.NaN;
+      return alglib.psi(x);
+    }
+
+    public static double ExpIntegralEi(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      return alglib.exponentialintegralei(x);
+    }
+
+    public static double SinIntegral(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      double si, ci;
+      alglib.sinecosineintegrals(x, out si, out ci);
+      return si;
+    }
+
+    public static double CosIntegral(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      double si, ci;
+      alglib.sinecosineintegrals(x, out si, out ci);
+      return ci;
+    }
+
+    public static double HypSinIntegral(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      double shi, chi;
+      alglib.hyperbolicsinecosineintegrals(x, out shi, out chi);
+      return shi;
+    }
+
+    public static double HypCosIntegral(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      double shi, chi;
+      alglib.hyperbolicsinecosineintegrals(x, out shi, out chi);
+      return chi;
+    }
+
+    public static double FresnelCosIntegral(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      double c = 0, s = 0;
+      alglib.fresnelintegral(x, ref c, ref s);
+      return c;
+    }
+
+    public static double FresnelSinIntegral(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      double c = 0, s = 0;
+      alglib.fresnelintegral(x, ref c, ref s);
+      return s;
+    }
+
+    public static double Norm(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      return alglib.normaldistribution(x);
+    }
+
+    public static double Erf(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      return alglib.errorfunction(x);
+    }
+
+    public static double Bessel(double x) {
+      if (double.IsNaN(x)) return double.NaN;
+      return alglib.besseli0(x);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeInterpreter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeInterpreter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeInterpreter.cs	(revision 16337)
@@ -0,0 +1,517 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicDataAnalysisExpressionTreeInterpreter", "Interpreter for symbolic expression trees including automatically defined functions.")]
+  public class SymbolicDataAnalysisExpressionTreeInterpreter : ParameterizedNamedItem,
+    ISymbolicDataAnalysisExpressionTreeInterpreter {
+    private const string CheckExpressionsWithIntervalArithmeticParameterName = "CheckExpressionsWithIntervalArithmetic";
+    private const string CheckExpressionsWithIntervalArithmeticParameterDescription = "Switch that determines if the interpreter checks the validity of expressions with interval arithmetic before evaluating the expression.";
+    private const string EvaluatedSolutionsParameterName = "EvaluatedSolutions";
+
+    public override bool CanChangeName {
+      get { return false; }
+    }
+
+    public override bool CanChangeDescription {
+      get { return false; }
+    }
+
+    #region parameter properties
+    public IFixedValueParameter<BoolValue> CheckExpressionsWithIntervalArithmeticParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[CheckExpressionsWithIntervalArithmeticParameterName]; }
+    }
+
+    public IFixedValueParameter<IntValue> EvaluatedSolutionsParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    public bool CheckExpressionsWithIntervalArithmetic {
+      get { return CheckExpressionsWithIntervalArithmeticParameter.Value.Value; }
+      set { CheckExpressionsWithIntervalArithmeticParameter.Value.Value = value; }
+    }
+
+    public int EvaluatedSolutions {
+      get { return EvaluatedSolutionsParameter.Value.Value; }
+      set { EvaluatedSolutionsParameter.Value.Value = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionTreeInterpreter(bool deserializing) : base(deserializing) { }
+
+    protected SymbolicDataAnalysisExpressionTreeInterpreter(SymbolicDataAnalysisExpressionTreeInterpreter original,
+      Cloner cloner)
+      : base(original, cloner) { }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionTreeInterpreter(this, cloner);
+    }
+
+    public SymbolicDataAnalysisExpressionTreeInterpreter()
+      : base("SymbolicDataAnalysisExpressionTreeInterpreter", "Interpreter for symbolic expression trees including automatically defined functions.") {
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, "Switch that determines if the interpreter checks the validity of expressions with interval arithmetic before evaluating the expression.", new BoolValue(false)));
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+    }
+
+    protected SymbolicDataAnalysisExpressionTreeInterpreter(string name, string description)
+      : base(name, description) {
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, "Switch that determines if the interpreter checks the validity of expressions with interval arithmetic before evaluating the expression.", new BoolValue(false)));
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      var evaluatedSolutions = new IntValue(0);
+      var checkExpressionsWithIntervalArithmetic = new BoolValue(false);
+      if (Parameters.ContainsKey(EvaluatedSolutionsParameterName)) {
+        var evaluatedSolutionsParameter = (IValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName];
+        evaluatedSolutions = evaluatedSolutionsParameter.Value;
+        Parameters.Remove(EvaluatedSolutionsParameterName);
+      }
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", evaluatedSolutions));
+      if (Parameters.ContainsKey(CheckExpressionsWithIntervalArithmeticParameterName)) {
+        var checkExpressionsWithIntervalArithmeticParameter = (IValueParameter<BoolValue>)Parameters[CheckExpressionsWithIntervalArithmeticParameterName];
+        Parameters.Remove(CheckExpressionsWithIntervalArithmeticParameterName);
+        checkExpressionsWithIntervalArithmetic = checkExpressionsWithIntervalArithmeticParameter.Value;
+      }
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, CheckExpressionsWithIntervalArithmeticParameterDescription, checkExpressionsWithIntervalArithmetic));
+    }
+
+    #region IStatefulItem
+    public void InitializeState() {
+      EvaluatedSolutions = 0;
+    }
+
+    public void ClearState() { }
+    #endregion
+
+    private readonly object syncRoot = new object();
+    public IEnumerable<double> GetSymbolicExpressionTreeValues(ISymbolicExpressionTree tree, IDataset dataset,
+      IEnumerable<int> rows) {
+      if (CheckExpressionsWithIntervalArithmetic) {
+        throw new NotSupportedException("Interval arithmetic is not yet supported in the symbolic data analysis interpreter.");
+      }
+
+      lock (syncRoot) {
+        EvaluatedSolutions++; // increment the evaluated solutions counter
+      }
+      var state = PrepareInterpreterState(tree, dataset);
+
+      foreach (var rowEnum in rows) {
+        int row = rowEnum;
+        yield return Evaluate(dataset, ref row, state);
+        state.Reset();
+      }
+    }
+
+    private static InterpreterState PrepareInterpreterState(ISymbolicExpressionTree tree, IDataset dataset) {
+      Instruction[] code = SymbolicExpressionTreeCompiler.Compile(tree, OpCodes.MapSymbolToOpCode);
+      int necessaryArgStackSize = 0;
+      foreach (Instruction instr in code) {
+        if (instr.opCode == OpCodes.Variable) {
+          var variableTreeNode = (VariableTreeNode)instr.dynamicNode;
+          instr.data = dataset.GetReadOnlyDoubleValues(variableTreeNode.VariableName);
+        } else if (instr.opCode == OpCodes.FactorVariable) {
+          var factorTreeNode = instr.dynamicNode as FactorVariableTreeNode;
+          instr.data = dataset.GetReadOnlyStringValues(factorTreeNode.VariableName);
+        } else if (instr.opCode == OpCodes.BinaryFactorVariable) {
+          var factorTreeNode = instr.dynamicNode as BinaryFactorVariableTreeNode;
+          instr.data = dataset.GetReadOnlyStringValues(factorTreeNode.VariableName);
+        } else if (instr.opCode == OpCodes.LagVariable) {
+          var laggedVariableTreeNode = (LaggedVariableTreeNode)instr.dynamicNode;
+          instr.data = dataset.GetReadOnlyDoubleValues(laggedVariableTreeNode.VariableName);
+        } else if (instr.opCode == OpCodes.VariableCondition) {
+          var variableConditionTreeNode = (VariableConditionTreeNode)instr.dynamicNode;
+          instr.data = dataset.GetReadOnlyDoubleValues(variableConditionTreeNode.VariableName);
+        } else if (instr.opCode == OpCodes.Call) {
+          necessaryArgStackSize += instr.nArguments + 1;
+        }
+      }
+      return new InterpreterState(code, necessaryArgStackSize);
+    }
+
+    public virtual double Evaluate(IDataset dataset, ref int row, InterpreterState state) {
+      Instruction currentInstr = state.NextInstruction();
+      switch (currentInstr.opCode) {
+        case OpCodes.Add: {
+            double s = Evaluate(dataset, ref row, state);
+            for (int i = 1; i < currentInstr.nArguments; i++) {
+              s += Evaluate(dataset, ref row, state);
+            }
+            return s;
+          }
+        case OpCodes.Sub: {
+            double s = Evaluate(dataset, ref row, state);
+            for (int i = 1; i < currentInstr.nArguments; i++) {
+              s -= Evaluate(dataset, ref row, state);
+            }
+            if (currentInstr.nArguments == 1) { s = -s; }
+            return s;
+          }
+        case OpCodes.Mul: {
+            double p = Evaluate(dataset, ref row, state);
+            for (int i = 1; i < currentInstr.nArguments; i++) {
+              p *= Evaluate(dataset, ref row, state);
+            }
+            return p;
+          }
+        case OpCodes.Div: {
+            double p = Evaluate(dataset, ref row, state);
+            for (int i = 1; i < currentInstr.nArguments; i++) {
+              p /= Evaluate(dataset, ref row, state);
+            }
+            if (currentInstr.nArguments == 1) { p = 1.0 / p; }
+            return p;
+          }
+        case OpCodes.Average: {
+            double sum = Evaluate(dataset, ref row, state);
+            for (int i = 1; i < currentInstr.nArguments; i++) {
+              sum += Evaluate(dataset, ref row, state);
+            }
+            return sum / currentInstr.nArguments;
+          }
+        case OpCodes.Cos: {
+            return Math.Cos(Evaluate(dataset, ref row, state));
+          }
+        case OpCodes.Sin: {
+            return Math.Sin(Evaluate(dataset, ref row, state));
+          }
+        case OpCodes.Tan: {
+            return Math.Tan(Evaluate(dataset, ref row, state));
+          }
+        case OpCodes.Square: {
+            return Math.Pow(Evaluate(dataset, ref row, state), 2);
+          }
+        case OpCodes.Power: {
+            double x = Evaluate(dataset, ref row, state);
+            double y = Math.Round(Evaluate(dataset, ref row, state));
+            return Math.Pow(x, y);
+          }
+        case OpCodes.SquareRoot: {
+            return Math.Sqrt(Evaluate(dataset, ref row, state));
+          }
+        case OpCodes.Root: {
+            double x = Evaluate(dataset, ref row, state);
+            double y = Math.Round(Evaluate(dataset, ref row, state));
+            return Math.Pow(x, 1 / y);
+          }
+        case OpCodes.Exp: {
+            return Math.Exp(Evaluate(dataset, ref row, state));
+          }
+        case OpCodes.Log: {
+            return Math.Log(Evaluate(dataset, ref row, state));
+          }
+        case OpCodes.Gamma: {
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) { return double.NaN; } else { return alglib.gammafunction(x); }
+          }
+        case OpCodes.Psi: {
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else if (x <= 0 && (Math.Floor(x) - x).IsAlmost(0)) return double.NaN;
+            return alglib.psi(x);
+          }
+        case OpCodes.Dawson: {
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) { return double.NaN; }
+            return alglib.dawsonintegral(x);
+          }
+        case OpCodes.ExponentialIntegralEi: {
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) { return double.NaN; }
+            return alglib.exponentialintegralei(x);
+          }
+        case OpCodes.SineIntegral: {
+            double si, ci;
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else {
+              alglib.sinecosineintegrals(x, out si, out ci);
+              return si;
+            }
+          }
+        case OpCodes.CosineIntegral: {
+            double si, ci;
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else {
+              alglib.sinecosineintegrals(x, out si, out ci);
+              return ci;
+            }
+          }
+        case OpCodes.HyperbolicSineIntegral: {
+            double shi, chi;
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else {
+              alglib.hyperbolicsinecosineintegrals(x, out shi, out chi);
+              return shi;
+            }
+          }
+        case OpCodes.HyperbolicCosineIntegral: {
+            double shi, chi;
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else {
+              alglib.hyperbolicsinecosineintegrals(x, out shi, out chi);
+              return chi;
+            }
+          }
+        case OpCodes.FresnelCosineIntegral: {
+            double c = 0, s = 0;
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else {
+              alglib.fresnelintegral(x, ref c, ref s);
+              return c;
+            }
+          }
+        case OpCodes.FresnelSineIntegral: {
+            double c = 0, s = 0;
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else {
+              alglib.fresnelintegral(x, ref c, ref s);
+              return s;
+            }
+          }
+        case OpCodes.AiryA: {
+            double ai, aip, bi, bip;
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else {
+              alglib.airy(x, out ai, out aip, out bi, out bip);
+              return ai;
+            }
+          }
+        case OpCodes.AiryB: {
+            double ai, aip, bi, bip;
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else {
+              alglib.airy(x, out ai, out aip, out bi, out bip);
+              return bi;
+            }
+          }
+        case OpCodes.Norm: {
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else return alglib.normaldistribution(x);
+          }
+        case OpCodes.Erf: {
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else return alglib.errorfunction(x);
+          }
+        case OpCodes.Bessel: {
+            var x = Evaluate(dataset, ref row, state);
+            if (double.IsNaN(x)) return double.NaN;
+            else return alglib.besseli0(x);
+          }
+        case OpCodes.IfThenElse: {
+            double condition = Evaluate(dataset, ref row, state);
+            double result;
+            if (condition > 0.0) {
+              result = Evaluate(dataset, ref row, state); state.SkipInstructions();
+            } else {
+              state.SkipInstructions(); result = Evaluate(dataset, ref row, state);
+            }
+            return result;
+          }
+        case OpCodes.AND: {
+            double result = Evaluate(dataset, ref row, state);
+            for (int i = 1; i < currentInstr.nArguments; i++) {
+              if (result > 0.0) result = Evaluate(dataset, ref row, state);
+              else {
+                state.SkipInstructions();
+              }
+            }
+            return result > 0.0 ? 1.0 : -1.0;
+          }
+        case OpCodes.OR: {
+            double result = Evaluate(dataset, ref row, state);
+            for (int i = 1; i < currentInstr.nArguments; i++) {
+              if (result <= 0.0) result = Evaluate(dataset, ref row, state);
+              else {
+                state.SkipInstructions();
+              }
+            }
+            return result > 0.0 ? 1.0 : -1.0;
+          }
+        case OpCodes.NOT: {
+            return Evaluate(dataset, ref row, state) > 0.0 ? -1.0 : 1.0;
+          }
+        case OpCodes.XOR: {
+            //mkommend: XOR on multiple inputs is defined as true if the number of positive signals is odd
+            // this is equal to a consecutive execution of binary XOR operations.
+            int positiveSignals = 0;
+            for (int i = 0; i < currentInstr.nArguments; i++) {
+              if (Evaluate(dataset, ref row, state) > 0.0) { positiveSignals++; }
+            }
+            return positiveSignals % 2 != 0 ? 1.0 : -1.0;
+          }
+        case OpCodes.GT: {
+            double x = Evaluate(dataset, ref row, state);
+            double y = Evaluate(dataset, ref row, state);
+            if (x > y) { return 1.0; } else { return -1.0; }
+          }
+        case OpCodes.LT: {
+            double x = Evaluate(dataset, ref row, state);
+            double y = Evaluate(dataset, ref row, state);
+            if (x < y) { return 1.0; } else { return -1.0; }
+          }
+        case OpCodes.TimeLag: {
+            var timeLagTreeNode = (LaggedTreeNode)currentInstr.dynamicNode;
+            row += timeLagTreeNode.Lag;
+            double result = Evaluate(dataset, ref row, state);
+            row -= timeLagTreeNode.Lag;
+            return result;
+          }
+        case OpCodes.Integral: {
+            int savedPc = state.ProgramCounter;
+            var timeLagTreeNode = (LaggedTreeNode)currentInstr.dynamicNode;
+            double sum = 0.0;
+            for (int i = 0; i < Math.Abs(timeLagTreeNode.Lag); i++) {
+              row += Math.Sign(timeLagTreeNode.Lag);
+              sum += Evaluate(dataset, ref row, state);
+              state.ProgramCounter = savedPc;
+            }
+            row -= timeLagTreeNode.Lag;
+            sum += Evaluate(dataset, ref row, state);
+            return sum;
+          }
+
+        //mkommend: derivate calculation taken from: 
+        //http://www.holoborodko.com/pavel/numerical-methods/numerical-derivative/smooth-low-noise-differentiators/
+        //one sided smooth differentiatior, N = 4
+        // y' = 1/8h (f_i + 2f_i-1, -2 f_i-3 - f_i-4)
+        case OpCodes.Derivative: {
+            int savedPc = state.ProgramCounter;
+            double f_0 = Evaluate(dataset, ref row, state); row--;
+            state.ProgramCounter = savedPc;
+            double f_1 = Evaluate(dataset, ref row, state); row -= 2;
+            state.ProgramCounter = savedPc;
+            double f_3 = Evaluate(dataset, ref row, state); row--;
+            state.ProgramCounter = savedPc;
+            double f_4 = Evaluate(dataset, ref row, state);
+            row += 4;
+
+            return (f_0 + 2 * f_1 - 2 * f_3 - f_4) / 8; // h = 1
+          }
+        case OpCodes.Call: {
+            // evaluate sub-trees
+            double[] argValues = new double[currentInstr.nArguments];
+            for (int i = 0; i < currentInstr.nArguments; i++) {
+              argValues[i] = Evaluate(dataset, ref row, state);
+            }
+            // push on argument values on stack 
+            state.CreateStackFrame(argValues);
+
+            // save the pc
+            int savedPc = state.ProgramCounter;
+            // set pc to start of function  
+            state.ProgramCounter = (ushort)currentInstr.data;
+            // evaluate the function
+            double v = Evaluate(dataset, ref row, state);
+
+            // delete the stack frame
+            state.RemoveStackFrame();
+
+            // restore the pc => evaluation will continue at point after my subtrees  
+            state.ProgramCounter = savedPc;
+            return v;
+          }
+        case OpCodes.Arg: {
+            return state.GetStackFrameValue((ushort)currentInstr.data);
+          }
+        case OpCodes.Variable: {
+            if (row < 0 || row >= dataset.Rows) return double.NaN;
+            var variableTreeNode = (VariableTreeNode)currentInstr.dynamicNode;
+            return ((IList<double>)currentInstr.data)[row] * variableTreeNode.Weight;
+          }
+        case OpCodes.BinaryFactorVariable: {
+            if (row < 0 || row >= dataset.Rows) return double.NaN;
+            var factorVarTreeNode = currentInstr.dynamicNode as BinaryFactorVariableTreeNode;
+            return ((IList<string>)currentInstr.data)[row] == factorVarTreeNode.VariableValue ? factorVarTreeNode.Weight : 0;
+          }
+        case OpCodes.FactorVariable: {
+            if (row < 0 || row >= dataset.Rows) return double.NaN;
+            var factorVarTreeNode = currentInstr.dynamicNode as FactorVariableTreeNode;
+            return factorVarTreeNode.GetValue(((IList<string>)currentInstr.data)[row]);
+          }
+        case OpCodes.LagVariable: {
+            var laggedVariableTreeNode = (LaggedVariableTreeNode)currentInstr.dynamicNode;
+            int actualRow = row + laggedVariableTreeNode.Lag;
+            if (actualRow < 0 || actualRow >= dataset.Rows) { return double.NaN; }
+            return ((IList<double>)currentInstr.data)[actualRow] * laggedVariableTreeNode.Weight;
+          }
+        case OpCodes.Constant: {
+            var constTreeNode = (ConstantTreeNode)currentInstr.dynamicNode;
+            return constTreeNode.Value;
+          }
+
+        //mkommend: this symbol uses the logistic function f(x) = 1 / (1 + e^(-alpha * x) ) 
+        //to determine the relative amounts of the true and false branch see http://en.wikipedia.org/wiki/Logistic_function
+        case OpCodes.VariableCondition: {
+            if (row < 0 || row >= dataset.Rows) return double.NaN;
+            var variableConditionTreeNode = (VariableConditionTreeNode)currentInstr.dynamicNode;
+            if (!variableConditionTreeNode.Symbol.IgnoreSlope) {
+              double variableValue = ((IList<double>)currentInstr.data)[row];
+              double x = variableValue - variableConditionTreeNode.Threshold;
+              double p = 1 / (1 + Math.Exp(-variableConditionTreeNode.Slope * x));
+
+              double trueBranch = Evaluate(dataset, ref row, state);
+              double falseBranch = Evaluate(dataset, ref row, state);
+
+              return trueBranch * p + falseBranch * (1 - p);
+            } else {
+              // strict threshold
+              double variableValue = ((IList<double>)currentInstr.data)[row];
+              if (variableValue <= variableConditionTreeNode.Threshold) {
+                var left = Evaluate(dataset, ref row, state);
+                state.SkipInstructions();
+                return left;
+              } else {
+                state.SkipInstructions();
+                return Evaluate(dataset, ref row, state);
+              }
+            }
+          }
+        default:
+          throw new NotSupportedException();
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeLinearInterpreter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeLinearInterpreter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeLinearInterpreter.cs	(revision 16337)
@@ -0,0 +1,452 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicDataAnalysisExpressionTreeLinearInterpreter", "Fast linear (non-recursive) interpreter for symbolic expression trees. Does not support ADFs.")]
