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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using GeneticSharp.Domain.Chromosomes;
using GeneticSharp.Domain.Randomizations;
namespace GeneticSharp.Domain.Crossovers
{
/// <summary>
/// Partially mapped crossover (PMX).
/// <remarks>
/// The partially-mapped crossover operator was suggested by Gold- berg and Lingle (1985).
/// It passes on ordering and value information from the parent tours to the offspring tours.
/// A portion of one parent’s string is mapped onto a portion of the other parent’s string and the remaining information is exchanged.
/// <see href="http://lev4projdissertation.googlecode.com/svn-history/r100/trunk/reading/read/aiRev99.pdf">Genetic Algorithms for the Travelling Salesman Problem - A Review of Representations and Operators</see>
/// </remarks>
/// </summary>
[DisplayName("Partially Mapped (PMX)")]
public class PartiallyMappedCrossover : CrossoverBase
{
#region Constructors
/// <summary>
/// Initializes a new instance of the <see cref="GeneticSharp.Domain.Crossovers.PartiallyMappedCrossover"/> class.
/// </summary>
public PartiallyMappedCrossover() : base(2, 2, 3)
{
IsOrdered = true;
}
#endregion
#region Methods
/// <summary>
/// Performs the cross with specified parents generating the children.
/// </summary>
/// <param name="parents">The parents chromosomes.</param>
/// <returns>
/// The offspring (children) of the parents.
/// </returns>
protected override IList<IChromosome> PerformCross(IList<IChromosome> parents)
{
if (parents.AnyHasRepeatedGene())
{
throw new CrossoverException(this, "The Partially Mapped Crossover (PMX) can be only used with ordered chromosomes. The specified chromosome has repeated genes.");
}
var parent1 = parents[0];
var parent2 = parents[1];
var cutPointsIndexes = RandomizationProvider.Current.GetUniqueInts(2, 0, parent1.Length);
Array.Sort(cutPointsIndexes);
var firstCutPointIndex = cutPointsIndexes[0];
var secondCutPointIdnex = cutPointsIndexes[1];
var parent1Genes = parent1.GetGenes();
var parent1MappingSection = parent1Genes.Skip(firstCutPointIndex).Take((secondCutPointIdnex - firstCutPointIndex) + 1).ToArray();
var parent2Genes = parent2.GetGenes();
var parent2MappingSection = parent2Genes.Skip(firstCutPointIndex).Take((secondCutPointIdnex - firstCutPointIndex) + 1).ToArray();
var offspring1 = parent1.CreateNew();
var offspring2 = parent2.CreateNew();
offspring2.ReplaceGenes(firstCutPointIndex, parent1MappingSection);
offspring1.ReplaceGenes(firstCutPointIndex, parent2MappingSection);
var length = parent1.Length;
for (int i = 0; i < length; i++)
{
if (i >= firstCutPointIndex && i <= secondCutPointIdnex)
{
continue;
}
var geneForoffspring1 = GetGeneNotInMappingSection(parent1Genes[i], parent2MappingSection, parent1MappingSection);
offspring1.ReplaceGene(i, geneForoffspring1);
var geneForoffspring2 = GetGeneNotInMappingSection(parent2Genes[i], parent1MappingSection, parent2MappingSection);
offspring2.ReplaceGene(i, geneForoffspring2);
}
return new List<IChromosome>() { offspring1, offspring2 };
}
private Gene GetGeneNotInMappingSection(Gene candidateGene, Gene[] mappingSection, Gene[] otherParentMappingSection)
{
var indexOnMappingSection = mappingSection
.Select((item, index) => new { Gene = item, Index = index })
.FirstOrDefault(g => g.Gene.Equals(candidateGene));
if (indexOnMappingSection != null)
{
return GetGeneNotInMappingSection(otherParentMappingSection[indexOnMappingSection.Index], mappingSection, otherParentMappingSection);
}
return candidateGene;
}
#endregion
}
}