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source: trunk/HeuristicLab.Encodings.SymbolicExpressionTreeEncoding/3.4/Manipulators/RemoveBranchManipulation.cs @ 16752

Last change on this file since 16752 was 16565, checked in by gkronber, 6 years ago

#2520: merged changes from PersistenceOverhaul branch (r16451:16564) into trunk

File size: 6.7 KB
Line 
1#region License Information
2/* HeuristicLab
3 * Copyright (C) 2002-2019 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 HEAL.Attic;
29using HeuristicLab.Random;
30
31namespace HeuristicLab.Encodings.SymbolicExpressionTreeEncoding {
32  [StorableType("639F837E-3AF9-4783-9AC2-0A4DC8991FED")]
33  [Item("RemoveBranchManipulation", "Removes a random sub-tree of the input tree and fixes the tree by generating random subtrees if necessary..")]
34  public sealed class RemoveBranchManipulation : SymbolicExpressionTreeManipulator, ISymbolicExpressionTreeSizeConstraintOperator {
35    private const int MAX_TRIES = 100;
36    private const string MaximumSymbolicExpressionTreeLengthParameterName = "MaximumSymbolicExpressionTreeLength";
37    private const string MaximumSymbolicExpressionTreeDepthParameterName = "MaximumSymbolicExpressionTreeDepth";
38    #region Parameter Properties
39    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeLengthParameter {
40      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeLengthParameterName]; }
41    }
42    public IValueLookupParameter<IntValue> MaximumSymbolicExpressionTreeDepthParameter {
43      get { return (IValueLookupParameter<IntValue>)Parameters[MaximumSymbolicExpressionTreeDepthParameterName]; }
44    }
45    #endregion
46    #region Properties
47    public IntValue MaximumSymbolicExpressionTreeLength {
48      get { return MaximumSymbolicExpressionTreeLengthParameter.ActualValue; }
49    }
50    public IntValue MaximumSymbolicExpressionTreeDepth {
51      get { return MaximumSymbolicExpressionTreeDepthParameter.ActualValue; }
52    }
53    #endregion
54
55    [StorableConstructor]
56    private RemoveBranchManipulation(StorableConstructorFlag _) : base(_) { }
57    private RemoveBranchManipulation(RemoveBranchManipulation original, Cloner cloner) : base(original, cloner) { }
58    public RemoveBranchManipulation()
59      : base() {
60      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeLengthParameterName, "The maximal length (number of nodes) of the symbolic expression tree."));
61      Parameters.Add(new ValueLookupParameter<IntValue>(MaximumSymbolicExpressionTreeDepthParameterName, "The maximal depth of the symbolic expression tree (a tree with one node has depth = 0)."));
62    }
63
64    public override IDeepCloneable Clone(Cloner cloner) {
65      return new RemoveBranchManipulation(this, cloner);
66    }
67
68    protected override void Manipulate(IRandom random, ISymbolicExpressionTree symbolicExpressionTree) {
69      RemoveRandomBranch(random, symbolicExpressionTree, MaximumSymbolicExpressionTreeLength.Value, MaximumSymbolicExpressionTreeDepth.Value);
70    }
71
72    public static void RemoveRandomBranch(IRandom random, ISymbolicExpressionTree symbolicExpressionTree, int maxTreeLength, int maxTreeDepth) {
73      var allowedSymbols = new List<ISymbol>();
74      ISymbolicExpressionTreeNode parent;
75      int childIndex;
76      int maxLength;
77      int maxDepth;
78      // repeat until a fitting parent and child are found (MAX_TRIES times)
79      int tries = 0;
80
81      var nodes = symbolicExpressionTree.Root.IterateNodesPrefix().Skip(1).Where(n => n.SubtreeCount > 0).ToList();
82      do {
83        parent = nodes.SampleRandom(random);
84
85        childIndex = random.Next(parent.SubtreeCount);
86        var child = parent.GetSubtree(childIndex);
87        maxLength = maxTreeLength - symbolicExpressionTree.Length + child.GetLength();
88        maxDepth = maxTreeDepth - symbolicExpressionTree.Depth + child.GetDepth();
89
90        allowedSymbols.Clear();
91        foreach (var symbol in parent.Grammar.GetAllowedChildSymbols(parent.Symbol, childIndex)) {
92          // check basic properties that the new symbol must have
93          if (symbol.Name != child.Symbol.Name &&
94            symbol.InitialFrequency > 0 &&
95            parent.Grammar.GetMinimumExpressionDepth(symbol) + 1 <= maxDepth &&
96            parent.Grammar.GetMinimumExpressionLength(symbol) <= maxLength) {
97            allowedSymbols.Add(symbol);
98          }
99        }
100        tries++;
101      } while (tries < MAX_TRIES && allowedSymbols.Count == 0);
102
103      if (tries >= MAX_TRIES) return;
104      ReplaceWithMinimalTree(random, symbolicExpressionTree.Root, parent, childIndex);
105    }
106
107    private static void ReplaceWithMinimalTree(IRandom random, ISymbolicExpressionTreeNode root, ISymbolicExpressionTreeNode parent, int childIndex) {
108      // determine possible symbols that will lead to the smallest possible tree
109      var possibleSymbols = (from s in parent.Grammar.GetAllowedChildSymbols(parent.Symbol, childIndex)
110                             where s.InitialFrequency > 0.0
111                             group s by parent.Grammar.GetMinimumExpressionLength(s) into g
112                             orderby g.Key
113                             select g).First().ToList();
114      var weights = possibleSymbols.Select(x => x.InitialFrequency).ToList();
115
116#pragma warning disable 612, 618
117      var selectedSymbol = possibleSymbols.SelectRandom(weights, random);
118#pragma warning restore 612, 618
119
120      var newTreeNode = selectedSymbol.CreateTreeNode();
121      if (newTreeNode.HasLocalParameters) newTreeNode.ResetLocalParameters(random);
122      parent.RemoveSubtree(childIndex);
123      parent.InsertSubtree(childIndex, newTreeNode);
124
125      var topLevelNode = newTreeNode as SymbolicExpressionTreeTopLevelNode;
126      if (topLevelNode != null)
127        topLevelNode.SetGrammar((ISymbolicExpressionTreeGrammar)root.Grammar.Clone());
128
129      for (int i = 0; i < newTreeNode.Grammar.GetMinimumSubtreeCount(newTreeNode.Symbol); i++) {
130        // insert a dummy sub-tree and add the pending extension to the list
131        var dummy = new SymbolicExpressionTreeNode();
132        newTreeNode.AddSubtree(dummy);
133        // replace the just inserted dummy by recursive application
134        ReplaceWithMinimalTree(random, root, newTreeNode, i);
135      }
136    }
137  }
138}
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