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 `AbstractListChromosome`s for crossover

All Implemented Interfaces:
  CrossoverPolicy

    public class CycleCrossover<T>
    extends java.lang.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

### Field Summary

Fields
`private boolean` `randomStart` If the start index shall be chosen randomly.

### Constructor Summary

Constructors
Constructor and Description
`CycleCrossover()` Creates a new `CycleCrossover` policy.
`CycleCrossover(boolean randomStart)` Creates a new `CycleCrossover` policy using the given `randomStart` behavior.

### Method Summary

Methods
`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`

### Field Detail

#### randomStart

    private final boolean randomStart

If the start index shall be chosen randomly.

### 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