org.apache.commons.math3.genetics

Class UniformCrossover<T>

java.lang.Object

org.apache.commons.math3.genetics.UniformCrossover<T>

Type Parameters:

T - generic type of the AbstractListChromosomes for crossover

All Implemented Interfaces:

CrossoverPolicy

public class UniformCrossover<T>
extends java.lang.Object
implements CrossoverPolicy

Perform Uniform Crossover [UX] on the specified chromosomes. A fixed mixing ratio is used to combine genes from the first and second parents, e.g. using a ratio of 0.5 would result in approximately 50% of genes coming from each parent. This is typically a poor method of crossover, but empirical evidence suggests that it is more exploratory and results in a larger part of the problem space being searched.

This crossover policy evaluates each gene of the parent chromosomes by chosing a uniform random number p in the range [0, 1]. If p < ratio, the parent genes are swapped. This means with a ratio of 0.7, 30% of the genes from the first parent and 70% from the second parent will be selected for the first offspring (and vice versa for the second offspring).

This policy works only on AbstractListChromosome, and therefore it is parameterized by T. Moreover, the chromosomes must have same lengths.

Since:

3.1

See Also:

Crossover techniques (Wikipedia), Crossover (Obitko.com), Uniform crossover

Field Summary

Fields

Modifier and Type	Field and Description
private double	ratio The mixing ratio.

Constructor Summary

Constructors

Constructor and Description
UniformCrossover(double ratio) Creates a new UniformCrossover policy using the given mixing ratio.

Method Summary

Modifier and Type	Method and Description
ChromosomePair	crossover(Chromosome first, Chromosome second) Perform a crossover operation on the given chromosomes.
double	getRatio() Returns the mixing ratio used by this CrossoverPolicy.
private ChromosomePair	mate(AbstractListChromosome<T> first, AbstractListChromosome<T> second) Helper for crossover(Chromosome, Chromosome).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

ratio

private final double ratio

The mixing ratio.

Constructor Detail

UniformCrossover

public UniformCrossover(double ratio)
                 throws OutOfRangeException

Creates a new UniformCrossover policy using the given mixing ratio.

Parameters:

ratio - the mixing ratio

Throws:

OutOfRangeException - if the mixing ratio is outside the [0, 1] range

Method Detail

getRatio

public double getRatio()

Returns the mixing ratio used by this CrossoverPolicy.

Returns:

the mixing ratio

crossover

public ChromosomePair crossover(Chromosome first,
                                Chromosome second)
                         throws DimensionMismatchException,
                                MathIllegalArgumentException

Perform a crossover operation on the given chromosomes.

Specified by:

crossover in interface CrossoverPolicy

Parameters:

first - the first chromosome.

second - the second chromosome.

Returns:

the pair of new chromosomes that resulted from the crossover.

Throws:

MathIllegalArgumentException - iff one of the chromosomes is not an instance of AbstractListChromosome

DimensionMismatchException - if the length of the two chromosomes is different

mate

private ChromosomePair mate(AbstractListChromosome<T> first,
                            AbstractListChromosome<T> second)
                     throws DimensionMismatchException

Helper for crossover(Chromosome, Chromosome). Performs the actual crossover.

Parameters:

first - the first chromosome

second - the second chromosome

Returns:

the pair of new chromosomes that resulted from the crossover

Throws:

DimensionMismatchException - if the length of the two chromosomes is different