source: trunk/sources/HeuristicLab.GP/Recombination/UniformCrossover.cs @ 814

#region License Information
/* HeuristicLab
 * Copyright (C) 2002-2008 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.Core;
using HeuristicLab.Operators;
using HeuristicLab.Random;
using HeuristicLab.Data;
using HeuristicLab.Constraints;
using System.Diagnostics;

namespace HeuristicLab.GP {
  /// <summary>
  /// Implementation of a homologous uniform crossover operator as described in: 
  /// R. Poli and W. B. Langdon.  On the Search Properties of Different Crossover Operators in Genetic Programming.
  /// In Proceedings of Genetic Programming '98, Madison, Wisconsin, 1998.
  /// </summary>
  public class UniformCrossover : OperatorBase {
    public override string Description {
      get {
        return @"Uniform crossover as defined by Poli and Langdon";
      }
    }
    public UniformCrossover()
      : base() {
      AddVariableInfo(new VariableInfo("Random", "Pseudo random number generator", typeof(MersenneTwister), VariableKind.In));
      AddVariableInfo(new VariableInfo("OperatorLibrary", "The operator library containing all available operators", typeof(GPOperatorLibrary), VariableKind.In));
      AddVariableInfo(new VariableInfo("FunctionTree", "The tree to mutate", typeof(IFunctionTree), VariableKind.In | VariableKind.New));
      AddVariableInfo(new VariableInfo("TreeSize", "The size (number of nodes) of the tree", typeof(IntData), VariableKind.In | VariableKind.New));
      AddVariableInfo(new VariableInfo("TreeHeight", "The height of the tree", typeof(IntData), VariableKind.In | VariableKind.New));
    }

    public override IOperation Apply(IScope scope) {
      MersenneTwister random = GetVariableValue<MersenneTwister>("Random", scope, true);
      GPOperatorLibrary opLibrary = GetVariableValue<GPOperatorLibrary>("OperatorLibrary", scope, true);
      TreeGardener gardener = new TreeGardener(random, opLibrary);

      if ((scope.SubScopes.Count % 2) != 0)
        throw new InvalidOperationException("Number of parents is not even");

      CompositeOperation initOperations = new CompositeOperation();

      int crossoverEvents = scope.SubScopes.Count / 2;
      for (int i = 0; i < crossoverEvents; i++) {
        IScope parent1 = scope.SubScopes[0];
        scope.RemoveSubScope(parent1);
        IScope parent2 = scope.SubScopes[0];
        scope.RemoveSubScope(parent2);
        IScope child0 = new Scope((i * 2).ToString());
        IScope child1 = new Scope((i * 2 + 1).ToString());
        Cross(scope, random, gardener, parent1, parent2, child0, child1);
        scope.AddSubScope(child0);
        scope.AddSubScope(child1);
      }

      return null;
    }

    private void Cross(IScope scope, MersenneTwister random, TreeGardener gardener, IScope parent1, IScope parent2, IScope child0, IScope child1) {
      IFunctionTree childTree0;
      IFunctionTree childTree1;
      Cross(random, gardener, parent1, parent2, out childTree0, out childTree1);
      Debug.Assert(gardener.IsValidTree(childTree0));
      Debug.Assert(gardener.IsValidTree(childTree1));
      child0.AddVariable(new HeuristicLab.Core.Variable(scope.TranslateName("FunctionTree"), childTree0));
      child0.AddVariable(new HeuristicLab.Core.Variable(scope.TranslateName("TreeSize"), new IntData(childTree0.Size)));
      child0.AddVariable(new HeuristicLab.Core.Variable(scope.TranslateName("TreeHeight"), new IntData(childTree0.Height)));

      child1.AddVariable(new HeuristicLab.Core.Variable(scope.TranslateName("FunctionTree"), childTree1));
      child1.AddVariable(new HeuristicLab.Core.Variable(scope.TranslateName("TreeSize"), new IntData(childTree1.Size)));
      child1.AddVariable(new HeuristicLab.Core.Variable(scope.TranslateName("TreeHeight"), new IntData(childTree1.Height)));
    }


    private void Cross(MersenneTwister random, TreeGardener gardener, IScope f, IScope g, out IFunctionTree child0, out IFunctionTree child1) {
      IFunctionTree tree0 = f.GetVariableValue<IFunctionTree>("FunctionTree", false);
      int tree0Height = f.GetVariableValue<IntData>("TreeHeight", false).Data;
      int tree0Size = f.GetVariableValue<IntData>("TreeSize", false).Data;

      IFunctionTree tree1 = g.GetVariableValue<IFunctionTree>("FunctionTree", false);
      int tree1Height = g.GetVariableValue<IntData>("TreeHeight", false).Data;
      int tree1Size = g.GetVariableValue<IntData>("TreeSize", false).Data;

      List<CrossoverPoint> allowedCrossOverPoints = GetCrossOverPoints(gardener, tree0, tree1);
      foreach (CrossoverPoint p in allowedCrossOverPoints) {
        Debug.Assert(gardener.GetAllowedSubFunctions(p.parent0.Function, p.childIndex).Contains(p.parent1.SubTrees[p.childIndex].Function));
        Debug.Assert(gardener.GetAllowedSubFunctions(p.parent1.Function, p.childIndex).Contains(p.parent0.SubTrees[p.childIndex].Function));
      }
      // iterate through the list of crossover points and swap nodes with p=0.5
      foreach (CrossoverPoint crossoverPoint in allowedCrossOverPoints) {
        if (random.NextDouble() < 0.5) {
          IFunctionTree parent0 = crossoverPoint.parent0;
          IFunctionTree parent1 = crossoverPoint.parent1;
          IFunctionTree branch0 = crossoverPoint.parent0.SubTrees[crossoverPoint.childIndex];
          IFunctionTree branch1 = crossoverPoint.parent1.SubTrees[crossoverPoint.childIndex];

