source: branches/PersistenceOverhaul/HeuristicLab.Encodings.PermutationEncoding/3.3/Crossovers/CyclicCrossover.cs @ 13325

Last change on this file since 13325 was 12012, checked in by ascheibe, 5 years ago

#2212 merged r12008, r12009, r12010 back into trunk

File size: 6.3 KB
Line 
1#region License Information
2/* HeuristicLab
3 * Copyright (C) 2002-2015 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.Common;
24using HeuristicLab.Core;
25using HeuristicLab.Persistence.Default.CompositeSerializers.Storable;
26
27namespace HeuristicLab.Encodings.PermutationEncoding {
28  /// <summary>
29  /// An operator which performs the cyclic crossover on two permutations.
30  /// </summary>
31  /// <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 />
32  /// The operator first determines all cycles in the permutation and then composes the offspring by alternating between the cycles of the two parents.
33  /// </remarks>
34  [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.")]
35  [StorableClass]
36  public class CyclicCrossover : PermutationCrossover {
37    [StorableConstructor]
38    protected CyclicCrossover(bool deserializing) : base(deserializing) { }
39    protected CyclicCrossover(CyclicCrossover original, Cloner cloner) : base(original, cloner) { }
40    public CyclicCrossover() : base() { }
41
42    public override IDeepCloneable Clone(Cloner cloner) {
43      return new CyclicCrossover(this, cloner);
44    }
45
46    /// <summary>
47    /// Performs the cyclic crossover on <paramref name="parent1"/> and <paramref name="parent2"/>.
48    /// </summary>
49    /// <exception cref="ArgumentException">Thrown when <paramref name="parent1"/> and <paramref name="parent2"/> are not of equal length.</exception>
50    /// <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>
51    /// <remarks>
52    /// First this method randomly determines from which parent to start with equal probability.
53    /// Then it copies the first cycle from the chosen parent starting from index 0 in the permutation.
54    /// 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.
55    /// It continues to switch between parents for each completed cycle until no new cycle is found anymore.<br /><br />
56    /// The stochasticity of this operator is rather low. There are only two possible outcomes for a given pair of parents.
57    /// </remarks>
58    /// <exception cref="ArgumentException">Thrown if the two parents are not of equal length.</exception>
59    /// <param name="random">The random number generator.</param>
60    /// <param name="parent1">The parent scope 1 to cross over.</param>
61    /// <param name="parent2">The parent scope 2 to cross over.</param>
62    /// <returns>The created cross over permutation as int array.</returns>
63    public static Permutation Apply(IRandom random, Permutation parent1, Permutation parent2) {
64      if (parent1.Length != parent2.Length) throw new ArgumentException("CyclicCrossover: The parent permutations are of unequal length.");
65      int length = parent1.Length;
66      int[] result = new int[length];
67      bool[] indexCopied = new bool[length];
68      int[] invParent1 = new int[length];
69      int[] invParent2 = new int[length];
70
71      // calculate inverse mappings (number -> index) for parent1 and parent2
72      try {
73        for (int i = 0; i < length; i++) {
74          invParent1[parent1[i]] = i;
75          invParent2[parent2[i]] = i;
76        }
77      }
78      catch (IndexOutOfRangeException) {
79        throw new InvalidOperationException("CyclicCrossover: The permutation must consist of numbers in the interval [0;N) with N = length of the permutation.");
80      }
81
82      // randomly choose whether to start copying from parent1 or parent2
83      bool copyFromParent1 = ((random.NextDouble() < 0.5) ? (false) : (true));
84
85      int j = 0;
86      do {
87        do {
88          if (copyFromParent1) {
89            result[j] = parent1[j]; // copy number at position j from parent1
90            indexCopied[j] = true;
91            j = invParent2[result[j]]; // set position j to the position of the copied number in parent2
92          } else {
93            result[j] = parent2[j]; // copy number at position j from parent2
94            indexCopied[j] = true;
95            j = invParent1[result[j]]; // set position j to the position of the copied number in parent1
96          }
97        } while (!indexCopied[j]);
98        copyFromParent1 = !copyFromParent1;
99        j = 0;
100        while (j < length && indexCopied[j]) j++;
101      } while (j < length);
102
103      return new Permutation(parent1.PermutationType, result);
104    }
105
106    /// <summary>
107    /// Checks number of parents and calls <see cref="Apply(IRandom, Permutation, Permutation)"/>.
108    /// </summary>
109    /// <exception cref="InvalidOperationException">Thrown if there are not exactly two parents.</exception>
110    /// <param name="random">A random number generator.</param>
111    /// <param name="parents">An array containing the two permutations that should be crossed.</param>
112    /// <returns>The newly created permutation, resulting from the crossover operation.</returns>
113    protected override Permutation Cross(IRandom random, ItemArray<Permutation> parents) {
114      if (parents.Length != 2) throw new InvalidOperationException("CyclicCrossover: The number of parents is not equal to 2.");
115      return Apply(random, parents[0], parents[1]);
116    }
117  }
118}
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