1 | #region License Information
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2 | /* HeuristicLab
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3 | * Copyright (C) 2002-2008 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
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4 | *
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5 | * This file is part of HeuristicLab.
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6 | *
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7 | * HeuristicLab is free software: you can redistribute it and/or modify
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8 | * it under the terms of the GNU General Public License as published by
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9 | * the Free Software Foundation, either version 3 of the License, or
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10 | * (at your option) any later version.
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11 | *
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12 | * HeuristicLab is distributed in the hope that it will be useful,
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13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
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14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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15 | * GNU General Public License for more details.
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16 | *
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17 | * You should have received a copy of the GNU General Public License
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18 | * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
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19 | */
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20 | #endregion
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21 |
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22 | using System.Collections.Generic;
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23 | using HeuristicLab.Core;
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24 | using HeuristicLab.Random;
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25 | using System.Diagnostics;
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26 | using HeuristicLab.GP.Interfaces;
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27 |
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28 | namespace HeuristicLab.GP.Operators {
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29 | public class DeleteSubTreeManipulation : GPManipulatorBase {
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30 | public override string Description {
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31 | get {
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32 | return @"Deletes a random sub-tree of the input tree. If the remaining tree is not valid
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33 | the operator tries to fix the tree by generating random subtrees where necessary.";
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34 | }
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35 | }
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36 |
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37 | public DeleteSubTreeManipulation()
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38 | : base() {
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39 | }
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40 |
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41 | internal override IOperation Manipulate(MersenneTwister random, IGeneticProgrammingModel gpModel, FunctionLibrary library, int maxTreeSize, int maxTreeHeight, IScope scope) {
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42 | TreeGardener gardener = new TreeGardener(random, library);
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43 | IFunctionTree parent = gardener.GetRandomParentNode(gpModel.FunctionTree);
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44 |
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45 | // parent==null means the whole tree should be deleted.
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46 | // => return a new minimal random tree
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47 | if (parent == null) {
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48 | IFunctionTree newTree = gardener.CreateBalancedRandomTree(1, 1);
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49 | // check if the tree is ok
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50 | Debug.Assert(gardener.IsValidTree(newTree));
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51 | gpModel.FunctionTree = newTree;
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52 | // schedule an operation to initialize the newly created operator
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53 | return Util.CreateInitializationOperation(TreeGardener.GetAllSubTrees(newTree), scope);
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54 | }
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55 |
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56 | // select a branch to prune
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57 | int childIndex = random.Next(parent.SubTrees.Count);
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58 | if (parent.SubTrees.Count > parent.Function.MinSubTrees) {
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59 | parent.RemoveSubTree(childIndex);
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60 | // actually since the next sub-trees are shifted in the place of the removed branch
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61 | // it might be possible that these sub-trees are not allowed in the place of the old branch
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62 | // we ignore this problem for now.
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63 | // when this starts to become a problem a possible solution is to go through the shifted branches from the place of the shifted
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64 | // and find the first one that doesn't fit. At this position we insert a new randomly initialized subtree of matching type (gkronber 25.12.07)
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65 |
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66 | Debug.Assert(gardener.IsValidTree(gpModel.FunctionTree));
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67 | // root hasn't changed so don't need to update 'FunctionTree' variable
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68 | return null;
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69 | } else {
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70 | // replace with a minimal random seedling
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71 | parent.RemoveSubTree(childIndex);
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72 | ICollection<IFunction> allowedFunctions = gardener.GetAllowedSubFunctions(parent.Function, childIndex);
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73 | IFunctionTree newFunctionTree = gardener.CreateRandomTree(allowedFunctions, 1, 1);
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74 | parent.InsertSubTree(childIndex, newFunctionTree);
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75 | Debug.Assert(gardener.IsValidTree(gpModel.FunctionTree));
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76 | // return an initialization operation for the newly created tree
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77 | return Util.CreateInitializationOperation(TreeGardener.GetAllSubTrees(newFunctionTree), scope);
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78 | }
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79 | }
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80 | }
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81 | }
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