          // if we are at an internal node of the common region swap only the node but not the subtrees
          if (branch0.SubTrees.Count == branch1.SubTrees.Count) {
            if (parent0 != null) {
              Debug.Assert(parent1 != null); Debug.Assert(branch0 != null); Debug.Assert(branch0 != null);
              Debug.Assert(gardener.GetAllowedSubFunctions(parent0.Function, crossoverPoint.childIndex).Contains(branch1.Function));
              Debug.Assert(gardener.GetAllowedSubFunctions(parent1.Function, crossoverPoint.childIndex).Contains(branch0.Function));
              // we are not at the root => exchange the branches in the parent
              parent0.RemoveSubTree(crossoverPoint.childIndex);
              parent1.RemoveSubTree(crossoverPoint.childIndex);
              parent0.InsertSubTree(crossoverPoint.childIndex, branch1);
              parent1.InsertSubTree(crossoverPoint.childIndex, branch0);
            }
            // always exchange all children
            List<IFunctionTree> branch0Children = new List<IFunctionTree>(branch0.SubTrees); // create backup lists
            List<IFunctionTree> branch1Children = new List<IFunctionTree>(branch1.SubTrees);
            while (branch0.SubTrees.Count > 0) branch0.RemoveSubTree(0); // remove all children
            while (branch1.SubTrees.Count > 0) branch1.RemoveSubTree(0);
            foreach (IFunctionTree subTree in branch1Children) {
              Debug.Assert(gardener.GetAllowedSubFunctions(branch0.Function, branch0.SubTrees.Count).Contains(subTree.Function));
              branch0.AddSubTree(subTree); // append children of branch1 to branch0
            }
            foreach (IFunctionTree subTree in branch0Children) {
              Debug.Assert(gardener.GetAllowedSubFunctions(branch1.Function, branch1.SubTrees.Count).Contains(subTree.Function));
              branch1.AddSubTree(subTree); // and vice versa
            }
          } else {
            // If we are at a node at the border of the common region then exchange the whole branch.
            // If we are at the root node and the number of children is already different we can't do anything now but
            // at the end either tree0 or tree1 must be returned with p=0.5.

            // However if we are not at the root => exchange the branches in the parent
            if (parent0 != null) {
              Debug.Assert(parent1 != null); Debug.Assert(branch0 != null); Debug.Assert(branch1 != null);
              Debug.Assert(gardener.GetAllowedSubFunctions(parent0.Function, crossoverPoint.childIndex).Contains(branch1.Function));
              Debug.Assert(gardener.GetAllowedSubFunctions(parent1.Function, crossoverPoint.childIndex).Contains(branch0.Function));
              parent0.RemoveSubTree(crossoverPoint.childIndex);
              parent1.RemoveSubTree(crossoverPoint.childIndex);
              parent0.InsertSubTree(crossoverPoint.childIndex, branch1);
              parent1.InsertSubTree(crossoverPoint.childIndex, branch0);
            }
          }
        }
      }
      child0 = tree0;
      child1 = tree1;
    }

    class CrossoverPoint {
      public IFunctionTree parent0;
      public IFunctionTree parent1;
      public int childIndex;
    }

    private List<CrossoverPoint> GetCrossOverPoints(TreeGardener gardener, IFunctionTree branch0, IFunctionTree branch1) {
      List<CrossoverPoint> results = new List<CrossoverPoint>();
      if (branch0.SubTrees.Count != branch1.SubTrees.Count) return results;

      for (int i = 0; i < branch0.SubTrees.Count; i++) {
        // if the branches fit to the parent
        if (gardener.GetAllowedSubFunctions(branch0.Function, i).Contains(branch1.SubTrees[i].Function) &&
          gardener.GetAllowedSubFunctions(branch1.Function, i).Contains(branch0.SubTrees[i].Function)) {
          // if the point is at the border of the common region we don't care about the children
          // however if the point is not on the border of the common region we also have to check if
          // the children of the branches fit together
          bool fit = true;
          if (branch0.SubTrees[i].SubTrees.Count == branch1.SubTrees[i].SubTrees.Count) {
            for (int j = 0; j < branch0.SubTrees[i].SubTrees.Count; j++) {
              fit = fit & gardener.GetAllowedSubFunctions(branch0.SubTrees[i].Function, j).Contains(branch1.SubTrees[i].SubTrees[j].Function);
              fit = fit & gardener.GetAllowedSubFunctions(branch1.SubTrees[i].Function, j).Contains(branch0.SubTrees[i].SubTrees[j].Function);
            }
          }
          if (fit) {
            CrossoverPoint p = new CrossoverPoint();
            p.childIndex = i;
            p.parent0 = branch0;
            p.parent1 = branch1;
            results.Add(p);
          }
        }
        results.AddRange(GetCrossOverPoints(gardener, branch0.SubTrees[i], branch1.SubTrees[i]));
      }
      return results;
    }
  }
}