+  public sealed class SymbolicDataAnalysisExpressionTreeLinearInterpreter : ParameterizedNamedItem, ISymbolicDataAnalysisExpressionTreeInterpreter {
+    private const string CheckExpressionsWithIntervalArithmeticParameterName = "CheckExpressionsWithIntervalArithmetic";
+    private const string CheckExpressionsWithIntervalArithmeticParameterDescription = "Switch that determines if the interpreter checks the validity of expressions with interval arithmetic before evaluating the expression.";
+    private const string EvaluatedSolutionsParameterName = "EvaluatedSolutions";
+
+    private readonly SymbolicDataAnalysisExpressionTreeInterpreter interpreter;
+
+    public override bool CanChangeName {
+      get { return false; }
+    }
+
+    public override bool CanChangeDescription {
+      get { return false; }
+    }
+
+    #region parameter properties
+    public IFixedValueParameter<BoolValue> CheckExpressionsWithIntervalArithmeticParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[CheckExpressionsWithIntervalArithmeticParameterName]; }
+    }
+
+    public IFixedValueParameter<IntValue> EvaluatedSolutionsParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    public bool CheckExpressionsWithIntervalArithmetic {
+      get { return CheckExpressionsWithIntervalArithmeticParameter.Value.Value; }
+      set { CheckExpressionsWithIntervalArithmeticParameter.Value.Value = value; }
+    }
+    public int EvaluatedSolutions {
+      get { return EvaluatedSolutionsParameter.Value.Value; }
+      set { EvaluatedSolutionsParameter.Value.Value = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    private SymbolicDataAnalysisExpressionTreeLinearInterpreter(bool deserializing)
+      : base(deserializing) {
+      interpreter = new SymbolicDataAnalysisExpressionTreeInterpreter();
+    }
+
+    private SymbolicDataAnalysisExpressionTreeLinearInterpreter(SymbolicDataAnalysisExpressionTreeLinearInterpreter original, Cloner cloner)
+      : base(original, cloner) {
+      interpreter = cloner.Clone(original.interpreter);
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionTreeLinearInterpreter(this, cloner);
+    }
+
+    public SymbolicDataAnalysisExpressionTreeLinearInterpreter()
+      : base("SymbolicDataAnalysisExpressionTreeLinearInterpreter", "Linear (non-recursive) interpreter for symbolic expression trees (does not support ADFs).") {
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, CheckExpressionsWithIntervalArithmeticParameterDescription, new BoolValue(false)));
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+      interpreter = new SymbolicDataAnalysisExpressionTreeInterpreter();
+    }
+
+    public SymbolicDataAnalysisExpressionTreeLinearInterpreter(string name, string description)
+      : base(name, description) {
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, CheckExpressionsWithIntervalArithmeticParameterDescription, new BoolValue(false)));
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+      interpreter = new SymbolicDataAnalysisExpressionTreeInterpreter();
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      var evaluatedSolutions = new IntValue(0);
+      var checkExpressionsWithIntervalArithmetic = new BoolValue(false);
+      if (Parameters.ContainsKey(EvaluatedSolutionsParameterName)) {
+        var evaluatedSolutionsParameter = (IValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName];
+        evaluatedSolutions = evaluatedSolutionsParameter.Value;
+        Parameters.Remove(EvaluatedSolutionsParameterName);
+      }
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", evaluatedSolutions));
+      if (Parameters.ContainsKey(CheckExpressionsWithIntervalArithmeticParameterName)) {
+        var checkExpressionsWithIntervalArithmeticParameter = (IValueParameter<BoolValue>)Parameters[CheckExpressionsWithIntervalArithmeticParameterName];
+        Parameters.Remove(CheckExpressionsWithIntervalArithmeticParameterName);
+        checkExpressionsWithIntervalArithmetic = checkExpressionsWithIntervalArithmeticParameter.Value;
+      }
+      Parameters.Add(new FixedValueParameter<BoolValue>(CheckExpressionsWithIntervalArithmeticParameterName, CheckExpressionsWithIntervalArithmeticParameterDescription, checkExpressionsWithIntervalArithmetic));
+    }
+
+    #region IStatefulItem
+    public void InitializeState() {
+      EvaluatedSolutions = 0;
+    }
+
+    public void ClearState() { }
+    #endregion
+
+    private readonly object syncRoot = new object();
+    public IEnumerable<double> GetSymbolicExpressionTreeValues(ISymbolicExpressionTree tree, IDataset dataset, IEnumerable<int> rows) {
+      if (!rows.Any()) return Enumerable.Empty<double>();
+      if (CheckExpressionsWithIntervalArithmetic)
+        throw new NotSupportedException("Interval arithmetic is not yet supported in the symbolic data analysis interpreter.");
+
+      lock (syncRoot) {
+        EvaluatedSolutions++; // increment the evaluated solutions counter
+      }
+
+      var code = SymbolicExpressionTreeLinearCompiler.Compile(tree, OpCodes.MapSymbolToOpCode);
+      PrepareInstructions(code, dataset);
+      return rows.Select(row => Evaluate(dataset, row, code));
+    }
+
+    private double Evaluate(IDataset dataset, int row, LinearInstruction[] code) {
+      for (int i = code.Length - 1; i >= 0; --i) {
+        if (code[i].skip) continue;
+        #region opcode if
+        var instr = code[i];
+        if (instr.opCode == OpCodes.Variable) {
+          if (row < 0 || row >= dataset.Rows) instr.value = double.NaN;
+          else {
+            var variableTreeNode = (VariableTreeNode)instr.dynamicNode;
+            instr.value = ((IList<double>)instr.data)[row] * variableTreeNode.Weight;
+          }
+        } else if (instr.opCode == OpCodes.BinaryFactorVariable) {
+          if (row < 0 || row >= dataset.Rows) instr.value = double.NaN;
+          else {
+            var factorTreeNode = instr.dynamicNode as BinaryFactorVariableTreeNode;
+            instr.value = ((IList<string>)instr.data)[row] == factorTreeNode.VariableValue ? factorTreeNode.Weight : 0;
+          }
+        } else if (instr.opCode == OpCodes.FactorVariable) {
+          if (row < 0 || row >= dataset.Rows) instr.value = double.NaN;
+          else {
+            var factorTreeNode = instr.dynamicNode as FactorVariableTreeNode;
+            instr.value = factorTreeNode.GetValue(((IList<string>)instr.data)[row]);
+          }
+        } else if (instr.opCode == OpCodes.LagVariable) {
+          var laggedVariableTreeNode = (LaggedVariableTreeNode)instr.dynamicNode;
+          int actualRow = row + laggedVariableTreeNode.Lag;
+          if (actualRow < 0 || actualRow >= dataset.Rows)
+            instr.value = double.NaN;
+          else
+            instr.value = ((IList<double>)instr.data)[actualRow] * laggedVariableTreeNode.Weight;
+        } else if (instr.opCode == OpCodes.VariableCondition) {
+          if (row < 0 || row >= dataset.Rows) instr.value = double.NaN;
+          var variableConditionTreeNode = (VariableConditionTreeNode)instr.dynamicNode;
+          if (!variableConditionTreeNode.Symbol.IgnoreSlope) {
+            double variableValue = ((IList<double>)instr.data)[row];
+            double x = variableValue - variableConditionTreeNode.Threshold;
+            double p = 1 / (1 + Math.Exp(-variableConditionTreeNode.Slope * x));
+
+            double trueBranch = code[instr.childIndex].value;
+            double falseBranch = code[instr.childIndex + 1].value;
+
+            instr.value = trueBranch * p + falseBranch * (1 - p);
+          } else {
+            double variableValue = ((IList<double>)instr.data)[row];
+            if (variableValue <= variableConditionTreeNode.Threshold) {
+              instr.value = code[instr.childIndex].value;
+            } else {
+              instr.value = code[instr.childIndex + 1].value;
+            }
+          }
+        } else if (instr.opCode == OpCodes.Add) {
+          double s = code[instr.childIndex].value;
+          for (int j = 1; j != instr.nArguments; ++j) {
+            s += code[instr.childIndex + j].value;
+          }
+          instr.value = s;
+        } else if (instr.opCode == OpCodes.Sub) {
+          double s = code[instr.childIndex].value;
+          for (int j = 1; j != instr.nArguments; ++j) {
+            s -= code[instr.childIndex + j].value;
+          }
+          if (instr.nArguments == 1) s = -s;
+          instr.value = s;
+        } else if (instr.opCode == OpCodes.Mul) {
+          double p = code[instr.childIndex].value;
+          for (int j = 1; j != instr.nArguments; ++j) {
+            p *= code[instr.childIndex + j].value;
+          }
+          instr.value = p;
+        } else if (instr.opCode == OpCodes.Div) {
+          double p = code[instr.childIndex].value;
+          for (int j = 1; j != instr.nArguments; ++j) {
+            p /= code[instr.childIndex + j].value;
+          }
+          if (instr.nArguments == 1) p = 1.0 / p;
+          instr.value = p;
+        } else if (instr.opCode == OpCodes.Average) {
+          double s = code[instr.childIndex].value;
+          for (int j = 1; j != instr.nArguments; ++j) {
+            s += code[instr.childIndex + j].value;
+          }
+          instr.value = s / instr.nArguments;
+        } else if (instr.opCode == OpCodes.Cos) {
+          instr.value = Math.Cos(code[instr.childIndex].value);
+        } else if (instr.opCode == OpCodes.Sin) {
+          instr.value = Math.Sin(code[instr.childIndex].value);
+        } else if (instr.opCode == OpCodes.Tan) {
+          instr.value = Math.Tan(code[instr.childIndex].value);
+        } else if (instr.opCode == OpCodes.Square) {
+          instr.value = Math.Pow(code[instr.childIndex].value, 2);
+        } else if (instr.opCode == OpCodes.Power) {
+          double x = code[instr.childIndex].value;
+          double y = Math.Round(code[instr.childIndex + 1].value);
+          instr.value = Math.Pow(x, y);
+        } else if (instr.opCode == OpCodes.SquareRoot) {
+          instr.value = Math.Sqrt(code[instr.childIndex].value);
+        } else if (instr.opCode == OpCodes.Root) {
+          double x = code[instr.childIndex].value;
+          double y = Math.Round(code[instr.childIndex + 1].value);
+          instr.value = Math.Pow(x, 1 / y);
+        } else if (instr.opCode == OpCodes.Exp) {
+          instr.value = Math.Exp(code[instr.childIndex].value);
+        } else if (instr.opCode == OpCodes.Log) {
+          instr.value = Math.Log(code[instr.childIndex].value);
+        } else if (instr.opCode == OpCodes.Gamma) {
+          var x = code[instr.childIndex].value;
+          instr.value = double.IsNaN(x) ? double.NaN : alglib.gammafunction(x);
+        } else if (instr.opCode == OpCodes.Psi) {
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else if (x <= 0 && (Math.Floor(x) - x).IsAlmost(0)) instr.value = double.NaN;
+          else instr.value = alglib.psi(x);
+        } else if (instr.opCode == OpCodes.Dawson) {
+          var x = code[instr.childIndex].value;
+          instr.value = double.IsNaN(x) ? double.NaN : alglib.dawsonintegral(x);
+        } else if (instr.opCode == OpCodes.ExponentialIntegralEi) {
+          var x = code[instr.childIndex].value;
+          instr.value = double.IsNaN(x) ? double.NaN : alglib.exponentialintegralei(x);
+        } else if (instr.opCode == OpCodes.SineIntegral) {
+          double si, ci;
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else {
+            alglib.sinecosineintegrals(x, out si, out ci);
+            instr.value = si;
+          }
+        } else if (instr.opCode == OpCodes.CosineIntegral) {
+          double si, ci;
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else {
+            alglib.sinecosineintegrals(x, out si, out ci);
+            instr.value = ci;
+          }
+        } else if (instr.opCode == OpCodes.HyperbolicSineIntegral) {
+          double shi, chi;
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else {
+            alglib.hyperbolicsinecosineintegrals(x, out shi, out chi);
+            instr.value = shi;
+          }
+        } else if (instr.opCode == OpCodes.HyperbolicCosineIntegral) {
+          double shi, chi;
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else {
+            alglib.hyperbolicsinecosineintegrals(x, out shi, out chi);
+            instr.value = chi;
+          }
+        } else if (instr.opCode == OpCodes.FresnelCosineIntegral) {
+          double c = 0, s = 0;
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else {
+            alglib.fresnelintegral(x, ref c, ref s);
+            instr.value = c;
+          }
+        } else if (instr.opCode == OpCodes.FresnelSineIntegral) {
+          double c = 0, s = 0;
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else {
+            alglib.fresnelintegral(x, ref c, ref s);
+            instr.value = s;
+          }
+        } else if (instr.opCode == OpCodes.AiryA) {
+          double ai, aip, bi, bip;
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else {
+            alglib.airy(x, out ai, out aip, out bi, out bip);
+            instr.value = ai;
+          }
+        } else if (instr.opCode == OpCodes.AiryB) {
+          double ai, aip, bi, bip;
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else {
+            alglib.airy(x, out ai, out aip, out bi, out bip);
+            instr.value = bi;
+          }
+        } else if (instr.opCode == OpCodes.Norm) {
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else instr.value = alglib.normaldistribution(x);
+        } else if (instr.opCode == OpCodes.Erf) {
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else instr.value = alglib.errorfunction(x);
+        } else if (instr.opCode == OpCodes.Bessel) {
+          var x = code[instr.childIndex].value;
+          if (double.IsNaN(x)) instr.value = double.NaN;
+          else instr.value = alglib.besseli0(x);
+        } else if (instr.opCode == OpCodes.IfThenElse) {
+          double condition = code[instr.childIndex].value;
+          double result;
+          if (condition > 0.0) {
+            result = code[instr.childIndex + 1].value;
+          } else {
+            result = code[instr.childIndex + 2].value;
+          }
+          instr.value = result;
+        } else if (instr.opCode == OpCodes.AND) {
+          double result = code[instr.childIndex].value;
+          for (int j = 1; j < instr.nArguments; j++) {
+            if (result > 0.0) result = code[instr.childIndex + j].value;
+            else break;
+          }
+          instr.value = result > 0.0 ? 1.0 : -1.0;
+        } else if (instr.opCode == OpCodes.OR) {
+          double result = code[instr.childIndex].value;
+          for (int j = 1; j < instr.nArguments; j++) {
+            if (result <= 0.0) result = code[instr.childIndex + j].value;
+            else break;
+          }
+          instr.value = result > 0.0 ? 1.0 : -1.0;
+        } else if (instr.opCode == OpCodes.NOT) {
+          instr.value = code[instr.childIndex].value > 0.0 ? -1.0 : 1.0;
+        } else if (instr.opCode == OpCodes.XOR) {
+          int positiveSignals = 0;
+          for (int j = 0; j < instr.nArguments; j++) {
+            if (code[instr.childIndex + j].value > 0.0) positiveSignals++;
+          }
+          instr.value = positiveSignals % 2 != 0 ? 1.0 : -1.0;
+        } else if (instr.opCode == OpCodes.GT) {
+          double x = code[instr.childIndex].value;
+          double y = code[instr.childIndex + 1].value;
+          instr.value = x > y ? 1.0 : -1.0;
+        } else if (instr.opCode == OpCodes.LT) {
+          double x = code[instr.childIndex].value;
+          double y = code[instr.childIndex + 1].value;
+          instr.value = x < y ? 1.0 : -1.0;
+        } else if (instr.opCode == OpCodes.TimeLag || instr.opCode == OpCodes.Derivative || instr.opCode == OpCodes.Integral) {
+          var state = (InterpreterState)instr.data;
+          state.Reset();
+          instr.value = interpreter.Evaluate(dataset, ref row, state);
+        } else {
+          var errorText = string.Format("The {0} symbol is not supported by the linear interpreter. To support this symbol, please use the SymbolicDataAnalysisExpressionTreeInterpreter.", instr.dynamicNode.Symbol.Name);
+          throw new NotSupportedException(errorText);
+        }
+        #endregion
+      }
+      return code[0].value;
+    }
+
+    private static LinearInstruction[] GetPrefixSequence(LinearInstruction[] code, int startIndex) {
+      var s = new Stack<int>();
+      var list = new List<LinearInstruction>();
+      s.Push(startIndex);
+      while (s.Any()) {
+        int i = s.Pop();
+        var instr = code[i];
+        // push instructions in reverse execution order
+        for (int j = instr.nArguments - 1; j >= 0; j--) s.Push(instr.childIndex + j);
+        list.Add(instr);
+      }
+      return list.ToArray();
+    }
+
+    public static void PrepareInstructions(LinearInstruction[] code, IDataset dataset) {
+      for (int i = 0; i != code.Length; ++i) {
+        var instr = code[i];
+        #region opcode switch
+        switch (instr.opCode) {
+          case OpCodes.Constant: {
+              var constTreeNode = (ConstantTreeNode)instr.dynamicNode;
+              instr.value = constTreeNode.Value;
+              instr.skip = true; // the value is already set so this instruction should be skipped in the evaluation phase
+            }
+            break;
+          case OpCodes.Variable: {
+              var variableTreeNode = (VariableTreeNode)instr.dynamicNode;
+              instr.data = dataset.GetReadOnlyDoubleValues(variableTreeNode.VariableName);
+            }
+            break;
+          case OpCodes.BinaryFactorVariable: {
+              var factorVariableTreeNode = instr.dynamicNode as BinaryFactorVariableTreeNode;
+              instr.data = dataset.GetReadOnlyStringValues(factorVariableTreeNode.VariableName);
+            }
+            break;
+          case OpCodes.FactorVariable: {
+              var factorVariableTreeNode = instr.dynamicNode as FactorVariableTreeNode;
+              instr.data = dataset.GetReadOnlyStringValues(factorVariableTreeNode.VariableName);
+            }
+            break;
+          case OpCodes.LagVariable: {
+              var laggedVariableTreeNode = (LaggedVariableTreeNode)instr.dynamicNode;
+              instr.data = dataset.GetReadOnlyDoubleValues(laggedVariableTreeNode.VariableName);
+            }
+            break;
+          case OpCodes.VariableCondition: {
+              var variableConditionTreeNode = (VariableConditionTreeNode)instr.dynamicNode;
+              instr.data = dataset.GetReadOnlyDoubleValues(variableConditionTreeNode.VariableName);
+            }
+            break;
+          case OpCodes.TimeLag:
+          case OpCodes.Integral:
+          case OpCodes.Derivative: {
+              var seq = GetPrefixSequence(code, i);
+              var interpreterState = new InterpreterState(seq, 0);
+              instr.data = interpreterState;
+              for (int j = 1; j != seq.Length; ++j)
+                seq[j].skip = true;
+              break;
+            }
+        }
+        #endregion
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeNativeInterpreter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeNativeInterpreter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Interpreter/SymbolicDataAnalysisExpressionTreeNativeInterpreter.cs	(revision 16337)
@@ -0,0 +1,140 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicDataAnalysisExpressionTreeNativeInterpreter", "An interpreter that wraps a native dll")]
+  public class SymbolicDataAnalysisExpressionTreeNativeInterpreter : ParameterizedNamedItem, ISymbolicDataAnalysisExpressionTreeInterpreter {
+    private const string EvaluatedSolutionsParameterName = "EvaluatedSolutions";
+
+    #region parameters
+    public IFixedValueParameter<IntValue> EvaluatedSolutionsParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[EvaluatedSolutionsParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    public int EvaluatedSolutions {
+      get { return EvaluatedSolutionsParameter.Value.Value; }
+      set { EvaluatedSolutionsParameter.Value.Value = value; }
+    }
+    #endregion
+
+    public void ClearState() { }
+
+    public SymbolicDataAnalysisExpressionTreeNativeInterpreter() {
+      Parameters.Add(new FixedValueParameter<IntValue>(EvaluatedSolutionsParameterName, "A counter for the total number of solutions the interpreter has evaluated", new IntValue(0)));
+    }
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionTreeNativeInterpreter(bool deserializing) : base(deserializing) { }
+
+
+    protected SymbolicDataAnalysisExpressionTreeNativeInterpreter(SymbolicDataAnalysisExpressionTreeNativeInterpreter original, Cloner cloner) : base(original, cloner) {
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionTreeNativeInterpreter(this, cloner);
+    }
+
+    private NativeInstruction[] Compile(ISymbolicExpressionTree tree, Func<ISymbolicExpressionTreeNode, byte> opCodeMapper) {
+      var root = tree.Root.GetSubtree(0).GetSubtree(0);
+      var code = new NativeInstruction[root.GetLength()];
+      if (root.SubtreeCount > ushort.MaxValue) throw new ArgumentException("Number of subtrees is too big (>65.535)");
+      code[0] = new NativeInstruction { narg = (ushort)root.SubtreeCount, opcode = opCodeMapper(root) };
+      int c = 1, i = 0;
+      foreach (var node in root.IterateNodesBreadth()) {
+        for (int j = 0; j < node.SubtreeCount; ++j) {
+          var s = node.GetSubtree(j);
+          if (s.SubtreeCount > ushort.MaxValue) throw new ArgumentException("Number of subtrees is too big (>65.535)");
+          code[c + j] = new NativeInstruction { narg = (ushort)s.SubtreeCount, opcode = opCodeMapper(s) };
+        }
+
+        if (node is VariableTreeNode variable) {
+          code[i].weight = variable.Weight;
+          code[i].data = cachedData[variable.VariableName].AddrOfPinnedObject();
+        } else if (node is ConstantTreeNode constant) {
+          code[i].value = constant.Value;
+        }
+
+        code[i].childIndex = c;
+        c += node.SubtreeCount;
+        ++i;
+      }
+      return code;
+    }
+
+    private readonly object syncRoot = new object();
+
+    [ThreadStatic]
+    private static Dictionary<string, GCHandle> cachedData;
+
+    public IEnumerable<double> GetSymbolicExpressionTreeValues(ISymbolicExpressionTree tree, IDataset dataset, IEnumerable<int> rows) {
+      if (!rows.Any()) return Enumerable.Empty<double>();
+
+      lock (syncRoot) {
+        EvaluatedSolutions++; // increment the evaluated solutions counter
+      }
+
+      if (cachedData == null) {
+        InitCache(dataset);
+      }
+
+      var code = Compile(tree, OpCodes.MapSymbolToOpCode);
+
+      var rowsArray = rows.ToArray();
+      var result = new double[rowsArray.Length];
+
+      NativeWrapper.GetValuesVectorized(code, code.Length, rowsArray, rowsArray.Length, result);
+      return result;
+    }
+
+    private void InitCache(IDataset dataset) {
+      cachedData = new Dictionary<string, GCHandle>();
+      foreach (var v in dataset.DoubleVariables) {
+        var values = dataset.GetDoubleValues(v).ToArray();
+        var gch = GCHandle.Alloc(values, GCHandleType.Pinned);
+        cachedData[v] = gch;
+      }
+    }
+
+    public void InitializeState() {
+      if (cachedData != null) {
+        foreach (var gch in cachedData.Values) {
+          gch.Free();
+        }
+        cachedData = null;
+      }
+      EvaluatedSolutions = 0;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Plugin.cs.frame
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Plugin.cs.frame	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Plugin.cs.frame	(revision 16337)
@@ -0,0 +1,50 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+using HeuristicLab.PluginInfrastructure;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Plugin("HeuristicLab.Problems.DataAnalysis.Symbolic","Provides base classes for symbolic data analysis tasks.", "3.4.11.$WCREV$")]
+  [PluginFile("HeuristicLab.Problems.DataAnalysis.Symbolic-3.4.dll", PluginFileType.Assembly)]
+  [PluginDependency("HeuristicLab.ALGLIB", "3.7.0")]
+  [PluginDependency("HeuristicLab.AutoDiff", "1.0")]
+  [PluginDependency("HeuristicLab.Analysis", "3.3")]
+  [PluginDependency("HeuristicLab.Collections", "3.3")]
+  [PluginDependency("HeuristicLab.Common", "3.3")]
+  [PluginDependency("HeuristicLab.Common.Resources", "3.3")]
+  [PluginDependency("HeuristicLab.Core", "3.3")]
+  [PluginDependency("HeuristicLab.Data", "3.3")]
+  [PluginDependency("HeuristicLab.Encodings.SymbolicExpressionTreeEncoding", "3.4")]
+  [PluginDependency("HeuristicLab.NativeInterpreter", "0.1")]
+  [PluginDependency("HeuristicLab.Operators", "3.3")]
+  [PluginDependency("HeuristicLab.Optimization", "3.3")]
+  [PluginDependency("HeuristicLab.Optimization.Operators", "3.3")]
+  [PluginDependency("HeuristicLab.Parameters", "3.3")]
+  [PluginDependency("HeuristicLab.Persistence", "3.3")]
+  [PluginDependency("HeuristicLab.Problems.DataAnalysis", "3.4")]
+  [PluginDependency("HeuristicLab.Problems.Instances", "3.3")]
+  [PluginDependency("HeuristicLab.Random", "3.3")]
+  public class HeuristicLabProblemsDataAnalysisSymbolicPlugin : PluginBase {
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Properties/AssemblyInfo.cs.frame
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Properties/AssemblyInfo.cs.frame	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Properties/AssemblyInfo.cs.frame	(revision 16337)
@@ -0,0 +1,55 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Reflection;
+using System.Runtime.InteropServices;
+
+// General Information about an assembly is controlled through the following 
+// set of attributes. Change these attribute values to modify the information
+// associated with an assembly.
+[assembly: AssemblyTitle("HeuristicLab.Problems.DataAnalysis.Symbolic")]
+[assembly: AssemblyDescription("Provides base classes for symbolic data analysis tasks.")]
+[assembly: AssemblyConfiguration("")]
+[assembly: AssemblyCompany("")]
+[assembly: AssemblyProduct("HeuristicLab")]
+[assembly: AssemblyCopyright("(c) 2002-2018 HEAL")]
+[assembly: AssemblyTrademark("")]
+[assembly: AssemblyCulture("")]
+
+// Setting ComVisible to false makes the types in this assembly not visible 
+// to COM components.  If you need to access a type in this assembly from 
+// COM, set the ComVisible attribute to true on that type.
+[assembly: ComVisible(false)]
+
+// The following GUID is for the ID of the typelib if this project is exposed to COM
+[assembly: Guid("ABF1DB5E-5774-48AB-B65A-5CF405C0E2A8")]
+
+// Version information for an assembly consists of the following four values:
+//
+//      Major Version
+//      Minor Version 
+//      Build Number
+//      Revision
+//
+// You can specify all the values or you can default the Revision and Build Numbers 
+// by using the '*' as shown below:
+[assembly: AssemblyVersion("3.4.0.0")]
+[assembly: AssemblyFileVersion("3.4.11.$WCREV$")]
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisExpressionPruningOperator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisExpressionPruningOperator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisExpressionPruningOperator.cs	(revision 16337)
@@ -0,0 +1,214 @@
+﻿#region License Information
+
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#endregion
+
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Operators;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicExpressionTreePruningOperator", "An operator that replaces introns with constant values in a symbolic expression tree.")]
