org.jenetics

Class Mutator<G extends Gene<?,G>,C extends Comparable<? super C>>

java.lang.Object

org.jenetics.AbstractAlterer<G,C>

org.jenetics.Mutator<G,C>

All Implemented Interfaces:

Alterer<G,C>

Direct Known Subclasses:

GaussianMutator, SwapMutator

public class Mutator<G extends Gene<?,G>,C extends Comparable<? super C>>
extends AbstractAlterer<G,C>

This class is for mutating a chromosomes of an given population. There are two distinct roles mutation plays

• Exploring the search space. By making small moves mutation allows a population to explore the search space. This exploration is often slow compared to crossover, but in problems where crossover is disruptive this can be an important way to explore the landscape.
• Maintaining diversity. Mutation prevents a population from correlating. Even if most of the search is being performed by crossover, mutation can be vital to provide the diversity which crossover needs.

The mutation probability is the parameter that must be optimized. The optimal value of the mutation rate depends on the role mutation plays. If mutation is the only source of exploration (if there is no crossover) then the mutation rate should be set so that a reasonable neighborhood of solutions is explored.

The mutation probability P(m) is the probability that a specific gene over the whole population is mutated. The number of available genes of an population is

where N_P is the population size, N_g the number of genes of a genotype. So the (average) number of genes mutated by the mutation is

Since:

1.0

Version:

3.0

Author:

Franz Wilhelmstötter

Field Summary

Fields inherited from class org.jenetics.AbstractAlterer

_probability

Fields inherited from interface org.jenetics.Alterer

DEFAULT_ALTER_PROBABILITY

Constructor Summary

Constructors

Constructor and Description
Mutator() Default constructor, with probability = 0.01.
Mutator(double probability) Construct a Mutation object which a given mutation probability.

Method Summary

Modifier and Type	Method and Description
int	alter(Population<G,C> population, long generation) Concrete implementation of the alter method.
boolean	equals(Object obj)
int	hashCode()
protected int	mutate(MSeq<G> genes, double p) Template method which gives an (re)implementation of the mutation class the possibility to perform its own mutation operation, based on a writable gene array and the gene mutation probability p.
String	toString()

Methods inherited from class org.jenetics.AbstractAlterer

getProbability

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface org.jenetics.Alterer

andThen, compose, of

Constructor Detail

Mutator

public Mutator(double probability)

Construct a Mutation object which a given mutation probability.

Parameters:

probability - Mutation probability. The given probability is divided by the number of chromosomes of the genotype to form the concrete mutation probability.

Throws:

IllegalArgumentException - if the probability is not in the valid range of [0, 1]..

Mutator

public Mutator()

Default constructor, with probability = 0.01.

Method Detail

alter

public int alter(Population<G,C> population,
                 long generation)

Concrete implementation of the alter method.

Parameters:

population - The Population to be altered. If the population is null or empty, nothing is altered.

generation - the date of birth (generation) of the altered phenotypes.

Returns:

the number of genes that has been altered.

mutate

protected int mutate(MSeq<G> genes,
                     double p)

Template method which gives an (re)implementation of the mutation class the possibility to perform its own mutation operation, based on a writable gene array and the gene mutation probability p.

Parameters:

genes - the genes to mutate.

p - the gene mutation probability.

Returns:

the number of performed mutations

hashCode

public int hashCode()

Overrides:

hashCode in class AbstractAlterer<G extends Gene<?,G>,C extends Comparable<? super C>>

equals

public boolean equals(Object obj)

Overrides:

equals in class AbstractAlterer<G extends Gene<?,G>,C extends Comparable<? super C>>

toString

public String toString()

Overrides:

toString in class Object