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source: trunk/sources/HeuristicLab.GP.Operators/3.3/Manipulation/DeleteSubTreeManipulation.cs @ 2482

Last change on this file since 2482 was 2222, checked in by gkronber, 15 years ago

Merged changes from GP-refactoring branch back into the trunk #713.

File size: 4.1 KB
Line 
1#region License Information
2/* HeuristicLab
3 * Copyright (C) 2002-2008 Heuristic and Evolutionary Algorithms Laboratory (HEAL)
4 *
5 * This file is part of HeuristicLab.
6 *
7 * HeuristicLab is free software: you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation, either version 3 of the License, or
10 * (at your option) any later version.
11 *
12 * HeuristicLab is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with HeuristicLab. If not, see <http://www.gnu.org/licenses/>.
19 */
20#endregion
21
22using System.Collections.Generic;
23using HeuristicLab.Core;
24using HeuristicLab.Random;
25using System.Diagnostics;
26using HeuristicLab.GP.Interfaces;
27
28namespace HeuristicLab.GP.Operators {
29  public class DeleteSubTreeManipulation : GPManipulatorBase {
30    public override string Description {
31      get {
32        return @"Deletes a random sub-tree of the input tree. If the remaining tree is not valid
33the operator tries to fix the tree by generating random subtrees where necessary.";
34      }
35    }
36
37    public DeleteSubTreeManipulation()
38      : base() {
39    }
40
41    internal override IOperation Manipulate(MersenneTwister random, IGeneticProgrammingModel gpModel, FunctionLibrary library, int maxTreeSize, int maxTreeHeight, IScope scope) {
42      TreeGardener gardener = new TreeGardener(random, library);
43      IFunctionTree parent = gardener.GetRandomParentNode(gpModel.FunctionTree);
44
45      // parent==null means the whole tree should be deleted.
46      // => return a new minimal random tree
47      if (parent == null) {
48        IFunctionTree newTree = gardener.CreateBalancedRandomTree(1, 1);
49        // check if the tree is ok
50        Debug.Assert(gardener.IsValidTree(newTree));
51        gpModel.FunctionTree = newTree;
52        // schedule an operation to initialize the newly created operator
53        return Util.CreateInitializationOperation(TreeGardener.GetAllSubTrees(newTree), scope);
54      }
55
56      // select a branch to prune
57      int childIndex = random.Next(parent.SubTrees.Count);
58      if (parent.SubTrees.Count > parent.Function.MinSubTrees) {
59        parent.RemoveSubTree(childIndex);
60        // actually since the next sub-trees are shifted in the place of the removed branch
61        // it might be possible that these sub-trees are not allowed in the place of the old branch
62        // we ignore this problem for now.
63        // when this starts to become a problem a possible solution is to go through the shifted branches from the place of the shifted
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)
65
66        Debug.Assert(gardener.IsValidTree(gpModel.FunctionTree));
67        // recalculate size and height
68        gpModel.Size = gpModel.FunctionTree.GetSize();
69        gpModel.Height = gpModel.FunctionTree.GetHeight();
70        // root hasn't changed so don't need to update 'FunctionTree' variable
71        return null;
72      } else {
73        // replace with a minimal random seedling
74        parent.RemoveSubTree(childIndex);
75        ICollection<IFunction> allowedFunctions = gardener.GetAllowedSubFunctions(parent.Function, childIndex);
76        IFunctionTree newFunctionTree = gardener.CreateRandomTree(allowedFunctions, 1, 1);
77        parent.InsertSubTree(childIndex, newFunctionTree);
78        Debug.Assert(gardener.IsValidTree(gpModel.FunctionTree));
79        // recalculate size and height
80        gpModel.Size = gpModel.FunctionTree.GetSize();
81        gpModel.Height = gpModel.FunctionTree.GetHeight();
82        // return an initialization operation for the newly created tree
83        return Util.CreateInitializationOperation(TreeGardener.GetAllSubTrees(newFunctionTree), scope);
84      }
85    }
86  }
87}
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