+  public abstract class SymbolicDataAnalysisExpressionPruningOperator : SingleSuccessorOperator, ISymbolicExpressionTreeOperator {
+    #region parameter names
+    private const string ProblemDataParameterName = "ProblemData";
+    private const string SymbolicDataAnalysisModelParameterName = "SymbolicDataAnalysisModel";
+    private const string ImpactValuesCalculatorParameterName = "ImpactValuesCalculator";
+    private const string PrunedSubtreesParameterName = "PrunedSubtrees";
+    private const string PrunedTreesParameterName = "PrunedTrees";
+    private const string PrunedNodesParameterName = "PrunedNodes";
+    private const string FitnessCalculationPartitionParameterName = "FitnessCalculationPartition";
+    private const string NodeImpactThresholdParameterName = "ImpactThreshold";
+    private const string PruneOnlyZeroImpactNodesParameterName = "PruneOnlyZeroImpactNodes";
+    private const string SymbolicExpressionTreeParameterName = "SymbolicExpressionTree"; // the tree to be pruned
+    private const string QualityParameterName = "Quality"; // the quality 
+    private const string EstimationLimitsParameterName = "EstimationLimits";
+    private const string InterpreterParameterName = "SymbolicExpressionTreeInterpreter";
+    private const string ApplyLinearScalingParameterName = "ApplyLinearScaling";
+    #endregion
+
+    #region parameter properties
+    public ILookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter {
+      get { return (ILookupParameter<ISymbolicExpressionTree>)Parameters[SymbolicExpressionTreeParameterName]; }
+    }
+    public ILookupParameter<DoubleValue> QualityParameter {
+      get { return (ILookupParameter<DoubleValue>)Parameters[QualityParameterName]; }
+    }
+    public ILookupParameter<IDataAnalysisProblemData> ProblemDataParameter {
+      get { return (ILookupParameter<IDataAnalysisProblemData>)Parameters[ProblemDataParameterName]; }
+    }
+    public IValueParameter<ISymbolicDataAnalysisSolutionImpactValuesCalculator> ImpactValuesCalculatorParameter {
+      get { return (IValueParameter<ISymbolicDataAnalysisSolutionImpactValuesCalculator>)Parameters[ImpactValuesCalculatorParameterName]; }
+    }
+    public ILookupParameter<IntRange> FitnessCalculationPartitionParameter {
+      get { return (ILookupParameter<IntRange>)Parameters[FitnessCalculationPartitionParameterName]; }
+    }
+    public ILookupParameter<IntValue> PrunedSubtreesParameter {
+      get { return (ILookupParameter<IntValue>)Parameters[PrunedSubtreesParameterName]; }
+    }
+    public ILookupParameter<IntValue> PrunedTreesParameter {
+      get { return (ILookupParameter<IntValue>)Parameters[PrunedTreesParameterName]; }
+    }
+    public ILookupParameter<IntValue> PrunedNodesParameter {
+      get { return (ILookupParameter<IntValue>)Parameters[PrunedNodesParameterName]; }
+    }
+    public IFixedValueParameter<DoubleValue> NodeImpactThresholdParameter {
+      get { return (IFixedValueParameter<DoubleValue>)Parameters[NodeImpactThresholdParameterName]; }
+    }
+    public IFixedValueParameter<BoolValue> PruneOnlyZeroImpactNodesParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[PruneOnlyZeroImpactNodesParameterName]; }
+    }
+    public ILookupParameter<DoubleLimit> EstimationLimitsParameter {
+      get { return (ILookupParameter<DoubleLimit>)Parameters[EstimationLimitsParameterName]; }
+    }
+    public ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> InterpreterParameter {
+      get { return (ILookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>)Parameters[InterpreterParameterName]; }
+    }
+    public ILookupParameter<BoolValue> ApplyLinearScalingParameter {
+      get { return (ILookupParameter<BoolValue>)Parameters[ApplyLinearScalingParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    public ISymbolicDataAnalysisSolutionImpactValuesCalculator ImpactValuesCalculator {
+      get { return ImpactValuesCalculatorParameter.Value; }
+      set { ImpactValuesCalculatorParameter.Value = value; }
+    }
+    public bool PruneOnlyZeroImpactNodes {
+      get { return PruneOnlyZeroImpactNodesParameter.Value.Value; }
+      set { PruneOnlyZeroImpactNodesParameter.Value.Value = value; }
+    }
+    public double NodeImpactThreshold {
+      get { return NodeImpactThresholdParameter.Value.Value; }
+      set { NodeImpactThresholdParameter.Value.Value = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionPruningOperator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisExpressionPruningOperator(SymbolicDataAnalysisExpressionPruningOperator original, Cloner cloner)
+      : base(original, cloner) { }
+
+    protected SymbolicDataAnalysisExpressionPruningOperator(ISymbolicDataAnalysisSolutionImpactValuesCalculator impactValuesCalculator) {
+      #region add parameters
+      Parameters.Add(new LookupParameter<IDataAnalysisProblemData>(ProblemDataParameterName));
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisModel>(SymbolicDataAnalysisModelParameterName));
+      Parameters.Add(new LookupParameter<IntRange>(FitnessCalculationPartitionParameterName));
+      Parameters.Add(new LookupParameter<IntValue>(PrunedNodesParameterName, "A counter of how many nodes were pruned."));
+      Parameters.Add(new LookupParameter<IntValue>(PrunedSubtreesParameterName, "A counter of how many subtrees were replaced."));
+      Parameters.Add(new LookupParameter<IntValue>(PrunedTreesParameterName, "A counter of how many trees were pruned."));
+      Parameters.Add(new FixedValueParameter<BoolValue>(PruneOnlyZeroImpactNodesParameterName, "Specify whether or not only zero impact nodes should be pruned."));
+      Parameters.Add(new FixedValueParameter<DoubleValue>(NodeImpactThresholdParameterName, "Specifies an impact value threshold below which nodes should be pruned."));
+      Parameters.Add(new LookupParameter<DoubleLimit>(EstimationLimitsParameterName));
+      Parameters.Add(new LookupParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>(InterpreterParameterName));
+      Parameters.Add(new LookupParameter<ISymbolicExpressionTree>(SymbolicExpressionTreeParameterName));
+      Parameters.Add(new LookupParameter<DoubleValue>(QualityParameterName));
+      Parameters.Add(new LookupParameter<BoolValue>(ApplyLinearScalingParameterName));
+      Parameters.Add(new ValueParameter<ISymbolicDataAnalysisSolutionImpactValuesCalculator>(ImpactValuesCalculatorParameterName, impactValuesCalculator));
+      #endregion
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      // BackwardsCompatibility3.3
+      #region Backwards compatible code, remove with 3.4
+      if (!Parameters.ContainsKey(PrunedNodesParameterName)) {
+        Parameters.Add(new LookupParameter<IntValue>(PrunedNodesParameterName, "A counter of how many nodes were pruned."));
+      }
+      if (!Parameters.ContainsKey(ApplyLinearScalingParameterName)) {
+        Parameters.Add(new LookupParameter<BoolValue>(ApplyLinearScalingParameterName));
+      }
+      if (!Parameters.ContainsKey(ImpactValuesCalculatorParameterName)) {
+        // value must be set by derived operators (regression/classification)
+        Parameters.Add(new ValueParameter<ISymbolicDataAnalysisSolutionImpactValuesCalculator>(ImpactValuesCalculatorParameterName));
+      }
+      #endregion
+    }
+
+    protected abstract ISymbolicDataAnalysisModel CreateModel(ISymbolicExpressionTree tree, ISymbolicDataAnalysisExpressionTreeInterpreter interpreter, IDataAnalysisProblemData problemData, DoubleLimit estimationLimits);
+
+    protected abstract double Evaluate(IDataAnalysisModel model);
+
+    public override IOperation Apply() {
+      var tree = SymbolicExpressionTreeParameter.ActualValue;
+      var problemData = ProblemDataParameter.ActualValue;
+      var fitnessCalculationPartition = FitnessCalculationPartitionParameter.ActualValue;
+      var estimationLimits = EstimationLimitsParameter.ActualValue;
+      var interpreter = InterpreterParameter.ActualValue;
+
+      var model = CreateModel(tree, interpreter, problemData, estimationLimits);
+      var nodes = tree.Root.GetSubtree(0).GetSubtree(0).IterateNodesPrefix().ToList();
+      var rows = Enumerable.Range(fitnessCalculationPartition.Start, fitnessCalculationPartition.Size).ToList();
+      var prunedSubtrees = 0;
+      var prunedTrees = 0;
+      var prunedNodes = 0;
+
+      double qualityForImpactsCalculation = double.NaN;
+
+      for (int i = 0; i < nodes.Count; ++i) {
+        var node = nodes[i];
+        if (node is ConstantTreeNode) continue;
+
+        double impactValue, replacementValue;
+        double newQualityForImpacts;
+        ImpactValuesCalculator.CalculateImpactAndReplacementValues(model, node, problemData, rows, out impactValue, out replacementValue, out newQualityForImpacts, qualityForImpactsCalculation);
+
+        if (PruneOnlyZeroImpactNodes && !impactValue.IsAlmost(0.0)) continue;
+        if (!PruneOnlyZeroImpactNodes && impactValue > NodeImpactThreshold) continue;
+
+        var constantNode = (ConstantTreeNode)node.Grammar.GetSymbol("Constant").CreateTreeNode();
+        constantNode.Value = replacementValue;
+
+        var length = node.GetLength();
+        ReplaceWithConstant(node, constantNode);
+        i += length - 1; // skip subtrees under the node that was folded
+
+        prunedSubtrees++;
+        prunedNodes += length;
+
+        qualityForImpactsCalculation = newQualityForImpacts;
+      }
+
+      if (prunedSubtrees > 0) prunedTrees = 1;
+      PrunedSubtreesParameter.ActualValue = new IntValue(prunedSubtrees);
+      PrunedTreesParameter.ActualValue = new IntValue(prunedTrees);
+      PrunedNodesParameter.ActualValue = new IntValue(prunedNodes);
+
+      if (prunedSubtrees > 0) // if nothing was pruned then there's no need to re-evaluate the tree
+        QualityParameter.ActualValue.Value = Evaluate(model);
+
+      return base.Apply();
+    }
+
+    protected static void ReplaceWithConstant(ISymbolicExpressionTreeNode original, ISymbolicExpressionTreeNode replacement) {
+      var parent = original.Parent;
+      var i = parent.IndexOfSubtree(original);
+      parent.RemoveSubtree(i);
+      parent.InsertSubtree(i, replacement);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisExpressionTreeSimplificationOperator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisExpressionTreeSimplificationOperator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisExpressionTreeSimplificationOperator.cs	(revision 16337)
@@ -0,0 +1,60 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Operators;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("SymbolicExpressionTreeSimplificationOperator", "Simplifies symbolic expression trees encoding a mathematical formula.")]
+  [StorableClass]
+  public class SymbolicDataAnalysisExpressionTreeSimplificationOperator : SingleSuccessorOperator, ISymbolicExpressionTreeOperator {
+    private const string SymbolicExpressionTreeParameterName = "SymbolicExpressionTree";
+
+    public ILookupParameter<ISymbolicExpressionTree> SymbolicExpressionTreeParameter {
+      get { return (ILookupParameter<ISymbolicExpressionTree>)Parameters[SymbolicExpressionTreeParameterName]; }
+    }
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisExpressionTreeSimplificationOperator(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisExpressionTreeSimplificationOperator(SymbolicDataAnalysisExpressionTreeSimplificationOperator original, Cloner cloner)
+      : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicDataAnalysisExpressionTreeSimplificationOperator(this, cloner);
+    }
+
+    public SymbolicDataAnalysisExpressionTreeSimplificationOperator() {
+      Parameters.Add(new LookupParameter<ISymbolicExpressionTree>(SymbolicExpressionTreeParameterName, "The symbolic expression tree to simplify."));
+    }
+
+    public override IOperation Apply() {
+      var tree = SymbolicExpressionTreeParameter.ActualValue;
+      var simplifiedTree = TreeSimplifier.Simplify(tree);
+      simplifiedTree = TreeSimplifier.Simplify(simplifiedTree);
+      SymbolicExpressionTreeParameter.ActualValue = simplifiedTree;
+
+      return base.Apply();
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisModel.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisModel.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisModel.cs	(revision 16337)
@@ -0,0 +1,177 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Drawing;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  /// <summary>
+  /// Abstract base class for symbolic data analysis models
+  /// </summary>
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisModel : DataAnalysisModel, ISymbolicDataAnalysisModel {
+    public static new Image StaticItemImage {
+      get { return HeuristicLab.Common.Resources.VSImageLibrary.Function; }
+    }
+
+    #region properties
+    [Storable]
+    private double lowerEstimationLimit;
+    public double LowerEstimationLimit { get { return lowerEstimationLimit; } }
+    [Storable]
+    private double upperEstimationLimit;
+    public double UpperEstimationLimit { get { return upperEstimationLimit; } }
+
+    [Storable]
+    private ISymbolicExpressionTree symbolicExpressionTree;
+    public ISymbolicExpressionTree SymbolicExpressionTree {
+      get { return symbolicExpressionTree; }
+    }
+
+    [Storable]
+    private ISymbolicDataAnalysisExpressionTreeInterpreter interpreter;
+    public ISymbolicDataAnalysisExpressionTreeInterpreter Interpreter {
+      get { return interpreter; }
+    }
+
+    public override IEnumerable<string> VariablesUsedForPrediction {
+      get {
+        var variables =
+          SymbolicExpressionTree.IterateNodesPrefix()
+            .OfType<IVariableTreeNode>()
+            .Select(x => x.VariableName)
+            .Distinct();
+
+        return variables.OrderBy(x => x);
+      }
+    }
+
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisModel(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisModel(SymbolicDataAnalysisModel original, Cloner cloner)
+      : base(original, cloner) {
+      this.symbolicExpressionTree = cloner.Clone(original.symbolicExpressionTree);
+      this.interpreter = cloner.Clone(original.interpreter);
+      this.lowerEstimationLimit = original.lowerEstimationLimit;
+      this.upperEstimationLimit = original.upperEstimationLimit;
+    }
+    protected SymbolicDataAnalysisModel(ISymbolicExpressionTree tree, ISymbolicDataAnalysisExpressionTreeInterpreter interpreter,
+       double lowerEstimationLimit, double upperEstimationLimit)
+      : base() {
+      this.name = ItemName;
+      this.description = ItemDescription;
+      this.symbolicExpressionTree = tree;
+      this.interpreter = interpreter;
+      this.lowerEstimationLimit = lowerEstimationLimit;
+      this.upperEstimationLimit = upperEstimationLimit;
+    }
+
+    #region Scaling
+    protected void Scale(IDataAnalysisProblemData problemData, string targetVariable) {
+      var dataset = problemData.Dataset;
+      var rows = problemData.TrainingIndices;
+      var estimatedValues = Interpreter.GetSymbolicExpressionTreeValues(SymbolicExpressionTree, dataset, rows);
+      var targetValues = dataset.GetDoubleValues(targetVariable, rows);
+
+      var linearScalingCalculator = new OnlineLinearScalingParameterCalculator();
+      var targetValuesEnumerator = targetValues.GetEnumerator();
+      var estimatedValuesEnumerator = estimatedValues.GetEnumerator();
+      while (targetValuesEnumerator.MoveNext() & estimatedValuesEnumerator.MoveNext()) {
+        double target = targetValuesEnumerator.Current;
+        double estimated = estimatedValuesEnumerator.Current;
+        if (!double.IsNaN(estimated) && !double.IsInfinity(estimated))
+          linearScalingCalculator.Add(estimated, target);
+      }
+      if (linearScalingCalculator.ErrorState == OnlineCalculatorError.None && (targetValuesEnumerator.MoveNext() || estimatedValuesEnumerator.MoveNext()))
+        throw new ArgumentException("Number of elements in target and estimated values enumeration do not match.");
+
+      double alpha = linearScalingCalculator.Alpha;
+      double beta = linearScalingCalculator.Beta;
+      if (linearScalingCalculator.ErrorState != OnlineCalculatorError.None) return;
+
+      ConstantTreeNode alphaTreeNode = null;
+      ConstantTreeNode betaTreeNode = null;
+      // check if model has a structure that can be re-used for scaling
+      var startNode = SymbolicExpressionTree.Root.GetSubtree(0);
+      var addNode = startNode.GetSubtree(0);
+      if (addNode.Symbol is Addition && addNode.SubtreeCount == 2) {
+        alphaTreeNode = (ConstantTreeNode)addNode.Subtrees.LastOrDefault(n => n is ConstantTreeNode);
+        var mulNode = addNode.Subtrees.FirstOrDefault(n => n.Symbol is Multiplication);
+        if (mulNode != null) {
+          betaTreeNode = (ConstantTreeNode)mulNode.Subtrees.LastOrDefault(n => n is ConstantTreeNode);
+        }
+      }
+      // if tree structure matches the structure necessary for linear scaling then reuse the existing tree nodes
+      if (alphaTreeNode != null && betaTreeNode != null) {
+        betaTreeNode.Value *= beta;
+        alphaTreeNode.Value *= beta;
+        alphaTreeNode.Value += alpha;
+      } else {
+        var mainBranch = startNode.GetSubtree(0);
+        startNode.RemoveSubtree(0);
+        var scaledMainBranch = MakeSum(MakeProduct(mainBranch, beta), alpha);
+        startNode.AddSubtree(scaledMainBranch);
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeSum(ISymbolicExpressionTreeNode treeNode, double alpha) {
+      if (alpha.IsAlmost(0.0)) {
+        return treeNode;
+      } else {
+        var addition = new Addition();
+        var node = addition.CreateTreeNode();
+        var alphaConst = MakeConstant(alpha);
+        node.AddSubtree(treeNode);
+        node.AddSubtree(alphaConst);
+        return node;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeProduct(ISymbolicExpressionTreeNode treeNode, double beta) {
+      if (beta.IsAlmost(1.0)) {
+        return treeNode;
+      } else {
+        var multipliciation = new Multiplication();
+        var node = multipliciation.CreateTreeNode();
+        var betaConst = MakeConstant(beta);
+        node.AddSubtree(treeNode);
+        node.AddSubtree(betaConst);
+        return node;
+      }
+    }
+
+    private static ISymbolicExpressionTreeNode MakeConstant(double c) {
+      var node = (ConstantTreeNode)(new Constant()).CreateTreeNode();
+      node.Value = c;
+      return node;
+    }
+    #endregion
+
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisModelComplexityCalculator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisModelComplexityCalculator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisModelComplexityCalculator.cs	(revision 16337)
@@ -0,0 +1,99 @@
+﻿#region License Information
+
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#endregion
+
+using System;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class SymbolicDataAnalysisModelComplexityCalculator {
+    public static double CalculateComplexity(ISymbolicExpressionTree tree) {
+      return CalculateComplexity(tree.Root);
+    }
+    public static double CalculateComplexity(ISymbolicExpressionTreeNode treeNode) {
+      var node = treeNode;
+      if (node.Symbol is ProgramRootSymbol) node = node.GetSubtree(0);
+      if (node.Symbol is StartSymbol) node = node.GetSubtree(0);
+
+      switch (OpCodes.MapSymbolToOpCode(node)) {
+        case OpCodes.Constant: {
+            return 1;
+          }
+        case OpCodes.Variable:
+        case OpCodes.BinaryFactorVariable:
+        case OpCodes.FactorVariable: {
+            return 2;
+          }
+        case OpCodes.Add:
+        case OpCodes.Sub: {
+            double complexity = 0;
+            for (int i = 0; i < node.SubtreeCount; i++) {
+              complexity += CalculateComplexity(node.GetSubtree(i));
+            }
+            return complexity;
+          }
+        case OpCodes.Mul:
+        case OpCodes.Div: {
+            double complexity = 1;
+            for (int i = 0; i < node.SubtreeCount; i++) {
+              var nodeComplexity = CalculateComplexity(node.GetSubtree(i));
+              complexity *= nodeComplexity + 1;
+            }
+            return complexity;
+          }
+        case OpCodes.Sin:
+        case OpCodes.Cos:
+        case OpCodes.Tan:
+        case OpCodes.Exp:
+        case OpCodes.Log: {
+            double complexity = CalculateComplexity(node.GetSubtree(0));
+            return Math.Pow(2.0, complexity);
+          }
+        case OpCodes.Square: {
+            double complexity = CalculateComplexity(node.GetSubtree(0));
+            return complexity * complexity;
+          }
+        case OpCodes.SquareRoot: {
+            double complexity = CalculateComplexity(node.GetSubtree(0));
+            return complexity * complexity * complexity;
+          }
+        case OpCodes.Power:
+        case OpCodes.Root: {
+            double complexity = CalculateComplexity(node.GetSubtree(0));
+            var exponent = node.GetSubtree(1) as ConstantTreeNode;
+            if (exponent != null) {
+              double expVal = exponent.Value;
+              if (expVal < 0) expVal = Math.Abs(expVal);
+              if (expVal < 1) expVal = 1 / expVal;
+              return Math.Pow(complexity, Math.Round(expVal));
+            }
+
+            double expComplexity = CalculateComplexity(node.GetSubtree(1));
+            return Math.Pow(complexity, 2 * expComplexity);
+          }
+
+        default:
+          throw new NotSupportedException();
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisMultiObjectiveProblem.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisMultiObjectiveProblem.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisMultiObjectiveProblem.cs	(revision 16337)
@@ -0,0 +1,101 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisMultiObjectiveProblem<T, U, V> : SymbolicDataAnalysisProblem<T, U, V>, ISymbolicDataAnalysisMultiObjectiveProblem
+    where T : class,IDataAnalysisProblemData
+    where U : class, ISymbolicDataAnalysisMultiObjectiveEvaluator<T>
+    where V : class, ISymbolicDataAnalysisSolutionCreator {
+    private const string MaximizationParameterName = "Maximization";
+    private const string BestKnownQualityParameterName = "BestKnownQuality";
+
+    #region parameter properties
+    public IValueParameter<BoolArray> MaximizationParameter {
+      get { return (IValueParameter<BoolArray>)Parameters[MaximizationParameterName]; }
+    }
+    IParameter IMultiObjectiveHeuristicOptimizationProblem.MaximizationParameter {
+      get { return MaximizationParameter; }
+    }
+    #endregion
+
+    #region properties
+    public BoolArray Maximization {
+      get { return MaximizationParameter.Value; }
+      set { MaximizationParameter.Value = value; }
+    }
+    IMultiObjectiveEvaluator IMultiObjectiveHeuristicOptimizationProblem.Evaluator {
+      get { return Evaluator; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisMultiObjectiveProblem(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisMultiObjectiveProblem(SymbolicDataAnalysisMultiObjectiveProblem<T, U, V> original, Cloner cloner)
+      : base(original, cloner) {
+      RegisterEventHandler();
+    }
+
+    public SymbolicDataAnalysisMultiObjectiveProblem(T problemData, U evaluator, V solutionCreator)
+      : base(problemData, evaluator, solutionCreator) {
+      Parameters.Add(new ValueParameter<BoolArray>(MaximizationParameterName, "Set to false if the problem should be minimized."));
+
+      ParameterizeOperators();
+      RegisterEventHandler();
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      RegisterEventHandler();
+    }
+
+    private void RegisterEventHandler() {
+      Evaluator.QualitiesParameter.ActualNameChanged += new System.EventHandler(QualitiesParameter_ActualNameChanged);
+    }
+
+    protected override void OnEvaluatorChanged() {
+      base.OnEvaluatorChanged();
+      Evaluator.QualitiesParameter.ActualNameChanged += new System.EventHandler(QualitiesParameter_ActualNameChanged);
+      Maximization = new BoolArray(Evaluator.Maximization.ToArray());
+      ParameterizeOperators();
+    }
+
+    private void QualitiesParameter_ActualNameChanged(object sender, System.EventArgs e) {
+      ParameterizeOperators();
+    }
+
+    protected override void ParameterizeOperators() {
+      base.ParameterizeOperators();
+      foreach (var op in Operators.OfType<ISymbolicDataAnalysisMultiObjectiveAnalyzer>()) {
+        op.QualitiesParameter.ActualName = Evaluator.QualitiesParameter.ActualName;
+        op.MaximizationParameter.ActualName = MaximizationParameterName;
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisProblem.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisProblem.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisProblem.cs	(revision 16337)
@@ -0,0 +1,394 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Drawing;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Common.Resources;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.PluginInfrastructure;
+using HeuristicLab.Problems.Instances;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisProblem<T, U, V> : HeuristicOptimizationProblem<U, V>, IDataAnalysisProblem<T>, ISymbolicDataAnalysisProblem, IStorableContent,
