source: branches/HeuristicLab.EvolutionaryTracking/HeuristicLab.Encodings.SymbolicExpressionTreeEncoding/3.4/Crossovers/TracingSymbolicExpressionTreeCrossover.cs @ 7792

#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.Collections.Generic;
using System.Linq;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HeuristicLab.Data;
using HeuristicLab.Parameters;
using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;

using CloneMapType = HeuristicLab.Core.ItemDictionary<HeuristicLab.Core.IItem, HeuristicLab.Core.IItem>;
using TraceMapType = HeuristicLab.Core.ItemDictionary<HeuristicLab.Core.IItem, HeuristicLab.Core.IItemList<HeuristicLab.Core.IItem>>;

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 : SymbolicExpressionTreeOperator, ISymbolicExpressionTreeCrossover {
    private const string ParentsParameterName = "Parents";
    private const string ChildParameterName = "Child";
    private const string GlobalTraceMapParameterName = "GlobalTraceMap";
    private const string GlobalCloneMapParameterName = "GlobalCloneMap";
    private const string GlobalFragmentMapParameterName = "GlobalFragmentMap";

    #region Parameter Properties
    public ILookupParameter<ItemArray<ISymbolicExpressionTree>> ParentsParameter {
      get { return (ScopeTreeLookupParameter<ISymbolicExpressionTree>)Parameters[ParentsParameterName]; }
    }
    public ILookupParameter<ISymbolicExpressionTree> ChildParameter {
      get { return (ILookupParameter<ISymbolicExpressionTree>)Parameters[ChildParameterName]; }
    }
    public LookupParameter<CloneMapType> GlobalCloneMapParameter {
      get { return (LookupParameter<CloneMapType>)Parameters[GlobalCloneMapParameterName]; }
    }
    public LookupParameter<TraceMapType> GlobalTraceMapParameter {
      get { return (LookupParameter<TraceMapType>)Parameters[GlobalTraceMapParameterName]; }
    }
    public LookupParameter<CloneMapType> GlobalFragmentMapParameter {
      get { return (LookupParameter<CloneMapType>)Parameters[GlobalFragmentMapParameterName]; }
    }
    #endregion

    #region Properties
    public ItemArray<ISymbolicExpressionTree> Parents {
      get { return ParentsParameter.ActualValue; }
    }
    public ISymbolicExpressionTree Child {
      get { return ChildParameter.ActualValue; }
      set { ChildParameter.ActualValue = value; }
    }
    public CloneMapType GlobalCloneMap {
      get { return GlobalCloneMapParameter.ActualValue; }
    }
    public TraceMapType GlobalTraceMap {
      get { return GlobalTraceMapParameter.ActualValue; }
    }
    public CloneMapType GlobalFragmentMap {
      get { return GlobalFragmentMapParameter.ActualValue; }
    }
    #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."));
      Parameters.Add(new LookupParameter<CloneMapType>(GlobalCloneMapParameterName, "A global map keeping track of trees and their clones (made during selection)."));
      Parameters.Add(new LookupParameter<CloneMapType>(GlobalFragmentMapParameterName, "A global map keeping track of tree fragments received via crossover."));
      Parameters.Add(new LookupParameter<TraceMapType>(GlobalTraceMapParameterName, "A global cache containing tracing info."));
    }

    public sealed override IOperation Apply() {
      if (Parents.Length != 2)
        throw new ArgumentException("Number of parents must be exactly two for symbolic expression tree crossover operators.");

      // add global trace cache if not already present in global scope
      var gScope = ExecutionContext.Scope;
      while (gScope.Parent != null)
        gScope = gScope.Parent;
      if (GlobalTraceMap == null)
        gScope.Variables.Add(new Variable(GlobalTraceMapParameterName, new TraceMapType()));
      if (GlobalFragmentMap == null)
        gScope.Variables.Add(new Variable(GlobalFragmentMapParameterName, new CloneMapType()));

      // get original parents (this info will be needed later to construct the genealogy graph)
      var originalParents = new ItemList<IItem>(Parents.Select(x => GlobalCloneMap[x]));

      // save the nodes of parent0 in a list so we can track what modifications are made by crossover
      var nodes0 = Parents[0].IterateNodesBreadth() as List<ISymbolicExpressionTreeNode>;

      //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 nodes1 = Child.IterateNodesBreadth() as List<ISymbolicExpressionTreeNode>;

      // compare the two nodes lists and check the difference (comparing node references so we avoid false functional identity). 
      // if no difference is found, then it is assumed that the whole tree was swapped with itself (it can happen), so the index is 0
      int i, min = Math.Max(nodes0.Count, nodes1.Count);
      for (i = 0; i != min; ++i)
        if (nodes0[i] != nodes1[i]) break;
      if (i == min) i = 0;

      // add heredity information into the global variables
      GlobalTraceMap[Child] = originalParents; // map child to its corresponding parents from the previous generation
      GlobalFragmentMap[Child] = new IntValue(i); // map child to the index of its fragment
      return base.Apply();
    }

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