source: branches/HeuristicLab.EvolutionaryTracking/HeuristicLab.Encodings.SymbolicExpressionTreeEncoding/3.4/Crossovers/TracingSymbolicExpressionTreeCrossover.cs @ 12547

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2012 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.Parameters;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;

namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
  /// <summary>
  /// A base class for operators that perform a crossover of symbolic expression trees.
  /// </summary>
  [Item("SymbolicExpressionTreeCrossover", "A base class for operators that perform a crossover of symbolic expression trees.")]
  [StorableClass]
  public abstract class TracingSymbolicExpressionTreeCrossover : TracingSymbolicExpressionTreeOperator, ISymbolicExpressionTreeCrossover {
    private const string ParentsParameterName = "Parents";
    private const string ChildParameterName = "Child";

    #region Parameter Properties
    public ILookupParameter<ItemArray<ISymbolicExpressionTree>> ParentsParameter {
      get { return (ScopeTreeLookupParameter<ISymbolicExpressionTree>)Parameters[ParentsParameterName]; }
    }
    public ILookupParameter<ISymbolicExpressionTree> ChildParameter {
      get { return (ILookupParameter<ISymbolicExpressionTree>)Parameters[ChildParameterName]; }
    }
    #endregion

    #region Properties
    public ItemArray<ISymbolicExpressionTree> Parents {
      get { return ParentsParameter.ActualValue; }
    }
    public ISymbolicExpressionTree Child {
      get { return ChildParameter.ActualValue; }
      set { ChildParameter.ActualValue = value; }
    }
    #endregion

    [StorableConstructor]
    protected TracingSymbolicExpressionTreeCrossover(bool deserializing)
      : base(deserializing) {
    }
    protected TracingSymbolicExpressionTreeCrossover(TracingSymbolicExpressionTreeCrossover original, Cloner cloner)
      : base(original, cloner) {
    }
    protected TracingSymbolicExpressionTreeCrossover()
      : base() {
      Parameters.Add(new ScopeTreeLookupParameter<ISymbolicExpressionTree>(ParentsParameterName, "The parent symbolic expression trees which should be crossed."));
      Parameters.Add(new LookupParameter<ISymbolicExpressionTree>(ChildParameterName, "The child symbolic expression tree resulting from the crossover."));
    }
    public override IOperation Apply() {
      if (Parents.Length != 2)
        throw new ArgumentException("Number of parents must be exactly two for symbolic expression tree crossover operators.");

      AddTracingVariablesToGlobalScope();

      // save the nodes of parent0 in a list so we can track what modifications are made by crossover
      var nodes0 = Parents[0].IterateNodesPrefix().ToList();
      var nodes1 = Parents[1].IterateNodesPrefix().ToList();

      // perform crossover
      Child = Crossover(Random, Parents[0], Parents[1]);

      // create another list of parent0's nodes, so we can compare it with the first list to see what changed
      var childNodes = Child.IterateNodesPrefix().ToList();

      // compare the two node lists and check the difference (comparing node references so we avoid false functional identity). 
      int i = 0, min0 = Math.Min(nodes0.Count, childNodes.Count);
      // find the index of the fragment (with respect to the prefix order of nodes) in Parent0
      while (i < min0 && ReferenceEquals(nodes0[i], childNodes[i])) ++i;

      var fragmentRoot = (i == min0) ? null : childNodes[i];
      int j = 0;
      // find the index of the fragment (with respect to the prefix order of nodes) in Parent1
      while (j < nodes1.Count && !ReferenceEquals(nodes1[j], fragmentRoot)) ++j; // this works because the swapped subtree is not removed from the non-root parent

      if (i < min0 && j < nodes1.Count && !ReferenceEquals(childNodes[i], nodes1[j])) {
        throw new Exception("The two array elements should reference the same subtree.");
      }

      // map child to its corresponding parents from the previous generation
      GlobalTraceMap[Child] = new ItemList<IItem>(from p in Parents select GlobalCloneMap[p]);
      var fragment0 = new Fragment { Root = i == min0 ? null : nodes0[i], Index = i }; // fragment replaced in Parent0
      var fragment1 = new Fragment { Root = fragmentRoot, Index = i, OldIndex = j }; // fragment received from Parent1
      GlobalFragmentMap[Child] = fragment1; // map child to the index of its fragment
      // transaction.FragmentIn = the fragment received from the other parent
      // transaction.FragmentOut = the fragment that got replaced
      GlobalGeneticExchangeMap.Add(new GeneticExchange { FragmentIn = fragment1, FragmentOut = fragment0 });
      return base.Apply();
    }

    public abstract ISymbolicExpressionTree Crossover(IRandom random, ISymbolicExpressionTree parent0, ISymbolicExpressionTree parent1);
  }
}