+    IProblemInstanceConsumer<T>, IProblemInstanceExporter<T>
+    where T : class, IDataAnalysisProblemData
+    where U : class, ISymbolicDataAnalysisEvaluator<T>
+    where V : class, ISymbolicDataAnalysisSolutionCreator {
+
+    #region parameter names & descriptions
+    private const string ProblemDataParameterName = "ProblemData";
+    private const string SymbolicExpressionTreeGrammarParameterName = "SymbolicExpressionTreeGrammar";
+    private const string SymbolicExpressionTreeInterpreterParameterName = "SymbolicExpressionTreeInterpreter";
+    private const string MaximumSymbolicExpressionTreeDepthParameterName = "MaximumSymbolicExpressionTreeDepth";
+    private const string MaximumSymbolicExpressionTreeLengthParameterName = "MaximumSymbolicExpressionTreeLength";
+    private const string MaximumFunctionDefinitionsParameterName = "MaximumFunctionDefinitions";
+    private const string MaximumFunctionArgumentsParameterName = "MaximumFunctionArguments";
+    private const string RelativeNumberOfEvaluatedSamplesParameterName = "RelativeNumberOfEvaluatedSamples";
+    private const string FitnessCalculationPartitionParameterName = "FitnessCalculationPartition";
+    private const string ValidationPartitionParameterName = "ValidationPartition";
+    private const string ApplyLinearScalingParameterName = "ApplyLinearScaling";
+
+    private const string ProblemDataParameterDescription = "";
+    private const string SymbolicExpressionTreeGrammarParameterDescription = "The grammar that should be used for symbolic expression tree.";
+    private const string SymoblicExpressionTreeInterpreterParameterDescription = "The interpreter that should be used to evaluate the symbolic expression tree.";
+    private const string MaximumSymbolicExpressionTreeDepthParameterDescription = "Maximal depth of the symbolic expression. The minimum depth needed for the algorithm is 3 because two levels are reserved for the ProgramRoot and the Start symbol.";
+    private const string MaximumSymbolicExpressionTreeLengthParameterDescription = "Maximal length of the symbolic expression.";
+    private const string MaximumFunctionDefinitionsParameterDescription = "Maximal number of automatically defined functions";
+    private const string MaximumFunctionArgumentsParameterDescription = "Maximal number of arguments of automatically defined functions.";
+    private const string RelativeNumberOfEvaluatedSamplesParameterDescription = "The relative number of samples of the dataset partition, which should be randomly chosen for evaluation.";
+    private const string FitnessCalculationPartitionParameterDescription = "The partition of the problem data training partition, that should be used to calculate the fitness of an individual.";
+    private const string ValidationPartitionParameterDescription = "The partition of the problem data training partition, that should be used to select the best model from (optional).";
+    private const string ApplyLinearScalingParameterDescription = "Flag that indicates if the individual should be linearly scaled before evaluating.";
+    #endregion
+
+    #region parameter properties
+    IParameter IDataAnalysisProblem.ProblemDataParameter {
+      get { return ProblemDataParameter; }
+    }
+    public IValueParameter<T> ProblemDataParameter {
+      get { return (IValueParameter<T>)Parameters[ProblemDataParameterName]; }
+    }
+    public IValueParameter<ISymbolicDataAnalysisGrammar> SymbolicExpressionTreeGrammarParameter {
+      get { return (IValueParameter<ISymbolicDataAnalysisGrammar>)Parameters[SymbolicExpressionTreeGrammarParameterName]; }
+    }
+    public IValueParameter<ISymbolicDataAnalysisExpressionTreeInterpreter> SymbolicExpressionTreeInterpreterParameter {
+      get { return (IValueParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>)Parameters[SymbolicExpressionTreeInterpreterParameterName]; }
+    }
+    public IFixedValueParameter<IntValue> MaximumSymbolicExpressionTreeDepthParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeDepthParameterName]; }
+    }
+    public IFixedValueParameter<IntValue> MaximumSymbolicExpressionTreeLengthParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeLengthParameterName]; }
+    }
+    public IFixedValueParameter<IntValue> MaximumFunctionDefinitionsParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[MaximumFunctionDefinitionsParameterName]; }
+    }
+    public IFixedValueParameter<IntValue> MaximumFunctionArgumentsParameter {
+      get { return (IFixedValueParameter<IntValue>)Parameters[MaximumFunctionArgumentsParameterName]; }
+    }
+    public IFixedValueParameter<PercentValue> RelativeNumberOfEvaluatedSamplesParameter {
+      get { return (IFixedValueParameter<PercentValue>)Parameters[RelativeNumberOfEvaluatedSamplesParameterName]; }
+    }
+    public IFixedValueParameter<IntRange> FitnessCalculationPartitionParameter {
+      get { return (IFixedValueParameter<IntRange>)Parameters[FitnessCalculationPartitionParameterName]; }
+    }
+    public IFixedValueParameter<IntRange> ValidationPartitionParameter {
+      get { return (IFixedValueParameter<IntRange>)Parameters[ValidationPartitionParameterName]; }
+    }
+    public IFixedValueParameter<BoolValue> ApplyLinearScalingParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[ApplyLinearScalingParameterName]; }
+    }
+    #endregion
+
+    #region properties
+    public string Filename { get; set; }
+    public static new Image StaticItemImage { get { return VSImageLibrary.Type; } }
+
+    IDataAnalysisProblemData IDataAnalysisProblem.ProblemData {
+      get { return ProblemData; }
+    }
+    public T ProblemData {
+      get { return ProblemDataParameter.Value; }
+      set { ProblemDataParameter.Value = value; }
+    }
+
+    public ISymbolicDataAnalysisGrammar SymbolicExpressionTreeGrammar {
+      get { return SymbolicExpressionTreeGrammarParameter.Value; }
+      set { SymbolicExpressionTreeGrammarParameter.Value = value; }
+    }
+    public ISymbolicDataAnalysisExpressionTreeInterpreter SymbolicExpressionTreeInterpreter {
+      get { return SymbolicExpressionTreeInterpreterParameter.Value; }
+      set { SymbolicExpressionTreeInterpreterParameter.Value = value; }
+    }
+
+    public IntValue MaximumSymbolicExpressionTreeDepth {
+      get { return MaximumSymbolicExpressionTreeDepthParameter.Value; }
+    }
+    public IntValue MaximumSymbolicExpressionTreeLength {
+      get { return MaximumSymbolicExpressionTreeLengthParameter.Value; }
+    }
+    public IntValue MaximumFunctionDefinitions {
+      get { return MaximumFunctionDefinitionsParameter.Value; }
+    }
+    public IntValue MaximumFunctionArguments {
+      get { return MaximumFunctionArgumentsParameter.Value; }
+    }
+    public PercentValue RelativeNumberOfEvaluatedSamples {
+      get { return RelativeNumberOfEvaluatedSamplesParameter.Value; }
+    }
+
+    public IntRange FitnessCalculationPartition {
+      get { return FitnessCalculationPartitionParameter.Value; }
+    }
+    public IntRange ValidationPartition {
+      get { return ValidationPartitionParameter.Value; }
+    }
+    public BoolValue ApplyLinearScaling {
+      get { return ApplyLinearScalingParameter.Value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisProblem(bool deserializing) : base(deserializing) { }
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (!Parameters.ContainsKey(ApplyLinearScalingParameterName)) {
+        Parameters.Add(new FixedValueParameter<BoolValue>(ApplyLinearScalingParameterName, ApplyLinearScalingParameterDescription, new BoolValue(false)));
+        ApplyLinearScalingParameter.Hidden = true;
+
+        //it is assumed that for all symbolic regression algorithms linear scaling was set to true
+        //there is no possibility to determine the previous value of the parameter as it was stored in the evaluator
+        if (GetType().Name.Contains("SymbolicRegression"))
+          ApplyLinearScaling.Value = true;
+      }
+
+      RegisterEventHandlers();
+    }
+    protected SymbolicDataAnalysisProblem(SymbolicDataAnalysisProblem<T, U, V> original, Cloner cloner)
+      : base(original, cloner) {
+      RegisterEventHandlers();
+    }
+
+    protected SymbolicDataAnalysisProblem(T problemData, U evaluator, V solutionCreator)
+      : base(evaluator, solutionCreator) {
+      Parameters.Add(new ValueParameter<T>(ProblemDataParameterName, ProblemDataParameterDescription, problemData));
+      Parameters.Add(new ValueParameter<ISymbolicDataAnalysisGrammar>(SymbolicExpressionTreeGrammarParameterName, SymbolicExpressionTreeGrammarParameterDescription));
+      Parameters.Add(new ValueParameter<ISymbolicDataAnalysisExpressionTreeInterpreter>(SymbolicExpressionTreeInterpreterParameterName, SymoblicExpressionTreeInterpreterParameterDescription));
+      Parameters.Add(new FixedValueParameter<IntValue>(MaximumSymbolicExpressionTreeDepthParameterName, MaximumSymbolicExpressionTreeDepthParameterDescription));
+      Parameters.Add(new FixedValueParameter<IntValue>(MaximumSymbolicExpressionTreeLengthParameterName, MaximumSymbolicExpressionTreeLengthParameterDescription));
+      Parameters.Add(new FixedValueParameter<IntValue>(MaximumFunctionDefinitionsParameterName, MaximumFunctionDefinitionsParameterDescription));
+      Parameters.Add(new FixedValueParameter<IntValue>(MaximumFunctionArgumentsParameterName, MaximumFunctionArgumentsParameterDescription));
+      Parameters.Add(new FixedValueParameter<IntRange>(FitnessCalculationPartitionParameterName, FitnessCalculationPartitionParameterDescription));
+      Parameters.Add(new FixedValueParameter<IntRange>(ValidationPartitionParameterName, ValidationPartitionParameterDescription));
+      Parameters.Add(new FixedValueParameter<PercentValue>(RelativeNumberOfEvaluatedSamplesParameterName, RelativeNumberOfEvaluatedSamplesParameterDescription, new PercentValue(1)));
+      Parameters.Add(new FixedValueParameter<BoolValue>(ApplyLinearScalingParameterName, ApplyLinearScalingParameterDescription, new BoolValue(false)));
+
+      SymbolicExpressionTreeInterpreterParameter.Hidden = true;
+      MaximumFunctionArgumentsParameter.Hidden = true;
+      MaximumFunctionDefinitionsParameter.Hidden = true;
+      ApplyLinearScalingParameter.Hidden = true;
+
+      SymbolicExpressionTreeGrammar = new TypeCoherentExpressionGrammar();
+      SymbolicExpressionTreeInterpreter = new SymbolicDataAnalysisExpressionTreeLinearInterpreter();
+
+      FitnessCalculationPartition.Start = ProblemData.TrainingPartition.Start;
+      FitnessCalculationPartition.End = ProblemData.TrainingPartition.End;
+
+      InitializeOperators();
+
+      UpdateGrammar();
+      RegisterEventHandlers();
+    }
+
+    protected virtual void UpdateGrammar() {
+      var problemData = ProblemData;
+      var ds = problemData.Dataset;
+      var grammar = SymbolicExpressionTreeGrammar;
+      grammar.MaximumFunctionArguments = MaximumFunctionArguments.Value;
+      grammar.MaximumFunctionDefinitions = MaximumFunctionDefinitions.Value;
+      foreach (var varSymbol in grammar.Symbols.OfType<HeuristicLab.Problems.DataAnalysis.Symbolic.VariableBase>()) {
+        if (!varSymbol.Fixed) {
+          varSymbol.AllVariableNames = problemData.InputVariables.Select(x => x.Value).Where(x => ds.VariableHasType<double>(x));
+          varSymbol.VariableNames = problemData.AllowedInputVariables.Where(x => ds.VariableHasType<double>(x));
+        }
+      }
+      foreach (var factorSymbol in grammar.Symbols.OfType<BinaryFactorVariable>()) {
+        if (!factorSymbol.Fixed) {
+          factorSymbol.AllVariableNames = problemData.InputVariables.Select(x => x.Value).Where(x => ds.VariableHasType<string>(x));
+          factorSymbol.VariableNames = problemData.AllowedInputVariables.Where(x => ds.VariableHasType<string>(x));
+          factorSymbol.VariableValues = factorSymbol.VariableNames
+            .ToDictionary(varName => varName, varName => ds.GetStringValues(varName).Distinct().ToList());
+        }
+      }
+      foreach (var factorSymbol in grammar.Symbols.OfType<FactorVariable>()) {
+        if (!factorSymbol.Fixed) {
+          factorSymbol.AllVariableNames = problemData.InputVariables.Select(x => x.Value).Where(x => ds.VariableHasType<string>(x));
+          factorSymbol.VariableNames = problemData.AllowedInputVariables.Where(x => ds.VariableHasType<string>(x));
+          factorSymbol.VariableValues = factorSymbol.VariableNames
+            .ToDictionary(varName => varName,
+            varName => ds.GetStringValues(varName).Distinct()
+            .Select((n, i) => Tuple.Create(n, i))
+            .ToDictionary(tup => tup.Item1, tup => tup.Item2));
+        }
+      }
+    }
+
+    private void InitializeOperators() {
+      var operators = new HashSet<IItem>(new TypeEqualityComparer<IItem>());
+      operators.Add(new SubtreeCrossover());
+      operators.Add(new MultiSymbolicExpressionTreeManipulator());
+
+      foreach (var op in ApplicationManager.Manager.GetInstances<ISymbolicExpressionTreeOperator>())
+        operators.Add(op);
+      foreach (var op in ApplicationManager.Manager.GetInstances<ISymbolicDataAnalysisExpressionCrossover<T>>())
+        operators.Add(op);
+
+      operators.Add(new SymbolicExpressionSymbolFrequencyAnalyzer());
+      operators.Add(new SymbolicDataAnalysisVariableFrequencyAnalyzer());
+      operators.Add(new MinAverageMaxSymbolicExpressionTreeLengthAnalyzer());
+      operators.Add(new SymbolicExpressionTreeLengthAnalyzer());
+      operators.Add(new SymbolicExpressionTreeBottomUpSimilarityCalculator());
+      operators.Add(new SymbolicDataAnalysisBottomUpDiversityAnalyzer(operators.OfType<SymbolicExpressionTreeBottomUpSimilarityCalculator>().First()));
+
+      Operators.AddRange(operators);
+      ParameterizeOperators();
+    }
+
+    #region events
+    private void RegisterEventHandlers() {
+      ProblemDataParameter.ValueChanged += new EventHandler(ProblemDataParameter_ValueChanged);
+      ProblemDataParameter.Value.Changed += (object sender, EventArgs e) => OnProblemDataChanged();
+
+      SymbolicExpressionTreeGrammarParameter.ValueChanged += new EventHandler(SymbolicExpressionTreeGrammarParameter_ValueChanged);
+
+      MaximumFunctionArguments.ValueChanged += new EventHandler(ArchitectureParameterValue_ValueChanged);
+      MaximumFunctionDefinitions.ValueChanged += new EventHandler(ArchitectureParameterValue_ValueChanged);
+      MaximumSymbolicExpressionTreeDepth.ValueChanged += new EventHandler(MaximumSymbolicExpressionTreeDepth_ValueChanged);
+    }
+
+    private void ProblemDataParameter_ValueChanged(object sender, EventArgs e) {
+      ValidationPartition.Start = 0;
+      ValidationPartition.End = 0;
+      ProblemDataParameter.Value.Changed += (object s, EventArgs args) => OnProblemDataChanged();
+      OnProblemDataChanged();
+    }
+
+    private void SymbolicExpressionTreeGrammarParameter_ValueChanged(object sender, EventArgs e) {
+      UpdateGrammar();
+    }
+
+    private void ArchitectureParameterValue_ValueChanged(object sender, EventArgs e) {
+      UpdateGrammar();
+    }
+
+    private void MaximumSymbolicExpressionTreeDepth_ValueChanged(object sender, EventArgs e) {
+      if (MaximumSymbolicExpressionTreeDepth != null && MaximumSymbolicExpressionTreeDepth.Value < 3)
+        MaximumSymbolicExpressionTreeDepth.Value = 3;
+    }
+
+    protected override void OnSolutionCreatorChanged() {
+      base.OnSolutionCreatorChanged();
+      SolutionCreator.SymbolicExpressionTreeParameter.ActualNameChanged += new EventHandler(SolutionCreator_SymbolicExpressionTreeParameter_ActualNameChanged);
+      ParameterizeOperators();
+    }
+
+    private void SolutionCreator_SymbolicExpressionTreeParameter_ActualNameChanged(object sender, EventArgs e) {
+      ParameterizeOperators();
+    }
+
+    protected override void OnEvaluatorChanged() {
+      base.OnEvaluatorChanged();
+      ParameterizeOperators();
+    }
+
+    public event EventHandler ProblemDataChanged;
+    protected virtual void OnProblemDataChanged() {
+      FitnessCalculationPartition.Start = ProblemData.TrainingPartition.Start;
+      FitnessCalculationPartition.End = ProblemData.TrainingPartition.End;
+
+      UpdateGrammar();
+      ParameterizeOperators();
+
+      var handler = ProblemDataChanged;
+      if (handler != null) handler(this, EventArgs.Empty);
+
+      OnReset();
+    }
+    #endregion
+
+    protected virtual void ParameterizeOperators() {
+      var operators = Parameters.OfType<IValueParameter>().Select(p => p.Value).OfType<IOperator>().Union(Operators).ToList();
+
+      foreach (var op in operators.OfType<ISymbolicExpressionTreeGrammarBasedOperator>()) {
+        op.SymbolicExpressionTreeGrammarParameter.ActualName = SymbolicExpressionTreeGrammarParameter.Name;
+      }
+      foreach (var op in operators.OfType<ISymbolicExpressionTreeSizeConstraintOperator>()) {
+        op.MaximumSymbolicExpressionTreeDepthParameter.ActualName = MaximumSymbolicExpressionTreeDepthParameter.Name;
+        op.MaximumSymbolicExpressionTreeLengthParameter.ActualName = MaximumSymbolicExpressionTreeLengthParameter.Name;
+      }
+      foreach (var op in operators.OfType<ISymbolicExpressionTreeArchitectureAlteringOperator>()) {
+        op.MaximumFunctionArgumentsParameter.ActualName = MaximumFunctionArgumentsParameter.Name;
+        op.MaximumFunctionDefinitionsParameter.ActualName = MaximumFunctionDefinitionsParameter.Name;
+      }
+      foreach (var op in operators.OfType<ISymbolicDataAnalysisEvaluator<T>>()) {
+        op.ProblemDataParameter.ActualName = ProblemDataParameterName;
+        op.SymbolicExpressionTreeParameter.ActualName = SolutionCreator.SymbolicExpressionTreeParameter.ActualName;
+        op.EvaluationPartitionParameter.ActualName = FitnessCalculationPartitionParameter.Name;
+        op.RelativeNumberOfEvaluatedSamplesParameter.ActualName = RelativeNumberOfEvaluatedSamplesParameter.Name;
+        op.ApplyLinearScalingParameter.ActualName = ApplyLinearScalingParameter.Name;
+      }
+      foreach (var op in operators.OfType<ISymbolicExpressionTreeCrossover>()) {
+        op.ParentsParameter.ActualName = SolutionCreator.SymbolicExpressionTreeParameter.ActualName;
+        op.SymbolicExpressionTreeParameter.ActualName = SolutionCreator.SymbolicExpressionTreeParameter.ActualName;
+      }
+      foreach (var op in operators.OfType<ISymbolicExpressionTreeManipulator>()) {
+        op.SymbolicExpressionTreeParameter.ActualName = SolutionCreator.SymbolicExpressionTreeParameter.ActualName;
+      }
+      foreach (var op in operators.OfType<ISymbolicExpressionTreeAnalyzer>()) {
+        op.SymbolicExpressionTreeParameter.ActualName = SolutionCreator.SymbolicExpressionTreeParameter.ActualName;
+      }
+      foreach (var op in operators.OfType<ISymbolicDataAnalysisSingleObjectiveAnalyzer>()) {
+        op.ApplyLinearScalingParameter.ActualName = ApplyLinearScalingParameter.Name;
+      }
+      foreach (var op in operators.OfType<ISymbolicDataAnalysisMultiObjectiveAnalyzer>()) {
+        op.ApplyLinearScalingParameter.ActualName = ApplyLinearScalingParameter.Name;
+      }
+      foreach (var op in operators.OfType<ISymbolicDataAnalysisAnalyzer>()) {
+        op.SymbolicExpressionTreeParameter.ActualName = SolutionCreator.SymbolicExpressionTreeParameter.ActualName;
+      }
+      foreach (var op in operators.OfType<ISymbolicDataAnalysisValidationAnalyzer<U, T>>()) {
+        op.RelativeNumberOfEvaluatedSamplesParameter.ActualName = RelativeNumberOfEvaluatedSamplesParameter.Name;
+        op.ValidationPartitionParameter.ActualName = ValidationPartitionParameter.Name;
+      }
+      foreach (var op in operators.OfType<ISymbolicDataAnalysisInterpreterOperator>()) {
+        op.SymbolicDataAnalysisTreeInterpreterParameter.ActualName = SymbolicExpressionTreeInterpreterParameter.Name;
+      }
+      foreach (var op in operators.OfType<ISymbolicDataAnalysisExpressionCrossover<T>>()) {
+        op.EvaluationPartitionParameter.ActualName = FitnessCalculationPartitionParameter.Name;
+        op.ProblemDataParameter.ActualName = ProblemDataParameter.Name;
+        op.EvaluationPartitionParameter.ActualName = FitnessCalculationPartitionParameter.Name;
+        op.RelativeNumberOfEvaluatedSamplesParameter.ActualName = RelativeNumberOfEvaluatedSamplesParameter.Name;
+        op.EvaluatorParameter.ActualName = EvaluatorParameter.Name;
+      }
+    }
+
+    #region Import & Export
+    public virtual void Load(T data) {
+      Name = data.Name;
+      Description = data.Description;
+      ProblemData = data;
+    }
+
+    public virtual T Export() {
+      return ProblemData;
+    }
+    #endregion
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisSingleObjectiveProblem.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisSingleObjectiveProblem.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisSingleObjectiveProblem.cs	(revision 16337)
@@ -0,0 +1,119 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Optimization;
+using HeuristicLab.Parameters;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class SymbolicDataAnalysisSingleObjectiveProblem<T, U, V> : SymbolicDataAnalysisProblem<T, U, V>, ISymbolicDataAnalysisSingleObjectiveProblem
+    where T : class,IDataAnalysisProblemData
+    where U : class, ISymbolicDataAnalysisSingleObjectiveEvaluator<T>
+    where V : class, ISymbolicDataAnalysisSolutionCreator {
+    private const string MaximizationParameterName = "Maximization";
+    private const string BestKnownQualityParameterName = "BestKnownQuality";
+
+    #region parameter properties
+    public IFixedValueParameter<BoolValue> MaximizationParameter {
+      get { return (IFixedValueParameter<BoolValue>)Parameters[MaximizationParameterName]; }
+    }
+    IParameter ISingleObjectiveHeuristicOptimizationProblem.MaximizationParameter {
+      get { return MaximizationParameter; }
+    }
+    public IFixedValueParameter<DoubleValue> BestKnownQualityParameter {
+      get { return (IFixedValueParameter<DoubleValue>)Parameters[BestKnownQualityParameterName]; }
+    }
+    IParameter ISingleObjectiveHeuristicOptimizationProblem.BestKnownQualityParameter {
+      get { return BestKnownQualityParameter; }
+    }
+    #endregion
+
+    #region properties
+    public BoolValue Maximization {
+      get { return MaximizationParameter.Value; }
+    }
+    public DoubleValue BestKnownQuality {
+      get { return BestKnownQualityParameter.Value; }
+    }
+    ISingleObjectiveEvaluator ISingleObjectiveHeuristicOptimizationProblem.Evaluator {
+      get { return Evaluator; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSingleObjectiveProblem(bool deserializing) : base(deserializing) { }
+    protected SymbolicDataAnalysisSingleObjectiveProblem(SymbolicDataAnalysisSingleObjectiveProblem<T, U, V> original, Cloner cloner)
+      : base(original, cloner) {
+      RegisterEventHandler();
+      MaximizationParameter.Hidden = true;
+    }
+
+    protected SymbolicDataAnalysisSingleObjectiveProblem(T problemData, U evaluator, V solutionCreator)
+      : base(problemData, evaluator, solutionCreator) {
+      Parameters.Add(new FixedValueParameter<BoolValue>(MaximizationParameterName, "Set to false if the problem should be minimized."));
+      Parameters.Add(new FixedValueParameter<DoubleValue>(BestKnownQualityParameterName, "The quality of the best known solution of this problem."));
+
+      MaximizationParameter.Hidden = true;
+      InitializeOperators();
+      RegisterEventHandler();
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      RegisterEventHandler();
+    }
+
+    private void InitializeOperators() {
+      Operators.Add(new SymbolicDataAnalysisAlleleFrequencyAnalyzer());
+      ParameterizeOperators();
+    }
+
+    private void RegisterEventHandler() {
+      Evaluator.QualityParameter.ActualNameChanged += new EventHandler(QualityParameter_ActualNameChanged);
+    }
+
+    protected override void OnEvaluatorChanged() {
+      base.OnEvaluatorChanged();
+      Evaluator.QualityParameter.ActualNameChanged += new EventHandler(QualityParameter_ActualNameChanged);
+      Maximization.Value = base.Evaluator.Maximization;
+      ParameterizeOperators();
+    }
+
+    private void QualityParameter_ActualNameChanged(object sender, EventArgs e) {
+      ParameterizeOperators();
+    }
+
+    protected override void ParameterizeOperators() {
+      base.ParameterizeOperators();
+
+      foreach (var op in Operators.OfType<ISymbolicDataAnalysisSingleObjectiveAnalyzer>()) {
+        op.QualityParameter.ActualName = Evaluator.QualityParameter.ActualName;
+        op.MaximizationParameter.ActualName = MaximizationParameterName;
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisSolutionImpactValuesCalculator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisSolutionImpactValuesCalculator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/SymbolicDataAnalysisSolutionImpactValuesCalculator.cs	(revision 16337)
@@ -0,0 +1,110 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicDataAnalysisSolutionImpactValuesCalculator", "Calculates the impact values and replacements values for symbolic expression tree nodes.")]
