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source: branches/CloningRefactoring/HeuristicLab.Encodings.PermutationEncoding/3.3/Crossovers/CyclicCrossover.cs @ 4656

Last change on this file since 4656 was 4477, checked in by gkronber, 14 years ago

Merged r4458, r4459,r4462,r4464 from data analysis exploration branch into trunk. #1142

File size: 5.9 KB
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1#region License Information
2/* HeuristicLab
3 * Copyright (C) 2002-2010 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 HeuristicLab.Core;
24using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
25
26namespace HeuristicLab.Encodings.PermutationEncoding {
27  /// <summary>
28  /// An operator which performs the cyclic crossover on two permutations.
29  /// </summary>
30  /// <remarks>It is implemented as described in Eiben, A.E. and Smith, J.E. 2003. Introduction to Evolutionary Computation. Natural Computing Series, Springer-Verlag Berlin Heidelberg.<br />
31  /// The operator first determines all cycles in the permutation and then composes the offspring by alternating between the cycles of the two parents.
32  /// </remarks>
33  [Item("CyclicCrossover", "An operator which performs the cyclic crossover on two permutations. It is implemented as described in Eiben, A.E. and Smith, J.E. 2003. Introduction to Evolutionary Computation. Natural Computing Series, Springer-Verlag Berlin Heidelberg.")]
34  [StorableClass]
35  public class CyclicCrossover : PermutationCrossover {
36    /// <summary>
37    /// Performs the cyclic crossover on <paramref name="parent1"/> and <paramref name="parent2"/>.
38    /// </summary>
39    /// <exception cref="ArgumentException">Thrown when <paramref name="parent1"/> and <paramref name="parent2"/> are not of equal length.</exception>
40    /// <exception cref="InvalidOperationException">Thrown if the numbers in the permutation elements are not in the range [0;N) with N = length of the permutation.</exception>
41    /// <remarks>
42    /// First this method randomly determines from which parent to start with equal probability.
43    /// Then it copies the first cycle from the chosen parent starting from index 0 in the permutation.
44    /// After the cycle is complete it copies the next cycle starting from the index closest to 0 which was not yet copied from the other parent.
45    /// It continues to switch between parents for each completed cycle until no new cycle is found anymore.<br /><br />
46    /// The stochasticity of this operator is rather low. There are only two possible outcomes for a given pair of parents.
47    /// </remarks>
48    /// <exception cref="ArgumentException">Thrown if the two parents are not of equal length.</exception>
49    /// <param name="random">The random number generator.</param>
50    /// <param name="parent1">The parent scope 1 to cross over.</param>
51    /// <param name="parent2">The parent scope 2 to cross over.</param>
52    /// <returns>The created cross over permutation as int array.</returns>
53    public static Permutation Apply(IRandom random, Permutation parent1, Permutation parent2) {
54      if (parent1.Length != parent2.Length) throw new ArgumentException("CyclicCrossover: The parent permutations are of unequal length.");
55      int length = parent1.Length;
56      int[] result = new int[length];
57      bool[] indexCopied = new bool[length];
58      int[] invParent1 = new int[length];
59      int[] invParent2 = new int[length];
60
61      // calculate inverse mappings (number -> index) for parent1 and parent2
62      try {
63        for (int i = 0; i < length; i++) {
64          invParent1[parent1[i]] = i;
65          invParent2[parent2[i]] = i;
66        }
67      }
68      catch (IndexOutOfRangeException) {
69        throw new InvalidOperationException("CyclicCrossover: The permutation must consist of numbers in the interval [0;N) with N = length of the permutation.");
70      }
71
72      // randomly choose whether to start copying from parent1 or parent2
73      bool copyFromParent1 = ((random.NextDouble() < 0.5) ? (false) : (true));
74
75      int j = 0;
76      do {
77        do {
78          if (copyFromParent1) {
79            result[j] = parent1[j]; // copy number at position j from parent1
80            indexCopied[j] = true;
81            j = invParent2[result[j]]; // set position j to the position of the copied number in parent2
82          } else {
83            result[j] = parent2[j]; // copy number at position j from parent2
84            indexCopied[j] = true;
85            j = invParent1[result[j]]; // set position j to the position of the copied number in parent1
86          }
87        } while (!indexCopied[j]);
88        copyFromParent1 = !copyFromParent1;
89        j = 0;
90        while (j < length && indexCopied[j]) j++;
91      } while (j < length);
92
93      return new Permutation(parent1.PermutationType, result);
94    }
95
96    /// <summary>
97    /// Checks number of parents and calls <see cref="Apply(IRandom, Permutation, Permutation)"/>.
98    /// </summary>
99    /// <exception cref="InvalidOperationException">Thrown if there are not exactly two parents.</exception>
100    /// <param name="random">A random number generator.</param>
101    /// <param name="parents">An array containing the two permutations that should be crossed.</param>
102    /// <returns>The newly created permutation, resulting from the crossover operation.</returns>
103    protected override Permutation Cross(IRandom random, ItemArray<Permutation> parents) {
104      if (parents.Length != 2) throw new InvalidOperationException("CyclicCrossover: The number of parents is not equal to 2.");
105      return Apply(random, parents[0], parents[1]);
106    }
107  }
108}
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