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package org.apache.commons.math3.genetics;

import java.util.ArrayList;
import java.util.List;

import org.apache.commons.math3.exception.DimensionMismatchException;
import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.util.LocalizedFormats;


One point crossover policy. A random crossover point is selected and the first part from each parent is copied to the corresponding child, and the second parts are copied crosswise. Example:
-C- denotes a crossover point
                  -C-                                 -C-
p1 = (1 0 1 0 0 1  | 0 1 1)    X    p2 = (0 1 1 0 1 0  | 1 1 1)
     \------------/ \-----/              \------------/ \-----/
           ||         (*)                       ||        (**)
           VV         (**)                      VV        (*)
     /------------\ /-----\              /------------\ /-----\
c1 = (1 0 1 0 0 1  | 1 1 1)    X    c2 = (0 1 1 0 1 0  | 0 1 1)
This policy works only on AbstractListChromosome, and therefore it is parameterized by T. Moreover, the chromosomes must have same lengths.
Type parameters:
Since:2.0
/** * One point crossover policy. A random crossover point is selected and the * first part from each parent is copied to the corresponding child, and the * second parts are copied crosswise. * * Example: * <pre> * -C- denotes a crossover point * -C- -C- * p1 = (1 0 1 0 0 1 | 0 1 1) X p2 = (0 1 1 0 1 0 | 1 1 1) * \------------/ \-----/ \------------/ \-----/ * || (*) || (**) * VV (**) VV (*) * /------------\ /-----\ /------------\ /-----\ * c1 = (1 0 1 0 0 1 | 1 1 1) X c2 = (0 1 1 0 1 0 | 0 1 1) * </pre> * * This policy works only on {@link AbstractListChromosome}, and therefore it * is parameterized by T. Moreover, the chromosomes must have same lengths. * * @param <T> generic type of the {@link AbstractListChromosome}s for crossover * @since 2.0 * */
public class OnePointCrossover<T> implements CrossoverPolicy {
Performs one point crossover. A random crossover point is selected and the first part from each parent is copied to the corresponding child, and the second parts are copied crosswise. Example:
-C- denotes a crossover point
                  -C-                                 -C-
p1 = (1 0 1 0 0 1  | 0 1 1)    X    p2 = (0 1 1 0 1 0  | 1 1 1)
     \------------/ \-----/              \------------/ \-----/
           ||         (*)                       ||        (**)
           VV         (**)                      VV        (*)
     /------------\ /-----\              /------------\ /-----\
c1 = (1 0 1 0 0 1  | 1 1 1)    X    c2 = (0 1 1 0 1 0  | 0 1 1)
Params:
  • first – first parent (p1)
  • second – second parent (p2)
Throws:
Returns:pair of two children (c1,c2)
/** * Performs one point crossover. A random crossover point is selected and the * first part from each parent is copied to the corresponding child, and the * second parts are copied crosswise. * * Example: * <pre> * -C- denotes a crossover point * -C- -C- * p1 = (1 0 1 0 0 1 | 0 1 1) X p2 = (0 1 1 0 1 0 | 1 1 1) * \------------/ \-----/ \------------/ \-----/ * || (*) || (**) * VV (**) VV (*) * /------------\ /-----\ /------------\ /-----\ * c1 = (1 0 1 0 0 1 | 1 1 1) X c2 = (0 1 1 0 1 0 | 0 1 1) * </pre> * * @param first first parent (p1) * @param second second parent (p2) * @return pair of two children (c1,c2) * @throws MathIllegalArgumentException iff one of the chromosomes is * not an instance of {@link AbstractListChromosome} * @throws DimensionMismatchException if the length of the two chromosomes is different */
@SuppressWarnings("unchecked") // OK because of instanceof checks public ChromosomePair crossover(final Chromosome first, final Chromosome second) throws DimensionMismatchException, MathIllegalArgumentException { if (! (first instanceof AbstractListChromosome<?> && second instanceof AbstractListChromosome<?>)) { throw new MathIllegalArgumentException(LocalizedFormats.INVALID_FIXED_LENGTH_CHROMOSOME); } return crossover((AbstractListChromosome<T>) first, (AbstractListChromosome<T>) second); }
Helper for crossover(Chromosome, Chromosome). Performs the actual crossover.
Params:
  • first – the first chromosome.
  • second – the second chromosome.
Throws:
Returns:the pair of new chromosomes that resulted from the crossover.
/** * Helper for {@link #crossover(Chromosome, Chromosome)}. Performs the actual crossover. * * @param first the first chromosome. * @param second the second chromosome. * @return the pair of new chromosomes that resulted from the crossover. * @throws DimensionMismatchException if the length of the two chromosomes is different */
private ChromosomePair crossover(final AbstractListChromosome<T> first, final AbstractListChromosome<T> second) throws DimensionMismatchException { final int length = first.getLength(); if (length != second.getLength()) { throw new DimensionMismatchException(second.getLength(), length); } // array representations of the parents final List<T> parent1Rep = first.getRepresentation(); final List<T> parent2Rep = second.getRepresentation(); // and of the children final List<T> child1Rep = new ArrayList<T>(length); final List<T> child2Rep = new ArrayList<T>(length); // select a crossover point at random (0 and length makes no sense) final int crossoverIndex = 1 + (GeneticAlgorithm.getRandomGenerator().nextInt(length-2)); // copy the first part for (int i = 0; i < crossoverIndex; i++) { child1Rep.add(parent1Rep.get(i)); child2Rep.add(parent2Rep.get(i)); } // and switch the second part for (int i = crossoverIndex; i < length; i++) { child1Rep.add(parent2Rep.get(i)); child2Rep.add(parent1Rep.get(i)); } return new ChromosomePair(first.newFixedLengthChromosome(child1Rep), second.newFixedLengthChromosome(child2Rep)); } }