+  public abstract class SymbolicDataAnalysisSolutionImpactValuesCalculator : Item, ISymbolicDataAnalysisSolutionImpactValuesCalculator {
+    protected SymbolicDataAnalysisSolutionImpactValuesCalculator() { }
+    protected SymbolicDataAnalysisSolutionImpactValuesCalculator(SymbolicDataAnalysisSolutionImpactValuesCalculator original, Cloner cloner)
+      : base(original, cloner) { }
+    [StorableConstructor]
+    protected SymbolicDataAnalysisSolutionImpactValuesCalculator(bool deserializing) : base(deserializing) { }
+
+    public virtual void CalculateImpactAndReplacementValues(ISymbolicDataAnalysisModel model, ISymbolicExpressionTreeNode node, IDataAnalysisProblemData problemData, IEnumerable<int> rows,
+        out double impactValue, out double replacementValue, out double newQualityForImpactsCalculation,
+        double qualityForImpactsCalculation = double.NaN) {
+
+      var cloner = new Cloner();
+      var tempModel = cloner.Clone(model);
+
+      if (double.IsNaN(qualityForImpactsCalculation)) {
+        qualityForImpactsCalculation = CalculateQualityForImpacts(tempModel, problemData, rows);
+      }
+
+      var tempModelNode = (ISymbolicExpressionTreeNode)cloner.GetClone(node);
+      var tempModelParentNode = tempModelNode.Parent;
+      int i = tempModelParentNode.IndexOfSubtree(tempModelNode);
+
+      double bestReplacementValue = 0.0;
+      double bestImpactValue = double.PositiveInfinity;
+      newQualityForImpactsCalculation = qualityForImpactsCalculation; // initialize
+      // try the potentially reasonable replacement values and use the best one
+      foreach (var repValue in CalculateReplacementValues(node, model.SymbolicExpressionTree, model.Interpreter, problemData.Dataset, rows)) {
+        tempModelParentNode.RemoveSubtree(i);
+
+        var constantNode = new ConstantTreeNode(new Constant()) { Value = repValue };
+        tempModelParentNode.InsertSubtree(i, constantNode);
+
+        newQualityForImpactsCalculation = CalculateQualityForImpacts(tempModel, problemData, rows);
+
+        impactValue = qualityForImpactsCalculation - newQualityForImpactsCalculation;
+        if (impactValue < bestImpactValue) {
+          bestImpactValue = impactValue;
+          bestReplacementValue = repValue;
+        }
+      }
+
+      replacementValue = bestReplacementValue;
+      impactValue = bestImpactValue;
+    }
+
+    protected abstract double CalculateQualityForImpacts(ISymbolicDataAnalysisModel model, IDataAnalysisProblemData problemData, IEnumerable<int> rows);
+
+    protected IEnumerable<double> CalculateReplacementValues(ISymbolicExpressionTreeNode node, ISymbolicExpressionTree sourceTree, ISymbolicDataAnalysisExpressionTreeInterpreter interpreter,
+      IDataset dataset, IEnumerable<int> rows) {
+      //optimization: constant nodes return always the same value
+      ConstantTreeNode constantNode = node as ConstantTreeNode;
+      BinaryFactorVariableTreeNode binaryFactorNode = node as BinaryFactorVariableTreeNode;
+      FactorVariableTreeNode factorNode = node as FactorVariableTreeNode;
+      if (constantNode != null) {
+        yield return constantNode.Value;
+      } else if (binaryFactorNode != null) {
+        // valid replacements are either all off or all on
+        yield return 0;
+        yield return 1;
+      } else if (factorNode != null) {
+        foreach (var w in factorNode.Weights) yield return w;
+        yield return 0.0;
+      } else {
+        var rootSymbol = new ProgramRootSymbol().CreateTreeNode();
+        var startSymbol = new StartSymbol().CreateTreeNode();
+        rootSymbol.AddSubtree(startSymbol);
+        startSymbol.AddSubtree((ISymbolicExpressionTreeNode)node.Clone());
+
+        var tempTree = new SymbolicExpressionTree(rootSymbol);
+        // clone ADFs of source tree
+        for (int i = 1; i < sourceTree.Root.SubtreeCount; i++) {
+          tempTree.Root.AddSubtree((ISymbolicExpressionTreeNode)sourceTree.Root.GetSubtree(i).Clone());
+        }
+        yield return interpreter.GetSymbolicExpressionTreeValues(tempTree, dataset, rows).Median();
+        yield return interpreter.GetSymbolicExpressionTreeValues(tempTree, dataset, rows).Average(); // TODO perf
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Addition.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Addition.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Addition.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Addition", "Symbol that represents the + operator.")]
+  public sealed class Addition : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = byte.MaxValue;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Addition(bool deserializing) : base(deserializing) { }
+    private Addition(Addition original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Addition(this, cloner);
+    }
+    public Addition() : base("Addition", "Symbol that represents the + operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AiryA.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AiryA.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AiryA.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("AiryA", "Symbol that represents the Airy A function.")]
+  public sealed class AiryA : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private AiryA(bool deserializing) : base(deserializing) { }
+    private AiryA(AiryA original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new AiryA(this, cloner);
+    }
+    public AiryA() : base("AiryA", "Symbol that represents the Airy A function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AiryB.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AiryB.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AiryB.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("AiryB", "Symbol that represents the Airy B function.")]
+  public sealed class AiryB : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private AiryB(bool deserializing) : base(deserializing) { }
+    private AiryB(AiryB original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new AiryB(this, cloner);
+    }
+    public AiryB() : base("AiryB", "Symbol that represents the Airy B function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/And.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/And.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/And.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("And", "Symbol that represents the boolean AND operator.")]
+  public sealed class And : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = byte.MaxValue;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private And(bool deserializing) : base(deserializing) { }
+    private And(And original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new And(this, cloner);
+    }
+    public And() : base("And", "Symbol that represents the boolean AND operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AutoregressiveVariable.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AutoregressiveVariable.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/AutoregressiveVariable.cs	(revision 16337)
@@ -0,0 +1,39 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("AutoregressiveTargetVariable", "Represents a variable value with a time offset.")]
+  public sealed class AutoregressiveTargetVariable : LaggedVariable {
+    [StorableConstructor]
+    private AutoregressiveTargetVariable(bool deserializing) : base(deserializing) { }
+    private AutoregressiveTargetVariable(AutoregressiveTargetVariable original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public AutoregressiveTargetVariable() : base("Autoregressive Target Variable", "Represents the target variable with a time offset.") { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new AutoregressiveTargetVariable(this, cloner);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Average.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Average.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Average.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Average", "Symbol that represents the average (arithmetic mean) function.")]
+  public sealed class Average : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = byte.MaxValue;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Average(bool deserializing) : base(deserializing) { }
+    private Average(Average original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Average(this, cloner);
+    }
+    public Average() : base("Average", "Symbol that represents the average (arithmetic mean) function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Bessel.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Bessel.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Bessel.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Bessel", "Symbol that represents the Bessel function.")]
+  public sealed class Bessel : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Bessel(bool deserializing) : base(deserializing) { }
+    private Bessel(Bessel original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Bessel(this, cloner);
+    }
+    public Bessel() : base("Bessel", "Symbol that represents the Bessel function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/BinaryFactorVariable.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/BinaryFactorVariable.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/BinaryFactorVariable.cs	(revision 16337)
@@ -0,0 +1,76 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("BinaryFactorVariable", "Represents a categorical variable (comparable to factors as in R) and it's value.")]
+  public sealed class BinaryFactorVariable : VariableBase {
+
+    private readonly Dictionary<string, List<string>> variableValues;
+
+    [Storable]
+    public IEnumerable<KeyValuePair<string, List<string>>> VariableValues {
+      get { return variableValues; }
+      set {
+        if (value == null) throw new ArgumentNullException();
+        variableValues.Clear();
+        foreach (var kvp in value) {
+          variableValues.Add(kvp.Key, new List<string>(kvp.Value));
+        }
+      }
+    }
+
+    [StorableConstructor]
+    private BinaryFactorVariable(bool deserializing)
+      : base(deserializing) {
+      variableValues = new Dictionary<string, List<string>>();
+    }
+    private BinaryFactorVariable(BinaryFactorVariable original, Cloner cloner)
+      : base(original, cloner) {
+      variableValues =
+        original.variableValues.ToDictionary(kvp => kvp.Key, kvp => new List<string>(kvp.Value));
+    }
+    public BinaryFactorVariable() : this("BinaryFactorVariable", "Represents a categorical variable (comparable to factors as in R) and it's value.") { }
+    public BinaryFactorVariable(string name, string description)
+      : base(name, description) {
+      variableValues = new Dictionary<string, List<string>>();
+    }
+
+    public override ISymbolicExpressionTreeNode CreateTreeNode() {
+      return new BinaryFactorVariableTreeNode(this);
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new BinaryFactorVariable(this, cloner);
+    }
+
+    public IEnumerable<string> GetVariableValues(string variableName) {
+      return variableValues[variableName];
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/BinaryFactorVariableTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/BinaryFactorVariableTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/BinaryFactorVariableTreeNode.cs	(revision 16337)
@@ -0,0 +1,84 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public sealed class BinaryFactorVariableTreeNode : VariableTreeNodeBase {
+    public new BinaryFactorVariable Symbol {
+      get { return (BinaryFactorVariable)base.Symbol; }
+    }
+
+    [Storable]
+    private string variableValue;
+    public string VariableValue {
+      get { return variableValue; }
+      set { variableValue = value; }
+    }
+
+    [StorableConstructor]
+    private BinaryFactorVariableTreeNode(bool deserializing) : base(deserializing) { }
+    private BinaryFactorVariableTreeNode(BinaryFactorVariableTreeNode original, Cloner cloner)
+      : base(original, cloner) {
+      variableValue = original.variableValue;
+    }
+    public BinaryFactorVariableTreeNode(BinaryFactorVariable variableSymbol) : base(variableSymbol) { }
+
+    public override bool HasLocalParameters {
+      get { return true; }
+    }
+
+    public override void ResetLocalParameters(IRandom random) {
+      base.ResetLocalParameters(random);
+      variableValue = Symbol.GetVariableValues(VariableName).SampleRandom(random);
+    }
+
+    public override void ShakeLocalParameters(IRandom random, double shakingFactor) {
+      // 50% additive & 50% multiplicative (override of functionality of base class because of a BUG)
+      if (random.NextDouble() < 0.5) {
+        double x = NormalDistributedRandom.NextDouble(random, Symbol.WeightManipulatorMu, Symbol.WeightManipulatorSigma);
+        Weight = Weight + x * shakingFactor;
+      } else {
+        double x = NormalDistributedRandom.NextDouble(random, 1.0, Symbol.MultiplicativeWeightManipulatorSigma);
+        Weight = Weight * x;
+      }
+      if (random.NextDouble() < Symbol.VariableChangeProbability) {
+        var oldName = VariableName;
+        VariableName = Symbol.VariableNames.SampleRandom(random);
+        // reinitialize weights if variable has changed (similar to FactorVariableTreeNode)
+        if (oldName != VariableName)
+          Weight = NormalDistributedRandom.NextDouble(random, Symbol.WeightMu, Symbol.WeightSigma);
+      }
+      variableValue = Symbol.GetVariableValues(VariableName).SampleRandom(random);
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new BinaryFactorVariableTreeNode(this, cloner);
+    }
+
+    public override string ToString() {
+      return base.ToString() + " = " + variableValue;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Constant.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Constant.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Constant.cs	(revision 16337)
@@ -0,0 +1,128 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Constant", "Represents a constant value.")]
+  public sealed class Constant : Symbol {
+    #region Properties
+    [Storable]
+    private double minValue;
+    public double MinValue {
+      get { return minValue; }
+      set {
+        if (value != minValue) {
+          minValue = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double maxValue;
+    public double MaxValue {
+      get { return maxValue; }
+      set {
+        if (value != maxValue) {
+          maxValue = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double manipulatorMu;
+    public double ManipulatorMu {
+      get { return manipulatorMu; }
+      set {
+        if (value != manipulatorMu) {
+          manipulatorMu = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double manipulatorSigma;
+    public double ManipulatorSigma {
+      get { return manipulatorSigma; }
+      set {
+        if (value < 0) throw new ArgumentException();
+        if (value != manipulatorSigma) {
+          manipulatorSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable(DefaultValue = 0.0)]
+    private double multiplicativeManipulatorSigma;
+    public double MultiplicativeManipulatorSigma {
+      get { return multiplicativeManipulatorSigma; }
+      set {
+        if (value < 0) throw new ArgumentException();
+        if (value != multiplicativeManipulatorSigma) {
+          multiplicativeManipulatorSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+
+    private const int minimumArity = 0;
+    private const int maximumArity = 0;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    private Constant(bool deserializing) : base(deserializing) { }
+    private Constant(Constant original, Cloner cloner)
+      : base(original, cloner) {
+      minValue = original.minValue;
+      maxValue = original.maxValue;
+      manipulatorMu = original.manipulatorMu;
+      manipulatorSigma = original.manipulatorSigma;
+      multiplicativeManipulatorSigma = original.multiplicativeManipulatorSigma;
+    }
+    public Constant()
+      : base("Constant", "Represents a constant value.") {
+      manipulatorMu = 0.0;
+      manipulatorSigma = 1.0;
+      multiplicativeManipulatorSigma = 0.03;
+      minValue = -20.0;
+      maxValue = 20.0;
+    }
+
+    public override ISymbolicExpressionTreeNode CreateTreeNode() {
+      return new ConstantTreeNode(this);
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Constant(this, cloner);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ConstantTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ConstantTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ConstantTreeNode.cs	(revision 16337)
@@ -0,0 +1,83 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public sealed class ConstantTreeNode : SymbolicExpressionTreeTerminalNode {
+    public new Constant Symbol {
+      get { return (Constant)base.Symbol; }
+    }
+
+    private double constantValue;
+    [Storable]
+    public double Value {
+      get { return constantValue; }
+      set { constantValue = value; }
+    }
+
+    [StorableConstructor]
+    private ConstantTreeNode(bool deserializing) : base(deserializing) { }
+
+    private ConstantTreeNode(ConstantTreeNode original, Cloner cloner)
+      : base(original, cloner) {
+      constantValue = original.constantValue;
+    }
+
+    private ConstantTreeNode() : base() { }
+    public ConstantTreeNode(Constant constantSymbol) : base(constantSymbol) { }
+
+    public override bool HasLocalParameters {
+      get {
+        return true;
+      }
+    }
+    public override void ResetLocalParameters(IRandom random) {
+      base.ResetLocalParameters(random);
+      var range = Symbol.MaxValue - Symbol.MinValue;
+      Value = random.NextDouble() * range + Symbol.MinValue;
+    }
+
+    public override void ShakeLocalParameters(IRandom random, double shakingFactor) {
+      base.ShakeLocalParameters(random, shakingFactor);
+      // 50% additive & 50% multiplicative
+      if (random.NextDouble() < 0.5) {
+        double x = NormalDistributedRandom.NextDouble(random, Symbol.ManipulatorMu, Symbol.ManipulatorSigma);
+        Value = Value + x * shakingFactor;
+      } else {
+        double x = NormalDistributedRandom.NextDouble(random, 1.0, Symbol.MultiplicativeManipulatorSigma);
+        Value = Value * x;
+      }
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new ConstantTreeNode(this, cloner);
+    }
+
+    public override string ToString() {
+      return constantValue.ToString("E4");
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Cosine.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Cosine.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Cosine.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Cosine", "Symbol that represents the cosine function.")]
+  public sealed class Cosine : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Cosine(bool deserializing) : base(deserializing) { }
+    private Cosine(Cosine original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Cosine(this, cloner);
+    }
+    public Cosine() : base("Cosine", "Symbol that represents the cosine function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/CosineIntegral.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/CosineIntegral.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/CosineIntegral.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("CosineIntegral", "Symbol that represents the cosine integral.")]
+  public sealed class CosineIntegral : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private CosineIntegral(bool deserializing) : base(deserializing) { }
+    private CosineIntegral(CosineIntegral original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new CosineIntegral(this, cloner);
+    }
+    public CosineIntegral() : base("CosineIntegral", "Symbol that represents the cosine integral.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Dawson.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Dawson.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Dawson.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Dawson", "Symbol that represents dawsons integral.")]
+  public sealed class Dawson : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Dawson(bool deserializing) : base(deserializing) { }
+    private Dawson(Dawson original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Dawson(this, cloner);
+    }
+    public Dawson() : base("Dawson", "Symbol that represents dawsons integral.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Derivative.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Derivative.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Derivative.cs	(revision 16337)
@@ -0,0 +1,47 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Derivative", "Represents the derivative over the specified subtree.")]
+  public sealed class Derivative : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Derivative(bool deserializing) : base(deserializing) { }
+    private Derivative(Derivative original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new Derivative(this, cloner); }
+
+    public Derivative() : base("Derivative", "Represents the derivative over the specified subtree.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Division.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Division.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Division.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Division", "Symbol that represents the / operator.")]
+  public sealed class Division : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = byte.MaxValue;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Division(bool deserializing) : base(deserializing) { }
+    private Division(Division original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Division(this, cloner);
+    }
+    public Division() : base("Division", "Symbol that represents the / operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Erf.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Erf.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Erf.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Erf", "Symbol that represents the error function.")]
+  public sealed class Erf : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Erf(bool deserializing) : base(deserializing) { }
+    private Erf(Erf original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Erf(this, cloner);
+    }
+    public Erf() : base("Erf", "Symbol that represents the error function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Exponential.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Exponential.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Exponential.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Exponential", "Symbol that represents the exponential function.")]
+  public sealed class Exponential : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Exponential(bool deserializing) : base(deserializing) { }
+    private Exponential(Exponential original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Exponential(this, cloner);
+    }
+    public Exponential() : base("Exponential", "Symbol that represents the exponential function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ExponentialIntegralEi.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ExponentialIntegralEi.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ExponentialIntegralEi.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("ExponentialIntegralEi", "Symbol that represents the exponential integral (e_i).")]
+  public sealed class ExponentialIntegralEi : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private ExponentialIntegralEi(bool deserializing) : base(deserializing) { }
+    private ExponentialIntegralEi(ExponentialIntegralEi original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new ExponentialIntegralEi(this, cloner);
+    }
+    public ExponentialIntegralEi() : base("ExponentialIntegralEi", "Symbol that represents the exponential integral (e_i).") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FactorVariable.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FactorVariable.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FactorVariable.cs	(revision 16337)
@@ -0,0 +1,78 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("FactorVariable", "Represents a categorical variable (comparable to factors as in R).")]
+  public sealed class FactorVariable : VariableBase {
+    private readonly Dictionary<string, Dictionary<string, int>> variableValues; // for each variable value also store a zero-based index
+    [Storable]
+    public IEnumerable<KeyValuePair<string, Dictionary<string, int>>> VariableValues {
+      get { return variableValues; }
+      set {
+        if(value == null) throw new ArgumentNullException();
+        variableValues.Clear();
+        foreach(var kvp in value) {
+          variableValues.Add(kvp.Key, new Dictionary<string, int>(kvp.Value));
+        }
+      }
+    }
+
+    [StorableConstructor]
+    private FactorVariable(bool deserializing)
+      : base(deserializing) {
+      variableValues = new Dictionary<string, Dictionary<string, int>>();
+    }
+    private FactorVariable(FactorVariable original, Cloner cloner)
+      : base(original, cloner) {
+      variableValues =
+        original.variableValues.ToDictionary(kvp => kvp.Key, kvp => new Dictionary<string, int>(kvp.Value));
+    }
+    public FactorVariable() : this("FactorVariable", "Represents a categorical variable (comparable to factors as in R).") { }
+    public FactorVariable(string name, string description)
+      : base(name, description) {
+      variableValues = new Dictionary<string, Dictionary<string,int>>();
+    }
+
+    public override ISymbolicExpressionTreeNode CreateTreeNode() {
+      return new FactorVariableTreeNode(this);
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new FactorVariable(this, cloner);
+    }
+
+    public IEnumerable<string> GetVariableValues(string variableName) {
+      return variableValues[variableName].Keys;
+    }
+
+    public int GetIndexForValue(string variableName, string variableValue) {
+      return variableValues[variableName][variableValue];
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FactorVariableTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FactorVariableTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FactorVariableTreeNode.cs	(revision 16337)
@@ -0,0 +1,116 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public sealed class FactorVariableTreeNode : SymbolicExpressionTreeTerminalNode, IVariableTreeNode {
+    public new FactorVariable Symbol {
+      get { return (FactorVariable)base.Symbol; }
+    }
+    [Storable]
+    private double[] weights;
+    public double[] Weights {
+      get { return weights; }
+      set { weights = value; }
+    }
+    [Storable]
+    private string variableName;
+    public string VariableName {
+      get { return variableName; }
+      set { variableName = value; }
+    }
+
+    [StorableConstructor]
+    private FactorVariableTreeNode(bool deserializing) : base(deserializing) { }
+    private FactorVariableTreeNode(FactorVariableTreeNode original, Cloner cloner)
+      : base(original, cloner) {
+      variableName = original.variableName;
+      if (original.weights != null) {
+        this.weights = new double[original.Weights.Length];
+        Array.Copy(original.Weights, weights, weights.Length);
+      }
+    }
+
+    public FactorVariableTreeNode(FactorVariable variableSymbol)
+      : base(variableSymbol) {
+    }
+
+    public override bool HasLocalParameters {
+      get { return true; }
+    }
+
+    public override void ResetLocalParameters(IRandom random) {
+      base.ResetLocalParameters(random);
+      variableName = Symbol.VariableNames.SampleRandom(random);
+      weights =
+        Symbol.GetVariableValues(variableName)
+        .Select(_ => NormalDistributedRandom.NextDouble(random, 0, 1)).ToArray();
+    }
+
+    public override void ShakeLocalParameters(IRandom random, double shakingFactor) {
+      // mutate only one randomly selected weight
+      var idx = random.Next(weights.Length);
+      // 50% additive & 50% multiplicative
+      if (random.NextDouble() < 0.5) {
+        double x = NormalDistributedRandom.NextDouble(random, Symbol.WeightManipulatorMu,
+          Symbol.WeightManipulatorSigma);
+        weights[idx] = weights[idx] + x * shakingFactor;
+      } else {
+        double x = NormalDistributedRandom.NextDouble(random, 1.0, Symbol.MultiplicativeWeightManipulatorSigma);
+        weights[idx] = weights[idx] * x;
+      }
+      if (random.NextDouble() < Symbol.VariableChangeProbability) {
+        VariableName = Symbol.VariableNames.SampleRandom(random);
+        if (weights.Length != Symbol.GetVariableValues(VariableName).Count()) {
+          // if the length of the weight array does not match => re-initialize weights
+          weights =
+            Symbol.GetVariableValues(variableName)
+              .Select(_ => NormalDistributedRandom.NextDouble(random, 0, 1))
+              .ToArray();
+        }
+      }
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new FactorVariableTreeNode(this, cloner);
+    }
+
+    public double GetValue(string cat) {
+      return weights[Symbol.GetIndexForValue(VariableName, cat)];
+    }
+
+    public override string ToString() {
+      var weightStr = string.Join("; ",
+        Symbol.GetVariableValues(VariableName).Select(value => value + ": " + GetValue(value).ToString("E4")));
+      return VariableName + " (factor) "
+        + "[" + weightStr + "]";
+    }
+  }
+}
+
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FresnelCosineIntegral.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FresnelCosineIntegral.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FresnelCosineIntegral.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("FresnelCosineIntegral", "Symbol that represents the Fresnel cosine integral.")]
+  public sealed class FresnelCosineIntegral : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private FresnelCosineIntegral(bool deserializing) : base(deserializing) { }
+    private FresnelCosineIntegral(FresnelCosineIntegral original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new FresnelCosineIntegral(this, cloner);
+    }
+    public FresnelCosineIntegral() : base("FresnelCosineIntegral", "Symbol that represents the Fresnel cosine integral.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FresnelSineIntegral.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FresnelSineIntegral.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/FresnelSineIntegral.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("FresnelSineIntegral", "Symbol that represents the Fresnel sine integral.")]
+  public sealed class FresnelSineIntegral : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private FresnelSineIntegral(bool deserializing) : base(deserializing) { }
+    private FresnelSineIntegral(FresnelSineIntegral original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new FresnelSineIntegral(this, cloner);
+    }
+    public FresnelSineIntegral() : base("FresnelSineIntegral", "Symbol that represents the Fresnel sine integral.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Gamma.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Gamma.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Gamma.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Gamma", "Symbol that represents the gamma function.")]
+  public sealed class Gamma : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Gamma(bool deserializing) : base(deserializing) { }
+    private Gamma(Gamma original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Gamma(this, cloner);
+    }
+    public Gamma() : base("Gamma", "Symbol that represents the gamma function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/GreaterThan.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/GreaterThan.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/GreaterThan.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("GreaterThan", "Symbol that represents a greater than relation.")]
+  public sealed class GreaterThan : Symbol {
+    private const int minimumArity = 2;
+    private const int maximumArity = 2;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private GreaterThan(bool deserializing) : base(deserializing) { }
+    private GreaterThan(GreaterThan original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new GreaterThan(this, cloner);
+    }
+    public GreaterThan() : base("GreaterThan", "Symbol that represents a greater than relation.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/HyperbolicCosineIntegral.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/HyperbolicCosineIntegral.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/HyperbolicCosineIntegral.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("HyperbolicCosineIntegral", "Symbol that represents the hyperbolic cosine integral.")]
+  public sealed class HyperbolicCosineIntegral : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private HyperbolicCosineIntegral(bool deserializing) : base(deserializing) { }
+    private HyperbolicCosineIntegral(HyperbolicCosineIntegral original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new HyperbolicCosineIntegral(this, cloner);
+    }
+    public HyperbolicCosineIntegral() : base("HyperbolicCosineIntegral", "Symbol that represents the hyperbolic cosine integral.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/HyperbolicSineIntegral.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/HyperbolicSineIntegral.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/HyperbolicSineIntegral.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("HyperbolicSineIntegral", "Symbol that represents the hyperbolic sine integral.")]
