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 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
  See Also:
    Cycle Crossover Operator

- - ### 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
    Modifier and Type | Method and Description
    --- | ---
    `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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