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

java.lang.Object
  extended by 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 1385297 2012-09-16 16:05:57Z tn $
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


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