+  public sealed class HyperbolicSineIntegral : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private HyperbolicSineIntegral(bool deserializing) : base(deserializing) { }
+    private HyperbolicSineIntegral(HyperbolicSineIntegral original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new HyperbolicSineIntegral(this, cloner);
+    }
+    public HyperbolicSineIntegral() : base("HyperbolicSineIntegral", "Symbol that represents the hyperbolic sine integral.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ILaggedTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ILaggedTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/ILaggedTreeNode.cs	(revision 16337)
@@ -0,0 +1,28 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public interface ILaggedTreeNode : ISymbolicExpressionTreeNode {
+    int Lag { get; set; }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/IfThenElse.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/IfThenElse.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/IfThenElse.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("IfThenElse", "Symbol that represents a conditional operator.")]
+  public sealed class IfThenElse : Symbol {
+    private const int minimumArity = 3;
+    private const int maximumArity = 3;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private IfThenElse(bool deserializing) : base(deserializing) { }
+    private IfThenElse(IfThenElse original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new IfThenElse(this, cloner);
+    }
+    public IfThenElse() : base("IfThenElse", "Symbol that represents a conditional operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Integral.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Integral.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Integral.cs	(revision 16337)
@@ -0,0 +1,46 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Integral", "Represents the integral over the specified subtree.")]
+  public sealed class Integral : LaggedSymbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Integral(bool deserializing) : base(deserializing) { }
+    private Integral(Integral original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new Integral(this, cloner); }
+
+    public Integral() : base("Integral", "Represents the integral over the specified subtree.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedSymbol.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedSymbol.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedSymbol.cs	(revision 16337)
@@ -0,0 +1,64 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("LaggedSymbol", "Represents a symblol whose evaluation is shifted.")]
+  public abstract class LaggedSymbol : Symbol {
+    [Storable]
+    private int minLag;
+    public virtual int MinLag {
+      get { return minLag; }
+      set { minLag = value; }
+    }
+    [Storable]
+    private int maxLag;
+    public virtual int MaxLag {
+      get { return maxLag; }
+      set { maxLag = value; }
+    }
+
+    [StorableConstructor]
+    protected LaggedSymbol(bool deserializing) : base(deserializing) { }
+    protected LaggedSymbol(LaggedSymbol original, Cloner cloner)
+      : base(original, cloner) {
+      minLag = original.minLag;
+      maxLag = original.maxLag;
+    }
+    protected LaggedSymbol()
+      : base("LaggedSymbol", "Represents a symbol whose evaluation is shifted.") {
+      minLag = -1; maxLag = -1;
+    }
+    protected LaggedSymbol(string name, string description)
+      : base(name, description) {
+      minLag = -1; maxLag = -1;
+    }
+
+    public override ISymbolicExpressionTreeNode CreateTreeNode() {
+      return new LaggedTreeNode(this);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedTreeNode.cs	(revision 16337)
@@ -0,0 +1,70 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public class LaggedTreeNode : SymbolicExpressionTreeNode, ILaggedTreeNode {
+    public new LaggedSymbol Symbol {
+      get { return (LaggedSymbol)base.Symbol; }
+    }
+    [Storable]
+    private int lag;
+    public int Lag {
+      get { return lag; }
+      set { lag = value; }
+    }
+
+    [StorableConstructor]
+    protected LaggedTreeNode(bool deserializing) : base(deserializing) { }
+    protected LaggedTreeNode(LaggedTreeNode original, Cloner cloner)
+      : base(original, cloner) {
+      lag = original.lag;
+    }
+    public LaggedTreeNode(LaggedSymbol timeLagSymbol) : base(timeLagSymbol) { }
+
+    public override bool HasLocalParameters {
+      get { return true; }
+    }
+
+    public override void ResetLocalParameters(IRandom random) {
+      base.ResetLocalParameters(random);
+      lag = random.Next(Symbol.MinLag, Symbol.MaxLag + 1);
+    }
+
+    public override void ShakeLocalParameters(IRandom random, double shakingFactor) {
+      base.ShakeLocalParameters(random, shakingFactor);
+      lag = Math.Min(Symbol.MaxLag, Math.Max(Symbol.MinLag, lag + random.Next(-1, 2)));
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new LaggedTreeNode(this, cloner);
+    }
+
+    public override string ToString() {
+      return base.ToString() + " " + lag.ToString();
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedVariable.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedVariable.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedVariable.cs	(revision 16337)
@@ -0,0 +1,64 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("LaggedVariable", "Represents a variable value with a time offset.")]
+  public class LaggedVariable : VariableBase {
+    [Storable]
+    private int minLag;
+    public int MinLag {
+      get { return minLag; }
+      set { minLag = value; }
+    }
+    [Storable]
+    private int maxLag;
+    public int MaxLag {
+      get { return maxLag; }
+      set { maxLag = value; }
+    }
+    [StorableConstructor]
+    protected LaggedVariable(bool deserializing) : base(deserializing) { }
+    protected LaggedVariable(LaggedVariable original, Cloner cloner)
+      : base(original, cloner) {
+      minLag = original.minLag;
+      maxLag = original.maxLag;
+    }
+    public LaggedVariable() : this("LaggedVariable", "Represents a variable value with a time offset.") { }
+    protected LaggedVariable(string name, string description)
+      : base(name, description) {
+      MinLag = -1;
+      MaxLag = -1;
+    }
+
+    public override ISymbolicExpressionTreeNode CreateTreeNode() {
+      return new LaggedVariableTreeNode(this);
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new LaggedVariable(this, cloner);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedVariableTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedVariableTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LaggedVariableTreeNode.cs	(revision 16337)
@@ -0,0 +1,72 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public sealed class LaggedVariableTreeNode : VariableTreeNodeBase, ILaggedTreeNode {
+    public new LaggedVariable Symbol {
+      get { return (LaggedVariable)base.Symbol; }
+    }
+    [Storable]
+    private int lag;
+    public int Lag {
+      get { return lag; }
+      set { lag = value; }
+    }
+
+    public override bool HasLocalParameters {
+      get { return true; }
+    }
+
+    [StorableConstructor]
+    private LaggedVariableTreeNode(bool deserializing) : base(deserializing) { }
+    private LaggedVariableTreeNode(LaggedVariableTreeNode original, Cloner cloner)
+      : base(original, cloner) {
+      lag = original.lag;
+    }
+
+    public LaggedVariableTreeNode(LaggedVariable variableSymbol) : base(variableSymbol) { }
+
+
+    public override void ResetLocalParameters(IRandom random) {
+      base.ResetLocalParameters(random);
+      lag = random.Next(Symbol.MinLag, Symbol.MaxLag + 1);
+    }
+
+    public override void ShakeLocalParameters(IRandom random, double shakingFactor) {
+      base.ShakeLocalParameters(random, shakingFactor);
+      lag = Math.Min(Symbol.MaxLag, Math.Max(Symbol.MinLag, lag + random.Next(-1, 2)));
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new LaggedVariableTreeNode(this, cloner);
+    }
+
+    public override string ToString() {
+      return base.ToString() +
+        " (t" + (lag > 0 ? "+" : "") + lag + ")";
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LessThan.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LessThan.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/LessThan.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("LessThan", "Symbol that represents a less than relation.")]
+  public sealed class LessThan : Symbol {
+    private const int minimumArity = 2;
+    private const int maximumArity = 2;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private LessThan(bool deserializing) : base(deserializing) { }
+    private LessThan(LessThan original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new LessThan(this, cloner);
+    }
+    public LessThan() : base("LessThan", "Symbol that represents a less than relation.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Logarithm.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Logarithm.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Logarithm.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Logarithm", "Symbol that represents the logarithm function.")]
+  public sealed class Logarithm : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Logarithm(bool deserializing) : base(deserializing) { }
+    private Logarithm(Logarithm original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Logarithm(this, cloner);
+    }
+    public Logarithm() : base("Logarithm", "Symbol that represents the logarithm function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Multiplication.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Multiplication.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Multiplication.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Multiplication", "Symbol that represents the * operator.")]
+  public sealed class Multiplication : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = byte.MaxValue;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Multiplication(bool deserializing) : base(deserializing) { }
+    private Multiplication(Multiplication original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Multiplication(this, cloner);
+    }
+    public Multiplication() : base("Multiplication", "Symbol that represents the * operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Norm.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Norm.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Norm.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Norm", "Symbol that represents the normal distribution function.")]
+  public sealed class Norm : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Norm(bool deserializing) : base(deserializing) { }
+    private Norm(Norm original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Norm(this, cloner);
+    }
+    public Norm() : base("Norm", "Symbol that represents the normal distribution function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Not.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Not.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Not.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Not", "Symbol that represents the boolean NOT operator.")]
+  public sealed class Not : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Not(bool deserializing) : base(deserializing) { }
+    private Not(Not original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Not(this, cloner);
+    }
+    public Not() : base("Not", "Symbol that represents the boolean NOT operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Or.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Or.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Or.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Or", "Symbol that represents the boolean OR operator.")]
+  public sealed class Or : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = byte.MaxValue;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Or(bool deserializing) : base(deserializing) { }
+    private Or(Or original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Or(this, cloner);
+    }
+    public Or() : base("Or", "Symbol that represents the boolean OR operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Power.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Power.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Power.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Power", "Symbol that represents the power function.")]
+  public sealed class Power : Symbol {
+    private const int minimumArity = 2;
+    private const int maximumArity = 2;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Power(bool deserializing) : base(deserializing) { }
+    private Power(Power original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Power(this, cloner);
+    }
+    public Power() : base("Power", "Symbol that represents the power function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Psi.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Psi.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Psi.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Psi", "Symbol that represents the psi function.")]
+  public sealed class Psi : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Psi(bool deserializing) : base(deserializing) { }
+    private Psi(Psi original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Psi(this, cloner);
+    }
+    public Psi() : base("Psi", "Symbol that represents the psi function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Root.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Root.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Root.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Root", "Symbol that represents the n-th root function.")]
+  public sealed class Root : Symbol {
+    private const int minimumArity = 2;
+    private const int maximumArity = 2;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Root(bool deserializing) : base(deserializing) { }
+    private Root(Root original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Root(this, cloner);
+    }
+    public Root() : base("Root", "Symbol that represents the n-th root function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Sine.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Sine.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Sine.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Sine", "Symbol that represents the sine function.")]
+  public sealed class Sine : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Sine(bool deserializing) : base(deserializing) { }
+    private Sine(Sine original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Sine(this, cloner);
+    }
+    public Sine() : base("Sine", "Symbol that represents the sine function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/SineIntegral.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/SineIntegral.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/SineIntegral.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SineIntegral", "Symbol that represents the sine integral.")]
+  public sealed class SineIntegral : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private SineIntegral(bool deserializing) : base(deserializing) { }
+    private SineIntegral(SineIntegral original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SineIntegral(this, cloner);
+    }
+    public SineIntegral() : base("SineIntegral", "Symbol that represents the sine integral.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Square.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Square.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Square.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Square", "Symbol that represents the square function.")]
+  public sealed class Square : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Square(bool deserializing) : base(deserializing) { }
+    private Square(Square original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Square(this, cloner);
+    }
+    public Square() : base("Square", "Symbol that represents the square function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/SquareRoot.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/SquareRoot.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/SquareRoot.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SquareRoot", "Symbol that represents the square root function.")]
+  public sealed class SquareRoot : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private SquareRoot(bool deserializing) : base(deserializing) { }
+    private SquareRoot(SquareRoot original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SquareRoot(this, cloner);
+    }
+    public SquareRoot() : base("SquareRoot", "Symbol that represents the square root function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Subtraction.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Subtraction.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Subtraction.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Subtraction", "Symbol that represents the - operator.")]
+  public sealed class Subtraction : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = byte.MaxValue;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Subtraction(bool deserializing) : base(deserializing) { }
+    private Subtraction(Subtraction original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Subtraction(this, cloner);
+    }
+    public Subtraction() : base("Subtraction", "Symbol that represents the - operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Tangent.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Tangent.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Tangent.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Tangent", "Symbol that represents the tangent trigonometric function.")]
+  public sealed class Tangent : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Tangent(bool deserializing) : base(deserializing) { }
+    private Tangent(Tangent original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Tangent(this, cloner);
+    }
+    public Tangent() : base("Tangent", "Symbol that represents the tangent trigonometric function.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/TimeLag.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/TimeLag.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/TimeLag.cs	(revision 16337)
@@ -0,0 +1,47 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("TimeLag", "Represents a symblol whose evaluation is shifted.")]
+  public sealed class TimeLag : LaggedSymbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = 1;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private TimeLag(bool deserializing) : base(deserializing) { }
+    private TimeLag(TimeLag original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) { return new TimeLag(this, cloner); }
+
+    public TimeLag() : base("TimeLag", "Represents a symbol whose evaluation is shifted.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Variable.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Variable.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Variable.cs	(revision 16337)
@@ -0,0 +1,49 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Variable", "Represents a variable value.")]
+  public sealed class Variable : VariableBase {
+
+    [StorableConstructor]
+    private Variable(bool deserializing)
+      : base(deserializing) {
+    }
+    private Variable(Variable original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    public Variable() : base("Variable", "Represents a variable value.") { }
+    public Variable(string name, string description) : base(name, description) { }
+
+    public override ISymbolicExpressionTreeNode CreateTreeNode() {
+      return new VariableTreeNode(this);
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Variable(this, cloner);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableBase.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableBase.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableBase.cs	(revision 16337)
@@ -0,0 +1,182 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using HeuristicLab.Common;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class VariableBase : Symbol, IVariableSymbol {
+    #region Properties
+    [Storable]
+    private double weightMu;
+    public double WeightMu {
+      get { return weightMu; }
+      set {
+        if (value != weightMu) {
+          weightMu = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double weightSigma;
+    public double WeightSigma {
+      get { return weightSigma; }
+      set {
+        if (weightSigma < 0.0) throw new ArgumentException("Negative sigma is not allowed.");
+        if (value != weightSigma) {
+          weightSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double weightManipulatorMu;
+    public double WeightManipulatorMu {
+      get { return weightManipulatorMu; }
+      set {
+        if (value != weightManipulatorMu) {
+          weightManipulatorMu = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double weightManipulatorSigma;
+    public double WeightManipulatorSigma {
+      get { return weightManipulatorSigma; }
+      set {
+        if (weightManipulatorSigma < 0.0) throw new ArgumentException("Negative sigma is not allowed.");
+        if (value != weightManipulatorSigma) {
+          weightManipulatorSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable(DefaultValue = 0.0)]
+    private double multiplicativeWeightManipulatorSigma;
+    public double MultiplicativeWeightManipulatorSigma {
+      get { return multiplicativeWeightManipulatorSigma; }
+      set {
+        if (multiplicativeWeightManipulatorSigma < 0.0) throw new ArgumentException("Negative sigma is not allowed.");
+        if (value != multiplicativeWeightManipulatorSigma) {
+          multiplicativeWeightManipulatorSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+
+    [Storable(DefaultValue = 1.0)]
+    private double variableChangeProbability;
+
+    public double VariableChangeProbability {
+      get { return variableChangeProbability; }
+      set {
+        if (value < 0 || value > 1.0) throw new ArgumentException("Variable change probability must lie in the interval [0..1]");
+        variableChangeProbability = value;
+      }
+    }
+
+    private List<string> variableNames;
+    [Storable]
+    public IEnumerable<string> VariableNames {
+      get { return variableNames; }
+      set {
+        if (value == null) throw new ArgumentNullException();
+        variableNames.Clear();
+        variableNames.AddRange(value);
+        OnChanged(EventArgs.Empty);
+      }
+    }
+
+    private List<string> allVariableNames;
+    [Storable]
+    public IEnumerable<string> AllVariableNames {
+      get { return allVariableNames; }
+      set {
+        if (value == null) throw new ArgumentNullException();
+        allVariableNames.Clear();
+        allVariableNames.AddRange(value);
+      }
+    }
+
+    public override bool Enabled {
+      get {
+        if (variableNames.Count == 0) return false;
+        return base.Enabled;
+      }
+      set {
+        if (variableNames.Count == 0) base.Enabled = false;
+        else base.Enabled = value;
+      }
+    }
+
+    private const int minimumArity = 0;
+    private const int maximumArity = 0;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+    #endregion
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (allVariableNames == null || (allVariableNames.Count == 0 && variableNames.Count > 0)) {
+        allVariableNames = variableNames;
+      }
+    }
+
+    [StorableConstructor]
+    protected VariableBase(bool deserializing)
+      : base(deserializing) {
+      variableNames = new List<string>();
+      allVariableNames = new List<string>();
+    }
+    protected VariableBase(VariableBase original, Cloner cloner)
+      : base(original, cloner) {
+      weightMu = original.weightMu;
+      weightSigma = original.weightSigma;
+      variableNames = new List<string>(original.variableNames);
+      allVariableNames = new List<string>(original.allVariableNames);
+      weightManipulatorMu = original.weightManipulatorMu;
+      weightManipulatorSigma = original.weightManipulatorSigma;
+      multiplicativeWeightManipulatorSigma = original.multiplicativeWeightManipulatorSigma;
+      variableChangeProbability = original.variableChangeProbability;
+    }
+    protected VariableBase(string name, string description)
+      : base(name, description) {
+      weightMu = 1.0;
+      weightSigma = 1.0;
+      weightManipulatorMu = 0.0;
+      weightManipulatorSigma = 0.05;
+      multiplicativeWeightManipulatorSigma = 0.03;
+      variableChangeProbability = 0.2;
+      variableNames = new List<string>();
+      allVariableNames = new List<string>();
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableCondition.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableCondition.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableCondition.cs	(revision 16337)
@@ -0,0 +1,240 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Variable Condition", "Represents a condition that tests a given variable against a specified threshold.")]
+  public sealed class VariableCondition : Symbol, IVariableSymbol {
+    #region properties
+    [Storable]
+    private double thresholdInitializerMu;
+    public double ThresholdInitializerMu {
+      get { return thresholdInitializerMu; }
+      set {
+        if (value != thresholdInitializerMu) {
+          thresholdInitializerMu = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double thresholdInitializerSigma;
+    public double ThresholdInitializerSigma {
+      get { return thresholdInitializerSigma; }
+      set {
+        if (thresholdInitializerSigma < 0.0) throw new ArgumentException("Negative sigma is not allowed.");
+        if (value != thresholdInitializerSigma) {
+          thresholdInitializerSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+
+    [Storable]
+    private double thresholdManipulatorMu;
+    public double ThresholdManipulatorMu {
+      get { return thresholdManipulatorMu; }
+      set {
+        if (value != thresholdManipulatorMu) {
+          thresholdManipulatorMu = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double thresholdManipulatorSigma;
+    public double ThresholdManipulatorSigma {
+      get { return thresholdManipulatorSigma; }
+      set {
+        if (thresholdManipulatorSigma < 0.0) throw new ArgumentException("Negative sigma is not allowed.");
+        if (value != thresholdManipulatorSigma) {
+          thresholdManipulatorSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+
+    private List<string> variableNames;
+    [Storable]
+    public IEnumerable<string> VariableNames {
+      get { return variableNames; }
+      set {
+        if (value == null) throw new ArgumentNullException();
+        variableNames.Clear();
+        variableNames.AddRange(value);
+        OnChanged(EventArgs.Empty);
+      }
+    }
+
+    private List<string> allVariableNames;
+    [Storable]
+    public IEnumerable<string> AllVariableNames {
+      get { return allVariableNames; }
+      set {
+        if (value == null) throw new ArgumentNullException();
+        allVariableNames.Clear();
+        allVariableNames.AddRange(value);
+      }
+    }
+
+    [Storable]
+    private double slopeInitializerMu;
+    public double SlopeInitializerMu {
+      get { return slopeInitializerMu; }
+      set {
+        if (value != slopeInitializerMu) {
+          slopeInitializerMu = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double slopeInitializerSigma;
+    public double SlopeInitializerSigma {
+      get { return slopeInitializerSigma; }
+      set {
+        if (slopeInitializerSigma < 0.0) throw new ArgumentException("Negative sigma is not allowed.");
+        if (value != slopeInitializerSigma) {
+          slopeInitializerSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+
+    [Storable]
+    private double slopeManipulatorMu;
+    public double SlopeManipulatorMu {
+      get { return slopeManipulatorMu; }
+      set {
+        if (value != slopeManipulatorMu) {
+          slopeManipulatorMu = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+    [Storable]
+    private double slopeManipulatorSigma;
+    public double SlopeManipulatorSigma {
+      get { return slopeManipulatorSigma; }
+      set {
+        if (slopeManipulatorSigma < 0.0) throw new ArgumentException("Negative sigma is not allowed.");
+        if (value != slopeManipulatorSigma) {
+          slopeManipulatorSigma = value;
+          OnChanged(EventArgs.Empty);
+        }
+      }
+    }
+
+    /// <summary>
+    /// Flag to indicate if the interpreter should ignore the slope parameter (introduced for representation of expression trees)
+    /// </summary>
+    [Storable]
+    private bool ignoreSlope;
+    public bool IgnoreSlope {
+      get { return ignoreSlope; }
+      set { ignoreSlope = value; }
+    }
+
+    public override bool Enabled {
+      get {
+        if (variableNames.Count == 0) return false;
+        return base.Enabled;
+      }
+      set {
+        if (variableNames.Count == 0) base.Enabled = false;
+        else base.Enabled = value;
+      }
+    }
+
+    private const int minimumArity = 2;
+    private const int maximumArity = 2;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+    #endregion
+
+    #region persistence and cloning
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+      if (allVariableNames == null || (allVariableNames.Count == 0 && variableNames.Count > 0)) {
+        allVariableNames = variableNames;
+      }
+    }
+
+    [StorableConstructor]
+    private VariableCondition(bool deserializing)
+      : base(deserializing) {
+      variableNames = new List<string>();
+      allVariableNames = new List<string>();
+    }
+    private VariableCondition(VariableCondition original, Cloner cloner)
+      : base(original, cloner) {
+      thresholdInitializerMu = original.thresholdInitializerMu;
+      thresholdInitializerSigma = original.thresholdInitializerSigma;
+      thresholdManipulatorMu = original.thresholdManipulatorMu;
+      thresholdManipulatorSigma = original.thresholdManipulatorSigma;
+
+      variableNames = new List<string>(original.variableNames);
+      allVariableNames = new List<string>(original.allVariableNames);
+
+      slopeInitializerMu = original.slopeInitializerMu;
+      slopeInitializerSigma = original.slopeInitializerSigma;
+      slopeManipulatorMu = original.slopeManipulatorMu;
+      slopeManipulatorSigma = original.slopeManipulatorSigma;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new VariableCondition(this, cloner);
+    }
+    #endregion
+
+    public VariableCondition() : this("Variable Condition", "Represents a condition that tests a given variable.") { }
+    public VariableCondition(string name, string description)
+      : base(name, description) {
+      thresholdInitializerMu = 0.0;
+      thresholdInitializerSigma = 0.1;
+      thresholdManipulatorMu = 0.0;
+      thresholdManipulatorSigma = 0.1;
+
+      variableNames = new List<string>();
+      allVariableNames = new List<string>();
+
+      slopeInitializerMu = 0.0;
+      slopeInitializerSigma = 0.0;
+      slopeManipulatorMu = 0.0;
+      slopeManipulatorSigma = 0.0;
+    }
+
+    public override ISymbolicExpressionTreeNode CreateTreeNode() {
+      return new VariableConditionTreeNode(this);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableConditionTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableConditionTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableConditionTreeNode.cs	(revision 16337)
@@ -0,0 +1,106 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public sealed class VariableConditionTreeNode : SymbolicExpressionTreeNode, IVariableTreeNode {
+    #region properties
+    public new VariableCondition Symbol {
+      get { return (VariableCondition)base.Symbol; }
+    }
+    [Storable]
+    private double threshold;
+    public double Threshold {
+      get { return threshold; }
+      set { threshold = value; }
+    }
+    [Storable]
+    private string variableName;
+    public string VariableName {
+      get { return variableName; }
+      set { variableName = value; }
+    }
+    [Storable]
+    private double slope;
+    public double Slope {
+      get { return slope; }
+      set { slope = value; }
+    }
+    #endregion
+
+    [StorableConstructor]
+    private VariableConditionTreeNode(bool deserializing) : base(deserializing) { }
+    private VariableConditionTreeNode(VariableConditionTreeNode original, Cloner cloner)
+      : base(original, cloner) {
+      threshold = original.threshold;
+      variableName = original.variableName;
+      slope = original.slope;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new VariableConditionTreeNode(this, cloner);
+    }
+
+    public VariableConditionTreeNode(VariableCondition variableConditionSymbol) : base(variableConditionSymbol) { }
+    public override bool HasLocalParameters {
+      get { return true; }
+    }
+
+    public override void ResetLocalParameters(IRandom random) {
+      base.ResetLocalParameters(random);
+      threshold = NormalDistributedRandom.NextDouble(random, Symbol.ThresholdInitializerMu, Symbol.ThresholdInitializerSigma);
+
+#pragma warning disable 612, 618
+      variableName = Symbol.VariableNames.SelectRandom(random);
+#pragma warning restore 612, 618
+
+      slope = NormalDistributedRandom.NextDouble(random, Symbol.SlopeInitializerMu, Symbol.SlopeInitializerSigma);
+    }
+
+    public override void ShakeLocalParameters(IRandom random, double shakingFactor) {
+      base.ShakeLocalParameters(random, shakingFactor);
+      double x = NormalDistributedRandom.NextDouble(random, Symbol.ThresholdManipulatorMu, Symbol.ThresholdManipulatorSigma);
+      threshold = threshold + x * shakingFactor;
+
+#pragma warning disable 612, 618
+      variableName = Symbol.VariableNames.SelectRandom(random);
+#pragma warning restore 612, 618
+
+      x = NormalDistributedRandom.NextDouble(random, Symbol.SlopeManipulatorMu, Symbol.SlopeManipulatorSigma);
+      slope = slope + x * shakingFactor;
+    }
+
+    public override string ToString() {
+      if (slope.IsAlmost(0.0) || Symbol.IgnoreSlope) {
+        return variableName + " < " + threshold.ToString("E4");
+      } else {
+        return variableName + " > " + threshold.ToString("E4") + Environment.NewLine +
+               "slope: " + slope.ToString("E4");
+      }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableTreeNode.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableTreeNode.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableTreeNode.cs	(revision 16337)
@@ -0,0 +1,42 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public sealed class VariableTreeNode : VariableTreeNodeBase {
+    public new Variable Symbol {
+      get { return (Variable)base.Symbol; }
+    }
+    [StorableConstructor]
+    private VariableTreeNode(bool deserializing) : base(deserializing) { }
+    private VariableTreeNode(VariableTreeNode original, Cloner cloner)
+      : base(original, cloner) {
+    }
+    private VariableTreeNode() { }
+    public VariableTreeNode(Variable variableSymbol) : base(variableSymbol) { }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new VariableTreeNode(this, cloner);
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableTreeNodeBase.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableTreeNodeBase.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/VariableTreeNodeBase.cs	(revision 16337)
@@ -0,0 +1,103 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+using HeuristicLab.Random;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  public abstract class VariableTreeNodeBase : SymbolicExpressionTreeTerminalNode, IVariableTreeNode {
+    public new VariableBase Symbol {
+      get { return (VariableBase)base.Symbol; }
+    }
+    [Storable]
+    private double weight;
+    public double Weight {
+      get { return weight; }
+      set { weight = value; }
+    }
+    [Storable]
+    private string variableName;
+    public string VariableName {
+      get { return variableName; }
+      set { variableName = value; }
+    }
+
+    [StorableConstructor]
+    protected VariableTreeNodeBase(bool deserializing) : base(deserializing) { }
+    protected VariableTreeNodeBase(VariableTreeNodeBase original, Cloner cloner)
+      : base(original, cloner) {
+      weight = original.weight;
+      variableName = original.variableName;
+    }
+    protected VariableTreeNodeBase() { }
+    protected VariableTreeNodeBase(VariableBase variableSymbol) : base(variableSymbol) { }
+
+    public override bool HasLocalParameters {
+      get { return true; }
+    }
+
+    public override void ResetLocalParameters(IRandom random) {
+      base.ResetLocalParameters(random);
+      weight = NormalDistributedRandom.NextDouble(random, Symbol.WeightMu, Symbol.WeightSigma);
+
+#pragma warning disable 612, 618
+      variableName = Symbol.VariableNames.SelectRandom(random);
+#pragma warning restore 612, 618
+    }
+
+    public override void ShakeLocalParameters(IRandom random, double shakingFactor) {
+      base.ShakeLocalParameters(random, shakingFactor);
+
+      // 50% additive & 50% multiplicative (TODO: BUG in if statement below -> fix in HL 4.0!)
