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source: branches/HeuristicLab.EvolutionaryTracking/HeuristicLab.Encodings.SymbolicExpressionTreeEncoding/3.4/Manipulators/RemoveBranchManipulation.cs @ 13187

Last change on this file since 13187 was 9834, checked in by bburlacu, 11 years ago

#1772: Manually merged HeuristicLab.Encodings.SymbolicExpressionTreeEncoding project from the trunk to the branch.

File size: 6.7 KB
Line 
1#region License Information
2/* HeuristicLab
3 * Copyright (C) 2002-2013 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 System.Linq;
24using HeuristicLab.Common;
25using HeuristicLab.Core;
26using HeuristicLab.Data;
27using HeuristicLab.Parameters;
28using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
29
30namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
31  [StorableClass]
32  [Item("RemoveBranchManipulation", "Removes a random sub-tree of the input tree and fixes the tree by generating random subtrees if necessary..")]
33  public sealed class RemoveBranchManipulation : TracingSymbolicExpressionTreeManipulator, ISymbolicExpressionTreeSizeConstraintOperator {
34    private const int MAX_TRIES = 100;
35    private const string MaximumSymbolicExpressionTreeLengthParameterName = "MaximumSymbolicExpressionTreeLength";
36    private const string MaximumSymbolicExpressionTreeDepthParameterName = "MaximumSymbolicExpressionTreeDepth";
37    #region Parameter Properties
38    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeLengthParameter {
39      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeLengthParameterName]; }
40    }
41    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeDepthParameter {
42      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeDepthParameterName]; }
43    }
44    #endregion
45    #region Properties
46    public IntValue MaximumSymbolicExpressionTreeLength {
47      get { return MaximumSymbolicExpressionTreeLengthParameter.ActualValue; }
48    }
49    public IntValue MaximumSymbolicExpressionTreeDepth {
50      get { return MaximumSymbolicExpressionTreeDepthParameter.ActualValue; }
51    }
52    #endregion
53
54    [StorableConstructor]
55    private RemoveBranchManipulation(bool deserializing) : base(deserializing) { }
56    private RemoveBranchManipulation(RemoveBranchManipulation original, Cloner cloner) : base(original, cloner) { }
57    public RemoveBranchManipulation()
58      : base() {
59      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeLengthParameterName, "The maximal length (number of nodes) of the symbolic expression tree."));
60      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeDepthParameterName, "The maximal depth of the symbolic expression tree (a tree with one node has depth = 0)."));
61    }
62
63    public override IDeepCloneable Clone(Cloner cloner) {
64      return new RemoveBranchManipulation(this, cloner);
65    }
66
67    protected override void Manipulate(IRandom random, ISymbolicExpressionTree symbolicExpressionTree) {
68      RemoveRandomBranch(random, symbolicExpressionTree, MaximumSymbolicExpressionTreeLength.Value, MaximumSymbolicExpressionTreeDepth.Value);
69    }
70
71    public static void RemoveRandomBranch(IRandom random, ISymbolicExpressionTree symbolicExpressionTree, int maxTreeLength, int maxTreeDepth) {
72      var allowedSymbols = new List<ISymbol>();
73      ISymbolicExpressionTreeNode parent;
74      int childIndex;
75      int maxLength;
76      int maxDepth;
77      // repeat until a fitting parent and child are found (MAX_TRIES times)
78      int tries = 0;
79
80      var nodes = symbolicExpressionTree.Root.IterateNodesPrefix().Skip(1).Where(n => n.SubtreeCount > 0).ToList();
81      do {
82        parent = nodes.SelectRandom(random);
83        childIndex = random.Next(parent.SubtreeCount);
84        var child = parent.GetSubtree(childIndex);
85        maxLength = maxTreeLength - symbolicExpressionTree.Length + child.GetLength();
86        maxDepth = maxTreeDepth - symbolicExpressionTree.Depth + child.GetDepth();
87
88        allowedSymbols.Clear();
89        foreach (var symbol in parent.Grammar.GetAllowedChildSymbols(parent.Symbol, childIndex)) {
90          // check basic properties that the new symbol must have
91          if (symbol.Name != child.Symbol.Name &&
92            symbol.InitialFrequency > 0 &&
93            parent.Grammar.GetMinimumExpressionDepth(symbol) + 1 <= maxDepth &&
94            parent.Grammar.GetMinimumExpressionLength(symbol) <= maxLength) {
95            allowedSymbols.Add(symbol);
96          }
97        }
98        tries++;
99      } while (tries < MAX_TRIES && allowedSymbols.Count == 0);
100
101      if (tries >= MAX_TRIES) return;
102      ReplaceWithMinimalTree(random, symbolicExpressionTree.Root, parent, childIndex);
103    }
104
105    private static void ReplaceWithMinimalTree(IRandom random, ISymbolicExpressionTreeNode root, ISymbolicExpressionTreeNode parent, int childIndex) {
106      // determine possible symbols that will lead to the smallest possible tree
107      var possibleSymbols = (from s in parent.Grammar.GetAllowedChildSymbols(parent.Symbol, childIndex)
108                             where s.InitialFrequency > 0.0
109                             group s by parent.Grammar.GetMinimumExpressionLength(s) into g
110                             orderby g.Key
111                             select g).First().ToList();
112      var weights = possibleSymbols.Select(x => x.InitialFrequency).ToList();
113      var selectedSymbol = possibleSymbols.SelectRandom(weights, random);
114      var newTreeNode = selectedSymbol.CreateTreeNode();
115      if (newTreeNode.HasLocalParameters) newTreeNode.ResetLocalParameters(random);
116      parent.RemoveSubtree(childIndex);
117      parent.InsertSubtree(childIndex, newTreeNode);
118
119      var topLevelNode = newTreeNode as SymbolicExpressionTreeTopLevelNode;
120      if (topLevelNode != null)
121        topLevelNode.SetGrammar((ISymbolicExpressionTreeGrammar)root.Grammar.Clone());
122
123      for (int i = 0; i < newTreeNode.Grammar.GetMinimumSubtreeCount(newTreeNode.Symbol); i++) {
124        // insert a dummy sub-tree and add the pending extension to the list
125        var dummy = new SymbolicExpressionTreeNode();
126        newTreeNode.AddSubtree(dummy);
127        // replace the just inserted dummy by recursive application
128        ReplaceWithMinimalTree(random, root, newTreeNode, i);
129      }
130    }
131  }
132}
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