org.apache.commons.math3.genetics
Class CycleCrossover<T>

java.lang.Object
  org.apache.commons.math3.genetics.CycleCrossover<T>

Type Parameters:

T - generic type of the AbstractListChromosomes for crossover

All Implemented Interfaces:

CrossoverPolicy

public class CycleCrossover<T>
extends Object
implements CrossoverPolicy

Cycle Crossover [CX] builds offspring from ordered chromosomes by identifying cycles between two parent chromosomes. To form the children, the cycles are copied from the respective parents.

To form a cycle the following procedure is applied:

1. start with the first gene of parent 1
2. look at the gene at the same position of parent 2
3. go to the position with the same gene in parent 1
4. add this gene index to the cycle
5. repeat the steps 2-5 until we arrive at the starting gene of this cycle

The indices that form a cycle are then used to form the children in alternating order, i.e. in cycle 1, the genes of parent 1 are copied to child 1, while in cycle 2 the genes of parent 1 are copied to child 2, and so forth ...

Example (zero-start cycle):

 p1 = (8 4 7 3 6 2 5 1 9 0)    X   c1 = (8 1 2 3 4 5 6 7 9 0)
 p2 = (0 1 2 3 4 5 6 7 8 9)    X   c2 = (0 4 7 3 6 2 5 1 8 9)

 cycle 1: 8 0 9
 cycle 2: 4 1 7 2 5 6
 cycle 3: 3
 

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

Since:

3.1

Version:

$Id: CycleCrossover.java 7721 2013-02-14 14:07:13Z CardosoP $

See Also:

Cycle Crossover Operator

Constructor Summary

CycleCrossover()
Creates a new CycleCrossover policy.

CycleCrossover(boolean randomStart)
Creates a new CycleCrossover policy using the given randomStart behavior.

Method Summary

ChromosomePair	crossover(Chromosome first, Chromosome second) Perform a crossover operation on the given chromosomes.
boolean	isRandomStart() Returns whether the starting index is chosen randomly or set to zero.
protected 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

Constructor Detail

CycleCrossover

public CycleCrossover()

Creates a new CycleCrossover policy.

CycleCrossover

public CycleCrossover(boolean randomStart)

Creates a new CycleCrossover policy using the given randomStart behavior.

Parameters:

randomStart - whether the start index shall be chosen randomly or be set to 0

Method Detail

isRandomStart

public boolean isRandomStart()

Returns whether the starting index is chosen randomly or set to zero.

Returns:

true if the starting index is chosen randomly, false otherwise

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 - if the chromosomes are not an instance of AbstractListChromosome

DimensionMismatchException - if the length of the two chromosomes is different

mate

protected 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