+      if (random.NextDouble() < 0) {
+        double x = NormalDistributedRandom.NextDouble(random, Symbol.WeightManipulatorMu, Symbol.WeightManipulatorSigma);
+        weight = weight + x * shakingFactor;
+      } else {
+        double x = NormalDistributedRandom.NextDouble(random, 1.0, Symbol.MultiplicativeWeightManipulatorSigma);
+        weight = weight * x;
+      }
+
+      if (Symbol.VariableChangeProbability >= 1.0) {
+        // old behaviour for backwards compatibility
+        #region Backwards compatible code, remove with 3.4
+#pragma warning disable 612, 618
+        variableName = Symbol.VariableNames.SelectRandom(random);
+#pragma warning restore 612, 618
+        #endregion
+      } else if (random.NextDouble() < Symbol.VariableChangeProbability) {
+        var oldName = variableName;
+        variableName = Symbol.VariableNames.SampleRandom(random);
+        if (oldName != variableName) {
+          // re-initialize weight if the variable is changed
+          weight = NormalDistributedRandom.NextDouble(random, Symbol.WeightMu, Symbol.WeightSigma);
+        }
+      }
+    }
+
+    public override string ToString() {
+      if (weight.IsAlmost(1.0)) return variableName;
+      else return weight.ToString("E4") + " " + variableName;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Xor.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Xor.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Symbols/Xor.cs	(revision 16337)
@@ -0,0 +1,48 @@
+#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("Xor", "Symbol that represents the boolean XOR operator.")]
+  public sealed class Xor : Symbol {
+    private const int minimumArity = 1;
+    private const int maximumArity = byte.MaxValue;
+
+    public override int MinimumArity {
+      get { return minimumArity; }
+    }
+    public override int MaximumArity {
+      get { return maximumArity; }
+    }
+
+    [StorableConstructor]
+    private Xor(bool deserializing) : base(deserializing) { }
+    private Xor(Xor original, Cloner cloner) : base(original, cloner) { }
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new Xor(this, cloner);
+    }
+    public Xor() : base("Xor", "Symbol that represents the boolean XOR operator.") { }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Transformations/SymbolicExpressionTreeBacktransformator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Transformations/SymbolicExpressionTreeBacktransformator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Transformations/SymbolicExpressionTreeBacktransformator.cs	(revision 16337)
@@ -0,0 +1,97 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public class SymbolicExpressionTreeBacktransformator : IModelBacktransformator {
+    private readonly ITransformationMapper<ISymbolicExpressionTreeNode> transformationMapper;
+
+    public SymbolicExpressionTreeBacktransformator(ITransformationMapper<ISymbolicExpressionTreeNode> transformationMapper) {
+      this.transformationMapper = transformationMapper;
+    }
+
+    public ISymbolicDataAnalysisModel Backtransform(ISymbolicDataAnalysisModel model, IEnumerable<ITransformation> transformations, string targetVariable) {
+      var symbolicModel = (ISymbolicDataAnalysisModel)model.Clone();
+
+      foreach (var transformation in transformations.Reverse()) {
+        ApplyBacktransformation(transformation, symbolicModel.SymbolicExpressionTree, targetVariable);
+      }
+
+      return symbolicModel;
+    }
+
+    private void ApplyBacktransformation(ITransformation transformation, ISymbolicExpressionTree symbolicExpressionTree, string targetVariable) {
+      if (transformation.Column != targetVariable) {
+        var variableNodes = symbolicExpressionTree.IterateNodesBreadth()
+          .OfType<VariableTreeNode>()
+          .Where(n => n.VariableName == transformation.Column);
+        ApplyRegularBacktransformation(transformation, variableNodes);
+      } else if (!(transformation is CopyColumnTransformation)) {
+        ApplyInverseBacktransformation(transformation, symbolicExpressionTree);
+      }
+    }
+
+    private void ApplyRegularBacktransformation(ITransformation transformation, IEnumerable<VariableTreeNode> variableNodes) {
+      foreach (var variableNode in variableNodes) {
+        // generate new subtrees because same subtree cannot be added more than once
+        var transformationTree = transformationMapper.GenerateModel(transformation);
+        SwapVariableWithTree(variableNode, transformationTree);
+      }
+    }
+
+    private void ApplyInverseBacktransformation(ITransformation transformation, ISymbolicExpressionTree symbolicExpressionTree) {
+      var startSymbol = symbolicExpressionTree.Root.GetSubtree(0);
+      var modelTree = startSymbol.GetSubtree(0);
+      startSymbol.RemoveSubtree(0);
+
+      var transformationTree = transformationMapper.GenerateInverseModel(transformation);
+      var variableNode = transformationTree.IterateNodesBreadth()
+        .OfType<VariableTreeNode>()
+        .Single(n => n.VariableName == transformation.Column);
+
+      SwapVariableWithTree(variableNode, modelTree);
+
+      startSymbol.AddSubtree(transformationTree);
+    }
+
+    private void SwapVariableWithTree(VariableTreeNode variableNode, ISymbolicExpressionTreeNode treeNode) {
+      var parent = variableNode.Parent;
+      int index = parent.IndexOfSubtree(variableNode);
+      parent.RemoveSubtree(index);
+
+      if (!variableNode.Weight.IsAlmost(1.0))
+        treeNode = CreateNodeFromWeight(treeNode, variableNode);
+
+      parent.InsertSubtree(index, treeNode);
+    }
+
+    private ISymbolicExpressionTreeNode CreateNodeFromWeight(ISymbolicExpressionTreeNode transformationTree, VariableTreeNode variableNode) {
+      var multiplicationNode = new SymbolicExpressionTreeNode(new Multiplication());
+      multiplicationNode.AddSubtree(new ConstantTreeNode(new Constant()) { Value = variableNode.Weight });
+      multiplicationNode.AddSubtree(transformationTree);
+      return multiplicationNode;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Transformations/TransformationToSymbolicTreeMapper.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Transformations/TransformationToSymbolicTreeMapper.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/Transformations/TransformationToSymbolicTreeMapper.cs	(revision 16337)
@@ -0,0 +1,294 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public class TransformationToSymbolicTreeMapper : ITransformationMapper<ISymbolicExpressionTreeNode> {
+    private ITransformation transformation;
+    private string column;
+
+    #region ITransformationMapper<ISymbolicExpressionTree> Members
+
+    public ISymbolicExpressionTreeNode GenerateModel(ITransformation transformation) {
+      InitComponents(transformation);
+
+      if (transformation is LinearTransformation) {
+        return GenerateModelForLinearTransformation();
+      } else if (transformation is ExponentialTransformation) {
+        return GenerateModelForExponentialTransformation();
+      } else if (transformation is LogarithmicTransformation) {
+        return GenerateModelForLogarithmicTransformation();
+      } else if (transformation is PowerTransformation) {
+        return GenerateModelForPowerTransformation();
+      } else if (transformation is ReciprocalTransformation) {
+        return GenerateModelForReciprocalTransformation();
+      } else if (transformation is ShiftStandardDistributionTransformation) {
+        return GenerateModelForShiftStandardDistributionTransformation();
+      } else if (transformation is CopyColumnTransformation) {
+        return GenerateTreeNodeForCopyColumnTransformation();
+      }
+      throw new NotImplementedException();
+    }
+
+    public ISymbolicExpressionTreeNode GenerateInverseModel(ITransformation transformation) {
+      InitComponents(transformation);
+
+      if (transformation is LinearTransformation) {
+        return GenerateInverseModelForLinearTransformation();
+      } else if (transformation is ExponentialTransformation) {
+        return GenerateInverseModelForExponentialTransformation();
+      } else if (transformation is LogarithmicTransformation) {
+        return GenerateInverseModelForLogarithmicTransformation();
+      } else if (transformation is PowerTransformation) {
+        return GenerateInverseModelForPowerTransformation();
+      } else if (transformation is ReciprocalTransformation) {
+        return GenerateInverseModelForReciprocalTransformation();
+      } else if (transformation is ShiftStandardDistributionTransformation) {
+        GenerateInverseModelForShiftStandardDistributionTransformation();
+      } else if (transformation is CopyColumnTransformation) {
+        return GenerateTreeNodeForCopyColumnTransformation();
+      }
+
+      throw new NotImplementedException();
+    }
+
+    #endregion
+
+    // helper
+
+    private ISymbolicExpressionTreeNode GenerateModelForLinearTransformation() {
+      var linearTransformation = (LinearTransformation)transformation;
+      var kValue = linearTransformation.Multiplier;
+      var dValue = linearTransformation.Addend;
+
+      // k * x
+      var multiplicationNode = new Multiplication().CreateTreeNode();
+      var kNode = CreateConstantTreeNode("k", kValue);
+      var xNode = CreateVariableTreeNode(column, "x");
+      multiplicationNode.AddSubtree(kNode);
+      multiplicationNode.AddSubtree(xNode);
+
+      // ( k * x ) + d
+      var additionNode = new Addition().CreateTreeNode();
+      var dNode = CreateConstantTreeNode("d", dValue);
+      additionNode.AddSubtree(multiplicationNode);
+      additionNode.AddSubtree(dNode);
+
+      return additionNode;
+    }
+
+    private ISymbolicExpressionTreeNode GenerateInverseModelForLinearTransformation() {
+      var linearTransformation = (LinearTransformation)transformation;
+      var kValue = linearTransformation.Multiplier;
+      var dValue = linearTransformation.Addend;
+
+      // x - d
+      var substractionNode = new Subtraction().CreateTreeNode();
+      var dNode = CreateConstantTreeNode("d", dValue);
+      var xNode = CreateVariableTreeNode(column, "x");
+      substractionNode.AddSubtree(xNode);
+      substractionNode.AddSubtree(dNode);
+
+      // ( x - d ) / k
+      var divisionNode = new Division().CreateTreeNode();
+      var kNode = CreateConstantTreeNode("k", kValue);
+      divisionNode.AddSubtree(substractionNode);
+      divisionNode.AddSubtree(kNode);
+
+      return divisionNode;
+    }
+
+
+    private ISymbolicExpressionTreeNode GenerateModelForExponentialTransformation() {
+      var exponentialTransformation = (ExponentialTransformation)transformation;
+      var bValue = exponentialTransformation.Base;
+
+      return GenTreePow_b_x(bValue);
+    }
+
+    private ISymbolicExpressionTreeNode GenerateInverseModelForExponentialTransformation() {
+      var exponentialTransformation = (ExponentialTransformation)transformation;
+      var bValue = exponentialTransformation.Base;
+
+      return GenTreeLog_x_b(bValue);
+    }
+
+
+    private ISymbolicExpressionTreeNode GenerateModelForLogarithmicTransformation() {
+      var logarithmicTransformation = (LogarithmicTransformation)transformation;
+      var bValue = logarithmicTransformation.Base;
+
+      return GenTreeLog_x_b(bValue);
+    }
+
+    private ISymbolicExpressionTreeNode GenerateInverseModelForLogarithmicTransformation() {
+      var logarithmicTransformation = (LogarithmicTransformation)transformation;
+      var bValue = logarithmicTransformation.Base;
+
+      return GenTreePow_b_x(bValue);
+    }
+
+
+    private ISymbolicExpressionTreeNode GenerateModelForPowerTransformation() {
+      var powerTransformation = (PowerTransformation)transformation;
+      var expValue = powerTransformation.Exponent;
+
+      // x ^ exp
+      var powerNode = new Power().CreateTreeNode();
+      var xNode = CreateVariableTreeNode(column, "x");
+      var expNode = CreateConstantTreeNode("exp", expValue);
+      powerNode.AddSubtree(xNode);
+      powerNode.AddSubtree(expNode);
+
+      return powerNode;
+    }
+
+    private ISymbolicExpressionTreeNode GenerateInverseModelForPowerTransformation() {
+      var powerTransformation = (PowerTransformation)transformation;
+      var expValue = powerTransformation.Exponent;
+
+      // rt(x, b)
+      var rootNode = new Root().CreateTreeNode();
+      var xNode = CreateVariableTreeNode(column, "x");
+      var bNode = CreateConstantTreeNode("b", expValue);
+      rootNode.AddSubtree(xNode);
+      rootNode.AddSubtree(bNode);
+
+      return rootNode;
+    }
+
+
+    private ISymbolicExpressionTreeNode GenerateModelForReciprocalTransformation() {
+      return GenTreeDiv_1_x();
+    }
+
+    private ISymbolicExpressionTreeNode GenerateInverseModelForReciprocalTransformation() {
+      return GenTreeDiv_1_x();
+    }
+
+
+    private ISymbolicExpressionTreeNode GenerateModelForShiftStandardDistributionTransformation() {
+      var shiftStandardDistributionTransformation = (ShiftStandardDistributionTransformation)transformation;
+      var m_orgValue = shiftStandardDistributionTransformation.OriginalMean;
+      var s_orgValue = shiftStandardDistributionTransformation.OriginalStandardDeviation;
+      var m_tarValue = shiftStandardDistributionTransformation.Mean;
+      var s_tarValue = shiftStandardDistributionTransformation.StandardDeviation;
+
+      return GenTreeShiftStdDist(column, m_orgValue, s_orgValue, m_tarValue, s_tarValue);
+    }
+
+    private ISymbolicExpressionTreeNode GenerateInverseModelForShiftStandardDistributionTransformation() {
+      var shiftStandardDistributionTransformation = (ShiftStandardDistributionTransformation)transformation;
+      var m_orgValue = shiftStandardDistributionTransformation.OriginalMean;
+      var s_orgValue = shiftStandardDistributionTransformation.OriginalStandardDeviation;
+      var m_tarValue = shiftStandardDistributionTransformation.Mean;
+      var s_tarValue = shiftStandardDistributionTransformation.StandardDeviation;
+
+      return GenTreeShiftStdDist(column, m_tarValue, s_tarValue, m_orgValue, s_orgValue);
+    }
+
+    private ISymbolicExpressionTreeNode GenerateTreeNodeForCopyColumnTransformation() {
+      var copyColumnTransformation = (CopyColumnTransformation)transformation;
+      var copiedColumnName = copyColumnTransformation.CopiedColumnName;
+
+      return CreateVariableTreeNode(copiedColumnName, copiedColumnName + "(original)");
+    }
+
+    // helper's helper:
+
+    private ISymbolicExpressionTreeNode GenTreeLog_x_b(double b) {
+      // log(x, b)
+      var logNode = new Logarithm().CreateTreeNode();
+      var bNode = CreateConstantTreeNode("b", b);
+      var xNode = CreateVariableTreeNode(column, "x");
+      logNode.AddSubtree(xNode);
+      logNode.AddSubtree(bNode);
+
+      return logNode;
+    }
+
+    private ISymbolicExpressionTreeNode GenTreePow_b_x(double b) {
+      // b ^ x
+      var powerNode = new Power().CreateTreeNode();
+      var bNode = CreateConstantTreeNode("b", b);
+      var xNode = CreateVariableTreeNode(column, "x");
+      powerNode.AddSubtree(bNode);
+      powerNode.AddSubtree(xNode);
+
+      return powerNode;
+    }
+
+    private ISymbolicExpressionTreeNode GenTreeDiv_1_x() {
+      // 1 / x
+      var divNode = new Division().CreateTreeNode();
+      var oneNode = CreateConstantTreeNode("1", 1.0);
+      var xNode = CreateVariableTreeNode(column, "x");
+      divNode.AddSubtree(oneNode);
+      divNode.AddSubtree(xNode);
+
+      return divNode;
+    }
+
+    private ISymbolicExpressionTreeNode GenTreeShiftStdDist(string variable, double m_org, double s_org, double m_tar, double s_tar) {
+      // x - m_org
+      var substractionNode = new Subtraction().CreateTreeNode();
+      var xNode = CreateVariableTreeNode(variable, "x");
+      var m_orgNode = CreateConstantTreeNode("m_org", m_org);
+      substractionNode.AddSubtree(xNode);
+      substractionNode.AddSubtree(m_orgNode);
+
+      // (x - m_org) / s_org
+      var divisionNode = new Division().CreateTreeNode();
+      var s_orgNode = CreateConstantTreeNode("s_org", s_org);
+      divisionNode.AddSubtree(substractionNode);
+      divisionNode.AddSubtree(s_orgNode);
+
+      // ((x - m_org) / s_org ) * s_tar
+      var multiplicationNode = new Multiplication().CreateTreeNode();
+      var s_tarNode = CreateConstantTreeNode("s_tar", s_tar);
+      multiplicationNode.AddSubtree(divisionNode);
+      multiplicationNode.AddSubtree(s_tarNode);
+
+      // ((x - m_org) / s_org ) * s_tar + m_tar
+      var additionNode = new Addition().CreateTreeNode();
+      var m_tarNode = CreateConstantTreeNode("m_tar", m_tar);
+      additionNode.AddSubtree(multiplicationNode);
+      additionNode.AddSubtree(m_tarNode);
+
+      return additionNode;
+    }
+
+    private ConstantTreeNode CreateConstantTreeNode(string description, double value) {
+      return new ConstantTreeNode(new Constant()) { Value = value };
+    }
+
+    private VariableTreeNode CreateVariableTreeNode(string name, string description) {
+      return new VariableTreeNode(new Variable(name, description)) { VariableName = name, Weight = 1.0 };
+    }
+
+    private void InitComponents(ITransformation transformation) {
+      this.transformation = transformation;
+      column = transformation.Column;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeBottomUpSimilarityCalculator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeBottomUpSimilarityCalculator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeBottomUpSimilarityCalculator.cs	(revision 16337)
@@ -0,0 +1,242 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization.Operators;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+using NodeMap = System.Collections.Generic.Dictionary<HeuristicLab.Encodings.SymbolicExpressionTreeEncoding.ISymbolicExpressionTreeNode, HeuristicLab.Encodings.SymbolicExpressionTreeEncoding.ISymbolicExpressionTreeNode>;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicExpressionTreeBottomUpSimilarityCalculator", "A similarity calculator which uses the tree bottom-up distance as a similarity metric.")]
