#region License Information
/* HeuristicLab
* Copyright (C) Heuristic and Evolutionary Algorithms Laboratory (HEAL)
*
* This file is part of HeuristicLab.
*
* HeuristicLab is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* HeuristicLab is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with HeuristicLab. If not, see .
*/
#endregion
using System;
using HeuristicLab.Common;
using HeuristicLab.Core;
using HEAL.Attic;
namespace HeuristicLab.Encodings.PermutationEncoding {
///
/// 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.
/// The operator first determines all cycles in the permutation and then composes the offspring by alternating between the cycles of the two parents.
///
[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.")]
[StorableType("7C4797B7-A154-4702-AEEB-5511A170858B")]
public class CyclicCrossover : PermutationCrossover {
[StorableConstructor]
protected CyclicCrossover(StorableConstructorFlag _) : base(_) { }
protected CyclicCrossover(CyclicCrossover original, Cloner cloner) : base(original, cloner) { }
public CyclicCrossover() : base() { }
public override IDeepCloneable Clone(Cloner cloner) {
return new CyclicCrossover(this, cloner);
}
///
/// Performs the cyclic crossover on and .
///
/// Thrown when and are not of equal length.
/// Thrown if the numbers in the permutation elements are not in the range [0;N) with N = length of the permutation.
///
/// First this method randomly determines from which parent to start with equal probability.
/// Then it copies the first cycle from the chosen parent starting from index 0 in the permutation.
/// 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.
/// It continues to switch between parents for each completed cycle until no new cycle is found anymore.
/// The stochasticity of this operator is rather low. There are only two possible outcomes for a given pair of parents.
///
/// Thrown if the two parents are not of equal length.
/// The random number generator.
/// The parent scope 1 to cross over.
/// The parent scope 2 to cross over.
/// The created cross over permutation as int array.
public static Permutation Apply(IRandom random, Permutation parent1, Permutation parent2) {
if (parent1.Length != parent2.Length) throw new ArgumentException("CyclicCrossover: The parent permutations are of unequal length.");
int length = parent1.Length;
int[] result = new int[length];
bool[] indexCopied = new bool[length];
int[] invParent1 = new int[length];
int[] invParent2 = new int[length];
// calculate inverse mappings (number -> index) for parent1 and parent2
try {
for (int i = 0; i < length; i++) {
invParent1[parent1[i]] = i;
invParent2[parent2[i]] = i;
}
}
catch (IndexOutOfRangeException) {
throw new InvalidOperationException("CyclicCrossover: The permutation must consist of numbers in the interval [0;N) with N = length of the permutation.");
}
// randomly choose whether to start copying from parent1 or parent2
bool copyFromParent1 = ((random.NextDouble() < 0.5) ? (false) : (true));
int j = 0;
do {
do {
if (copyFromParent1) {
result[j] = parent1[j]; // copy number at position j from parent1
indexCopied[j] = true;
j = invParent2[result[j]]; // set position j to the position of the copied number in parent2
} else {
result[j] = parent2[j]; // copy number at position j from parent2
indexCopied[j] = true;
j = invParent1[result[j]]; // set position j to the position of the copied number in parent1
}
} while (!indexCopied[j]);
copyFromParent1 = !copyFromParent1;
j = 0;
while (j < length && indexCopied[j]) j++;
} while (j < length);
return new Permutation(parent1.PermutationType, result);
}
///
/// Checks number of parents and calls .
///
/// Thrown if there are not exactly two parents.
/// A random number generator.
/// An array containing the two permutations that should be crossed.
/// The newly created permutation, resulting from the crossover operation.
protected override Permutation Cross(IRandom random, ItemArray parents) {
if (parents.Length != 2) throw new InvalidOperationException("CyclicCrossover: The number of parents is not equal to 2.");
return Apply(random, parents[0], parents[1]);
}
}
}