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source: branches/GrammaticalEvolution/HeuristicLab.Problems.GrammaticalEvolution/Mappers/BreathFirstMapper.cs @ 10276

Last change on this file since 10276 was 10229, checked in by sawinkle, 9 years ago

#2109: Implemented a DepthFirstMapper, which works similarly to the DepthFirstMapper, but uses a queue to enable a breath-first tree creation.

File size: 5.5 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;
23using System.Collections.Generic;
24using HeuristicLab.Common;
25using HeuristicLab.Core;
26using HeuristicLab.Encodings.IntegerVectorEncoding;
27using HeuristicLab.Encodings.SymbolicExpressionTreeEncoding;
28using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
29using HeuristicLab.Random;
30
31namespace HeuristicLab.Problems.GrammaticalEvolution {
32  /// <summary>
33  /// BreathFirstMapper
34  /// </summary>
35  [Item("BreathFirstMapper", "Resolves the non-terminal symbols of the resulting phenotypic syntax tree in a breath-first manner.")]
36  [StorableClass]
37  public class BreathFirstMapper : GenotypeToPhenotypeMapper {
38
39    [StorableConstructor]
40    protected BreathFirstMapper(bool deserializing) : base(deserializing) { }
41    protected BreathFirstMapper(BreathFirstMapper original, Cloner cloner) : base(original, cloner) { }
42    public BreathFirstMapper() : base() { }
43
44    public override IDeepCloneable Clone(Cloner cloner) {
45      return new BreathFirstMapper(this, cloner);
46    }
47
48
49    /// <summary>
50    /// Maps a genotype (an integer vector) to a phenotype (a symbolic expression tree).
51    /// Breath-first approach.
52    /// </summary>
53    /// <param name="grammar">grammar definition</param>
54    /// <param name="genotype">integer vector, which should be mapped to a tree</param>
55    /// <returns>phenotype (a symbolic expression tree)</returns>
56    public override SymbolicExpressionTree Map(ISymbolicExpressionGrammar grammar,
57                                               IntegerVector genotype) {
58
59      SymbolicExpressionTree tree = new SymbolicExpressionTree();
60      var rootNode = (SymbolicExpressionTreeTopLevelNode)grammar.ProgramRootSymbol.CreateTreeNode();
61      var startNode = (SymbolicExpressionTreeTopLevelNode)grammar.StartSymbol.CreateTreeNode();
62      rootNode.AddSubtree(startNode);
63      tree.Root = rootNode;
64
65      MapBreathFirstIteratively(startNode, genotype, grammar,
66                                genotype.Length, new MersenneTwister());
67
68      return tree;
69    }
70
71    /// <summary>
72    /// Genotype-to-Phenotype mapper (iterative breath-first approach, by using a queue -> FIFO).
73    /// </summary>
74    /// <param name="startNode">first node of the tree with arity 1</param>
75    /// <param name="genotype">integer vector, which should be mapped to a tree</param>
76    /// <param name="grammar">grammar to determine the allowed child symbols for each node</param>
77    /// <param name="maxSubtreeCount">maximum allowed subtrees (= number of used genomes)</param>
78    /// <param name="random">random number generator</param>
79    private void MapBreathFirstIteratively(ISymbolicExpressionTreeNode startNode,
80                                          IntegerVector genotype,
81                                          ISymbolicExpressionGrammar grammar,
82                                          int maxSubtreeCount, IRandom random) {
83
84      Queue<Tuple<ISymbolicExpressionTreeNode, int>> queue
85        = new Queue<Tuple<ISymbolicExpressionTreeNode, int>>(); // tuples of <node, arity>
86
87      int genotypeIndex = 0;
88      int currSubtreeCount = 1;
89
90      queue.Enqueue(new Tuple<ISymbolicExpressionTreeNode, int>(startNode, 1));
91
92      while ((currSubtreeCount < maxSubtreeCount) && (queue.Count > 0)) {
93
94        Tuple<ISymbolicExpressionTreeNode, int> current = queue.Dequeue();
95
96        // foreach subtree of the current node, create a new node and enqueue it, if it is no terminal node
97        for (int i = 0; i < current.Item2; ++i) {
98
99          var newNode = GetNewChildNode(current.Item1, genotype, grammar, genotypeIndex, random);
100          int arity = SampleArity(random, newNode, maxSubtreeCount - currSubtreeCount);
101
102          if (arity < 0) {
103            current.Item1.AddSubtree(GetRandomTerminalNode(current.Item1, grammar, random));
104          } else {
105            current.Item1.AddSubtree(newNode);
106            genotypeIndex++;
107            currSubtreeCount += arity;
108            if (arity > 0) {
109              // new node has subtrees so enqueue the node
110              queue.Enqueue(new Tuple<ISymbolicExpressionTreeNode, int>(newNode, arity));
111            }
112          }
113        }
114      }
115
116      // maximum allowed subtree count was already reached, but there are still
117      // incomplete subtrees (non-terminal symbols) in the tree
118      // -> fill them with terminal symbols
119      while (queue.Count > 0) {
120        Tuple<ISymbolicExpressionTreeNode, int> current = queue.Dequeue();
121        for (int i = 0; i < current.Item2; ++i) {
122          current.Item1.AddSubtree(GetRandomTerminalNode(current.Item1, grammar, random));
123        }
124      }
125    }
126  }
127}
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