+  public class SymbolicExpressionTreeBottomUpSimilarityCalculator : SolutionSimilarityCalculator {
+    private readonly HashSet<string> commutativeSymbols = new HashSet<string> { "Addition", "Multiplication", "Average", "And", "Or", "Xor" };
+
+    public SymbolicExpressionTreeBottomUpSimilarityCalculator() { }
+    protected override bool IsCommutative { get { return true; } }
+
+    public bool MatchConstantValues { get; set; }
+    public bool MatchVariableWeights { get; set; }
+
+    [StorableConstructor]
+    protected SymbolicExpressionTreeBottomUpSimilarityCalculator(bool deserializing)
+      : base(deserializing) {
+    }
+
+    protected SymbolicExpressionTreeBottomUpSimilarityCalculator(SymbolicExpressionTreeBottomUpSimilarityCalculator original, Cloner cloner)
+      : base(original, cloner) {
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicExpressionTreeBottomUpSimilarityCalculator(this, cloner);
+    }
+
+    #region static methods
+    private static ISymbolicExpressionTreeNode ActualRoot(ISymbolicExpressionTree tree) {
+      return tree.Root.GetSubtree(0).GetSubtree(0);
+    }
+
+    public static double CalculateSimilarity(ISymbolicExpressionTree t1, ISymbolicExpressionTree t2, bool strict = false) {
+      return CalculateSimilarity(ActualRoot(t1), ActualRoot(t2), strict);
+    }
+
+    public static double CalculateSimilarity(ISymbolicExpressionTreeNode n1, ISymbolicExpressionTreeNode n2, bool strict = false) {
+      var calculator = new SymbolicExpressionTreeBottomUpSimilarityCalculator { MatchConstantValues = strict, MatchVariableWeights = strict };
+      return CalculateSimilarity(n1, n2, strict);
+    }
+
+    public static Dictionary<ISymbolicExpressionTreeNode, ISymbolicExpressionTreeNode> ComputeBottomUpMapping(ISymbolicExpressionTree t1, ISymbolicExpressionTree t2, bool strict = false) {
+      return ComputeBottomUpMapping(ActualRoot(t1), ActualRoot(t2), strict);
+    }
+
+    public static Dictionary<ISymbolicExpressionTreeNode, ISymbolicExpressionTreeNode> ComputeBottomUpMapping(ISymbolicExpressionTreeNode n1, ISymbolicExpressionTreeNode n2, bool strict = false) {
+      var calculator = new SymbolicExpressionTreeBottomUpSimilarityCalculator { MatchConstantValues = strict, MatchVariableWeights = strict };
+      return calculator.ComputeBottomUpMapping(n1, n2);
+    }
+    #endregion
+
+    public double CalculateSimilarity(ISymbolicExpressionTree t1, ISymbolicExpressionTree t2) {
+      return CalculateSimilarity(t1, t2, out Dictionary<ISymbolicExpressionTreeNode, ISymbolicExpressionTreeNode> map);
+    }
+
+    public double CalculateSimilarity(ISymbolicExpressionTree t1, ISymbolicExpressionTree t2, out NodeMap map) {
+      if (t1 == t2) {
+        map = null;
+        return 1;
+      }
+      map = ComputeBottomUpMapping(t1, t2);
+      return 2.0 * map.Count / (t1.Length + t2.Length - 4); // -4 for skipping root and start symbols in the two trees
+    }
+
+    public override double CalculateSolutionSimilarity(IScope leftSolution, IScope rightSolution) {
+      if (leftSolution == rightSolution)
+        return 1.0;
+
+      var t1 = leftSolution.Variables[SolutionVariableName].Value as ISymbolicExpressionTree;
+      var t2 = rightSolution.Variables[SolutionVariableName].Value as ISymbolicExpressionTree;
+
+      if (t1 == null || t2 == null)
+        throw new ArgumentException("Cannot calculate similarity when one of the arguments is null.");
+
+      var similarity = CalculateSimilarity(t1, t2);
+      if (similarity > 1.0)
+        throw new Exception("Similarity value cannot be greater than 1");
+
+      return similarity;
+    }
+
+    public Dictionary<ISymbolicExpressionTreeNode, ISymbolicExpressionTreeNode> ComputeBottomUpMapping(ISymbolicExpressionTree t1, ISymbolicExpressionTree t2) {
+      return ComputeBottomUpMapping(t1.Root.GetSubtree(0).GetSubtree(0), t2.Root.GetSubtree(0).GetSubtree(0));
+    }
+
+    public Dictionary<ISymbolicExpressionTreeNode, ISymbolicExpressionTreeNode> ComputeBottomUpMapping(ISymbolicExpressionTreeNode n1, ISymbolicExpressionTreeNode n2) {
+      var compactedGraph = Compact(n1, n2);
+
+      IEnumerable<ISymbolicExpressionTreeNode> Subtrees(ISymbolicExpressionTreeNode node, bool commutative) {
+        var subtrees = node.IterateNodesPrefix();
+        return commutative ? subtrees.OrderBy(x => compactedGraph[x].Hash) : subtrees;
+      }
+
+      var nodes1 = n1.IterateNodesPostfix().OrderByDescending(x => x.GetLength()); // by descending length so that largest subtrees are mapped first
+      var nodes2 = (List<ISymbolicExpressionTreeNode>)n2.IterateNodesPostfix();
+
+      var forward = new NodeMap();
+      var reverse = new NodeMap();
+
+      foreach (ISymbolicExpressionTreeNode v in nodes1) {
+        if (forward.ContainsKey(v))
+          continue;
+
+        var kv = compactedGraph[v];
+        var commutative = v.SubtreeCount > 1 && commutativeSymbols.Contains(kv.Label);
+
+        foreach (ISymbolicExpressionTreeNode w in nodes2) {
+          if (w.GetLength() != kv.Length || w.GetDepth() != kv.Depth || reverse.ContainsKey(w) || compactedGraph[w] != kv)
+            continue;
+
+          // map one whole subtree to the other
+          foreach (var t in Subtrees(v, commutative).Zip(Subtrees(w, commutative), Tuple.Create)) {
+            forward[t.Item1] = t.Item2;
+            reverse[t.Item2] = t.Item1;
+          }
+
+          break;
+        }
+      }
+
+      return forward;
+    }
+
+    /// <summary>
+    /// Creates a compact representation of the two trees as a directed acyclic graph
+    /// </summary>
+    /// <param name="n1">The root of the first tree</param>
+    /// <param name="n2">The root of the second tree</param>
+    /// <returns>The compacted DAG representing the two trees</returns>
+    private Dictionary<ISymbolicExpressionTreeNode, GraphNode> Compact(ISymbolicExpressionTreeNode n1, ISymbolicExpressionTreeNode n2) {
+      var nodeMap = new Dictionary<ISymbolicExpressionTreeNode, GraphNode>(); // K
+      var labelMap = new Dictionary<string, GraphNode>(); // L
+
+      var nodes = n1.IterateNodesPostfix().Concat(n2.IterateNodesPostfix()); // the disjoint union F
+      var graph = new List<GraphNode>();
+
+      IEnumerable<GraphNode> Subtrees(GraphNode g, bool commutative) {
+        var subtrees = g.SymbolicExpressionTreeNode.Subtrees.Select(x => nodeMap[x]);
+        return commutative ? subtrees.OrderBy(x => x.Hash) : subtrees;
+      }
+
+      foreach (var node in nodes) {
+        var label = GetLabel(node);
+
+        if (node.SubtreeCount == 0) {
+          if (!labelMap.ContainsKey(label)) {
+            labelMap[label] = new GraphNode(node, label);
+          }
+          nodeMap[node] = labelMap[label];
+        } else {
+          var v = new GraphNode(node, label);
+          bool found = false;
+          var commutative = node.SubtreeCount > 1 && commutativeSymbols.Contains(label);
+
+          var vv = Subtrees(v, commutative);
+
+          foreach (var w in graph) {
+            if (v.Depth != w.Depth || v.SubtreeCount != w.SubtreeCount || v.Length != w.Length || v.Label != w.Label) {
+              continue;
+            }
+
+            var ww = Subtrees(w, commutative);
+            found = vv.SequenceEqual(ww);
+
+            if (found) {
+              nodeMap[node] = w;
+              break;
+            }
+          }
+          if (!found) {
+            nodeMap[node] = v;
+            graph.Add(v);
+          }
+        }
+      }
+      return nodeMap;
+    }
+
+    private string GetLabel(ISymbolicExpressionTreeNode node) {
+      if (node.SubtreeCount > 0)
+        return node.Symbol.Name;
+
+      if (node is ConstantTreeNode constant)
+        return MatchConstantValues ? constant.Value.ToString(CultureInfo.InvariantCulture) : constant.Symbol.Name;
+
+      if (node is VariableTreeNode variable)
+        return MatchVariableWeights ? variable.Weight + variable.VariableName : variable.VariableName;
+
+      return node.ToString();
+    }
+
+    private class GraphNode {
+      private GraphNode() { }
+
+      public GraphNode(ISymbolicExpressionTreeNode node, string label) {
+        SymbolicExpressionTreeNode = node;
+        Label = label;
+        Hash = GetHashCode();
+        Depth = node.GetDepth();
+        Length = node.GetLength();
+      }
+
+      public int Hash { get; }
+      public ISymbolicExpressionTreeNode SymbolicExpressionTreeNode { get; }
+      public string Label { get; }
+      public int Depth { get; }
+      public int SubtreeCount { get { return SymbolicExpressionTreeNode.SubtreeCount; } }
+      public int Length { get; }
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeCanonicalSorter.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeCanonicalSorter.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeCanonicalSorter.cs	(revision 16337)
@@ -0,0 +1,30 @@
+﻿
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public class SymbolicExpressionTreeCanonicalSorter {
+    private readonly HashSet<Type> nonSymmetricSymbols = new HashSet<Type> { typeof(Subtraction), typeof(Division) };
+
+    public void SortSubtrees(ISymbolicExpressionTree tree) {
+      SortSubtrees(tree.Root);
+    }
+
+    public void SortSubtrees(ISymbolicExpressionTreeNode node) {
+      if (node.SubtreeCount == 0) return;
+      var subtrees = node.Subtrees as List<ISymbolicExpressionTreeNode> ?? node.Subtrees.ToList();
+      if (IsSymmetric(node.Symbol)) {
+        var comparer = new SymbolicExpressionTreeNodeComparer();
+        subtrees.Sort(comparer);
+      }
+      foreach (var s in subtrees)
+        SortSubtrees(s);
+    }
+
+    private bool IsSymmetric(ISymbol s) {
+      return !nonSymmetricSymbols.Contains(s.GetType());
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeEqualityComparer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeEqualityComparer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeEqualityComparer.cs	(revision 16337)
@@ -0,0 +1,18 @@
+﻿using System;
+using System.Collections.Generic;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public class SymbolicExpressionTreeEqualityComparer : IEqualityComparer<ISymbolicExpressionTree> {
+    public SymbolicExpressionTreeNodeEqualityComparer SimilarityComparer { get; set; }
+
+    public bool Equals(ISymbolicExpressionTree a, ISymbolicExpressionTree b) {
+      if (SimilarityComparer == null) throw new Exception("SimilarityComparer needs to be initialized first.");
+      return a.Length == b.Length && SymbolicExpressionTreeMatching.Match(a.Root, b.Root, SimilarityComparer) == Math.Min(a.Length, b.Length);
+    }
+
+    public int GetHashCode(ISymbolicExpressionTree tree) {
+      return (tree.Length << 8) % 12345;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeMatching.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeMatching.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeMatching.cs	(revision 16337)
@@ -0,0 +1,125 @@
+﻿#region License Information
+
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#endregion
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+//using HeuristicLab.EvolutionTracking;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  public static class SymbolicExpressionTreeMatching {
+    public static bool ContainsSubtree(this ISymbolicExpressionTreeNode root, ISymbolicExpressionTreeNode subtree, SymbolicExpressionTreeNodeEqualityComparer comparer) {
+      return FindMatches(root, subtree, comparer).Any();
+    }
+    public static IEnumerable<ISymbolicExpressionTreeNode> FindMatches(ISymbolicExpressionTree tree, ISymbolicExpressionTreeNode subtree, SymbolicExpressionTreeNodeEqualityComparer comparer) {
+      return FindMatches(tree.Root, subtree, comparer);
+    }
+
+    public static IEnumerable<ISymbolicExpressionTreeNode> FindMatches(ISymbolicExpressionTreeNode root, ISymbolicExpressionTreeNode subtree, SymbolicExpressionTreeNodeEqualityComparer comp) {
+      var fragmentLength = subtree.GetLength();
+      // below, we use ">=" for Match(n, subtree, comp) >= fragmentLength because in case of relaxed conditions, 
+      // we can have multiple matches of the same node
+
+      return root.IterateNodesBreadth().Where(n => n.GetLength() >= fragmentLength && Match(n, subtree, comp) == fragmentLength);
+    }
+
+    ///<summary>
+    /// Finds the longest common subsequence in quadratic time and linear space
+    /// Variant of:
+    /// D. S. Hirschberg. A linear space algorithm for or computing maximal common subsequences. 1975.
+    /// http://dl.acm.org/citation.cfm?id=360861
+    /// </summary>
+    /// <returns>Number of pairs that were matched</returns>
+    public static int Match(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b, ISymbolicExpressionTreeNodeSimilarityComparer comp) {
+      if (!comp.Equals(a, b)) return 0;
+      int m = a.SubtreeCount;
+      int n = b.SubtreeCount;
+      if (m == 0 || n == 0) return 1;
+      var matrix = new int[m + 1, n + 1];
+      for (int i = 1; i <= m; ++i) {
+        var ai = a.GetSubtree(i - 1);
+        for (int j = 1; j <= n; ++j) {
+          var bj = b.GetSubtree(j - 1);
+          int match = Match(ai, bj, comp);
+          matrix[i, j] = Math.Max(Math.Max(matrix[i, j - 1], matrix[i - 1, j]), matrix[i - 1, j - 1] + match);
+        }
+      }
+      return matrix[m, n] + 1;
+    }
+
+    /// <summary>
+    /// Calculates the difference between two symbolic expression trees.
+    /// </summary>
+    /// <param name="tree">The first symbolic expression tree</param>
+    /// <param name="other">The second symbolic expression tree</param>
+    /// <returns>Returns the root of the subtree (from T1) by which T1 differs from T2, or null if no difference is found.</returns>
+    public static ISymbolicExpressionTreeNode Difference(this ISymbolicExpressionTree tree, ISymbolicExpressionTree other) {
+      return Difference(tree.Root, other.Root);
+    }
+
+    public static ISymbolicExpressionTreeNode Difference(this ISymbolicExpressionTreeNode node, ISymbolicExpressionTreeNode other) {
+      var a = node.IterateNodesPrefix().ToList();
+      var b = other.IterateNodesPrefix().ToList();
+      var list = new List<ISymbolicExpressionTreeNode>();
+      for (int i = 0, j = 0; i < a.Count && j < b.Count; ++i, ++j) {
+        var s1 = a[i].ToString();
+        var s2 = b[j].ToString();
+        if (s1 == s2) continue;
+        list.Add(a[i]);
+        // skip subtrees since the parents are already different
+        i += a[i].SubtreeCount;
+        j += b[j].SubtreeCount;
+      }
+      ISymbolicExpressionTreeNode result = list.Count > 0 ? LowestCommonAncestor(node, list) : null;
+      return result;
+    }
+
+    private static ISymbolicExpressionTreeNode LowestCommonAncestor(ISymbolicExpressionTreeNode root, List<ISymbolicExpressionTreeNode> nodes) {
+      if (nodes.Count == 0)
+        throw new ArgumentException("The nodes list should contain at least one element.");
+
+      if (nodes.Count == 1)
+        return nodes[0];
+
+      int minLevel = nodes.Min(x => root.GetBranchLevel(x));
+
+      // bring the nodes in the nodes to the same level (relative to the root)
+      for (int i = 0; i < nodes.Count; ++i) {
+        var node = nodes[i];
+        var level = root.GetBranchLevel(node);
+        for (int j = minLevel; j < level; ++j)
+          node = node.Parent;
+        nodes[i] = node;
+      }
+
+      // while not all the elements in the nodes are equal, go one level up
+      while (nodes.Any(x => x != nodes[0])) {
+        for (int i = 0; i < nodes.Count; ++i)
+          nodes[i] = nodes[i].Parent;
+      }
+
+      return nodes[0];
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator.cs	(revision 16337)
@@ -0,0 +1,107 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization.Operators;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [StorableClass]
+  [Item("SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator", "A similarity calculator based on the size of the maximum common subtree between two trees")]
+  public class SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator : SolutionSimilarityCalculator {
+    [Storable]
+    private readonly SymbolicExpressionTreeNodeEqualityComparer comparer;
+    public bool MatchVariableWeights {
+      get { return comparer.MatchVariableWeights; }
+      set { comparer.MatchVariableWeights = value; }
+    }
+
+    public bool MatchConstantValues {
+      get { return comparer.MatchConstantValues; }
+      set { comparer.MatchConstantValues = value; }
+    }
+
+    protected override bool IsCommutative { get { return true; } }
+
+    [StorableConstructor]
+    protected SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator(bool deserializing) : base(deserializing) { }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator(this, cloner);
+    }
+
+    protected SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator(SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator original, Cloner cloner)
+      : base(original, cloner) {
+      comparer = cloner.Clone(original.comparer);
+    }
+
+    public SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator() {
+      comparer = new SymbolicExpressionTreeNodeEqualityComparer {
+        MatchConstantValues = true,
+        MatchVariableNames = true,
+        MatchVariableWeights = true
+      };
+    }
+
+    public SymbolicExpressionTreeMaxCommonSubtreeSimilarityCalculator(bool matchVariableWeights, bool matchConstantValues) {
+      comparer = new SymbolicExpressionTreeNodeEqualityComparer {
+        MatchConstantValues = matchConstantValues,
+        MatchVariableNames = true,
+        MatchVariableWeights = matchVariableWeights
+      };
+    }
+
+    public double CalculateSimilarity(ISymbolicExpressionTree t1, ISymbolicExpressionTree t2) {
+      return MaxCommonSubtreeSimilarity(t1, t2, comparer);
+    }
+
+    public override double CalculateSolutionSimilarity(IScope leftSolution, IScope rightSolution) {
+      var t1 = leftSolution.Variables[SolutionVariableName].Value as ISymbolicExpressionTree;
+      var t2 = rightSolution.Variables[SolutionVariableName].Value as ISymbolicExpressionTree;
+
+      if (t1 == null || t2 == null)
+        throw new ArgumentException("Cannot calculate similarity when one of the arguments is null.");
+
+      return MaxCommonSubtreeSimilarity(t1, t2, comparer);
+    }
+
+    public static double MaxCommonSubtreeSimilarity(ISymbolicExpressionTree a, ISymbolicExpressionTree b, ISymbolicExpressionTreeNodeSimilarityComparer comparer) {
+      int max = 0;
+      var rootA = a.Root.GetSubtree(0).GetSubtree(0);
+      var rootB = b.Root.GetSubtree(0).GetSubtree(0);
+      foreach (var aa in rootA.IterateNodesBreadth()) {
+        int lenA = aa.GetLength();
+        if (lenA <= max) continue;
+        foreach (var bb in rootB.IterateNodesBreadth()) {
+          int lenB = bb.GetLength();
+          if (lenB <= max) continue;
+          int matches = SymbolicExpressionTreeMatching.Match(aa, bb, comparer);
+          if (max < matches)
+            max = matches;
+        }
+      }
+      return 2.0 * max / (rootA.GetLength() + rootB.GetLength());
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeNodeComparer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeNodeComparer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeNodeComparer.cs	(revision 16337)
@@ -0,0 +1,72 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  // this comparer considers that a < b if the type of a is "greater" than the type of b, for example:
+  // - A function node is "greater" than a terminal node
+  // - A variable terminal is "greater" than a constant terminal
+  // - used for bringing subtrees to a "canonical" form when the operation allows reordering of arguments
+  public class SymbolicExpressionTreeNodeComparer : ISymbolicExpressionTreeNodeComparer {
+    public static int CompareNodes(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      var ta = a as SymbolicExpressionTreeTerminalNode;
+      var tb = b as SymbolicExpressionTreeTerminalNode;
+
+      if (ta == null)
+        return tb == null ? String.CompareOrdinal(a.Symbol.Name, b.Symbol.Name) : -1;
+
+      if (tb == null)
+        return 1;
+
+      // at this point we know a and b are both terminals
+      var va = a as VariableTreeNode;
+      var vb = b as VariableTreeNode;
+
+      if (va != null)
+        return vb == null ? -1 : CompareVariables(va, vb);
+
+      if (vb != null)
+        return 1;
+
+      // at this point we know a and b are not variables
+      var ca = a as ConstantTreeNode;
+      var cb = b as ConstantTreeNode;
+
+      if (ca != null && cb != null)
+        return ca.Value.CompareTo(cb.Value);
+
+      // for other unknown terminal types, compare strings
+      return string.CompareOrdinal(a.ToString(), b.ToString());
+    }
+
+    private static int CompareVariables(VariableTreeNode a, VariableTreeNode b) {
+      int result = string.CompareOrdinal(a.VariableName, b.VariableName);
+      return result == 0 ? a.Weight.CompareTo(b.Weight) : result;
+    }
+
+    public int Compare(ISymbolicExpressionTreeNode x, ISymbolicExpressionTreeNode y) {
+      return CompareNodes(x, y);
+    }
+  }
+
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeNodeEqualityComparer.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeNodeEqualityComparer.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreeNodeEqualityComparer.cs	(revision 16337)
@@ -0,0 +1,97 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("SymbolicExpressionTreeNodeEqualityComparer", "An operator that checks node equality based on different similarity measures.")]
+  [StorableClass]
+  public class SymbolicExpressionTreeNodeEqualityComparer : Item, ISymbolicExpressionTreeNodeSimilarityComparer {
+    [StorableConstructor]
+    protected SymbolicExpressionTreeNodeEqualityComparer(bool deserializing) : base(deserializing) { }
+    protected SymbolicExpressionTreeNodeEqualityComparer(SymbolicExpressionTreeNodeEqualityComparer original, Cloner cloner)
+      : base(original, cloner) {
+      matchConstantValues = original.matchConstantValues;
+      matchVariableNames = original.matchVariableNames;
+      matchVariableWeights = original.matchVariableWeights;
+    }
+    public override IDeepCloneable Clone(Cloner cloner) { return new SymbolicExpressionTreeNodeEqualityComparer(this, cloner); }
+
+    // more flexible matching criteria 
+    [Storable]
+    private bool matchConstantValues;
+    public bool MatchConstantValues {
+      get { return matchConstantValues; }
+      set { matchConstantValues = value; }
+    }
+
+    [Storable]
+    private bool matchVariableNames;
+    public bool MatchVariableNames {
+      get { return matchVariableNames; }
+      set { matchVariableNames = value; }
+    }
+
+    [Storable]
+    private bool matchVariableWeights;
+    public bool MatchVariableWeights {
+      get { return matchVariableWeights; }
+      set { matchVariableWeights = value; }
+    }
+
+    [StorableHook(HookType.AfterDeserialization)]
+    private void AfterDeserialization() {
+    }
+
+    public SymbolicExpressionTreeNodeEqualityComparer() {
+      matchConstantValues = true;
+      matchVariableNames = true;
+      matchVariableWeights = true;
+    }
+
+    public int GetHashCode(ISymbolicExpressionTreeNode n) {
+      return n.ToString().ToLower().GetHashCode();
+    }
+
+    public bool Equals(ISymbolicExpressionTreeNode a, ISymbolicExpressionTreeNode b) {
+      if (!(a is SymbolicExpressionTreeTerminalNode))
+        // if a and b are non terminal nodes, check equality of symbol names
+        return !(b is SymbolicExpressionTreeTerminalNode) && a.Symbol.Name.Equals(b.Symbol.Name);
+      var va = a as VariableTreeNode;
+      if (va != null) {
+        var vb = b as VariableTreeNode;
+        if (vb == null) return false;
+
+        return (!MatchVariableNames || va.VariableName.Equals(vb.VariableName)) && (!MatchVariableWeights || va.Weight.Equals(vb.Weight));
+      }
+      var ca = a as ConstantTreeNode;
+      if (ca != null) {
+        var cb = b as ConstantTreeNode;
+        if (cb == null) return false;
+        return (!MatchConstantValues || ca.Value.Equals(cb.Value));
+      }
+      return false;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreePhenotypicSimilarityCalculator.cs
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreePhenotypicSimilarityCalculator.cs	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/TreeMatching/SymbolicExpressionTreePhenotypicSimilarityCalculator.cs	(revision 16337)
@@ -0,0 +1,101 @@
+﻿#region License Information
+/* HeuristicLab
+ * Copyright (C) 2002-2018 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
+ *
+ * This file is part of HeuristicLab.
+ *
+ * HeuristicLab is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * HeuristicLab is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
+ */
+#endregion
+
+using System;
+using HeuristicLab.Common;
+using HeuristicLab.Core;
+using HeuristicLab.Data;
+using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
+using HeuristicLab.Optimization.Operators;
+using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
+
+namespace HeuristicLab.Problems.DataAnalysis.Symbolic {
+  [Item("SymbolicExpressionTreePhenotypicSimilarityCalculator", "An operator that calculates the similarity betweeon two trees based on the correlation of their outputs.")]
+  [StorableClass]
+  public class SymbolicExpressionTreePhenotypicSimilarityCalculator : SolutionSimilarityCalculator {
+    [Storable]
+    public IDataAnalysisProblemData ProblemData { get; set; }
+    [Storable]
+    public ISymbolicDataAnalysisExpressionTreeInterpreter Interpreter { get; set; }
+
+    protected override bool IsCommutative { get { return true; } }
+
+    [StorableConstructor]
+    protected SymbolicExpressionTreePhenotypicSimilarityCalculator(bool deserializing) : base(deserializing) { }
+
+    public SymbolicExpressionTreePhenotypicSimilarityCalculator(SymbolicExpressionTreePhenotypicSimilarityCalculator original, Cloner cloner)
+      : base(original, cloner) {
+      this.ProblemData = cloner.Clone(original.ProblemData);
+      this.Interpreter = cloner.Clone(original.Interpreter);
+    }
+
+    public override IDeepCloneable Clone(Cloner cloner) {
+      return new SymbolicExpressionTreePhenotypicSimilarityCalculator(this, cloner);
+    }
+
+    public SymbolicExpressionTreePhenotypicSimilarityCalculator() { }
+
+    public double CalculateSimilarity(ISymbolicExpressionTree t1, ISymbolicExpressionTree t2) {
+      if (Interpreter == null || ProblemData == null)
+        throw new InvalidOperationException("Cannot calculate phenotypic similarity when no interpreter or problem data were set.");
+
+      var v1 = Interpreter.GetSymbolicExpressionTreeValues(t1, ProblemData.Dataset, ProblemData.TrainingIndices);
+      var v2 = Interpreter.GetSymbolicExpressionTreeValues(t2, ProblemData.Dataset, ProblemData.TrainingIndices);
+
+      if (v1.Variance().IsAlmost(0) && v2.Variance().IsAlmost(0))
+        return 1.0;
+
+      OnlineCalculatorError error;
+      var r = OnlinePearsonsRCalculator.Calculate(v1, v2, out error);
+
+      var r2 = error == OnlineCalculatorError.None ? r * r : 0;
+
+      if (r2 > 1.0)
+        r2 = 1.0;
+
+      return r2;
+    }
+
+    public override double CalculateSolutionSimilarity(IScope leftSolution, IScope rightSolution) {
+      if (leftSolution == rightSolution)
+        return 1.0;
+
+      if (!leftSolution.Variables.ContainsKey("EstimatedValues") || !rightSolution.Variables.ContainsKey("EstimatedValues"))
+        throw new ArgumentException("No estimated values are present in the subscopes.");
+
+      var leftValues = (DoubleArray)leftSolution.Variables["EstimatedValues"].Value;
+      var rightValues = (DoubleArray)rightSolution.Variables["EstimatedValues"].Value;
+
+      if (leftValues.Variance().IsAlmost(0) && rightValues.Variance().IsAlmost(0))
+        return 1.0;
+
+      OnlineCalculatorError error;
+      var r = OnlinePearsonsRCalculator.Calculate(leftValues, rightValues, out error);
+
+      var r2 = error == OnlineCalculatorError.None ? r * r : 0;
+
+      if (r2 > 1.0)
+        r2 = 1.0;
+
+      return r2;
+    }
+  }
+}
Index: /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/packages.config
===================================================================
--- /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/packages.config	(revision 16337)
+++ /branches/2968_infix_string_formatter/HeuristicLab.Problems.DataAnalysis.Symbolic/3.4/packages.config	(revision 16337)
@@ -0,0 +1,4 @@
+﻿<?xml version="1.0" encoding="utf-8"?>
+<packages>
+  <package id="System.Numerics.Vectors" version="4.5.0" targetFramework="net45" />
+</packages>
