io.jenetics

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

java.lang.Object

io.jenetics.AbstractAlterer<G,C>

io.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:

4.0

Author:

Franz Wilhelmstötter

Field Summary

Fields inherited from class io.jenetics.AbstractAlterer

_probability

Fields inherited from interface io.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
AltererResult<G,C>	alter(Seq<Phenotype<G,C>> population, long generation) Concrete implementation of the alter method.
protected MutatorResult<Chromosome<G>>	mutate(Chromosome<G> chromosome, double p, Random random) Mutates the given chromosome.
protected MutatorResult<Genotype<G>>	mutate(Genotype<G> genotype, double p, Random random) Mutates the given genotype.
protected G	mutate(G gene, Random random) Mutates the given gene.
protected MutatorResult<Phenotype<G,C>>	mutate(Phenotype<G,C> phenotype, long generation, double p, Random random) Mutates the given phenotype.
String	toString()

Methods inherited from class io.jenetics.AbstractAlterer

getProbability

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface io.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 AltererResult<G,C> alter(Seq<Phenotype<G,C>> population,
                                long generation)

Concrete implementation of the alter method. It uses the following mutation methods: mutate(Phenotype, long, double, Random), mutate(Genotype, double, Random), mutate(Chromosome, double, Random), mutate(Gene, Random), in this specific order.

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 alter-result object, which contains the altered population and the alteration count

See Also:

mutate(Phenotype, long, double, Random), mutate(Genotype, double, Random), mutate(Chromosome, double, Random), mutate(Gene, Random)

mutate

protected MutatorResult<Phenotype<G,C>> mutate(Phenotype<G,C> phenotype,
                                               long generation,
                                               double p,
                                               Random random)

Mutates the given phenotype.

Parameters:

phenotype - the phenotype to mutate

generation - the actual generation

p - the mutation probability for the underlying genetic objects

random - the random engine used for the phenotype mutation

Returns:

the mutation result

See Also:

mutate(Genotype, double, Random), mutate(Chromosome, double, Random), mutate(Gene, Random)

mutate

protected MutatorResult<Genotype<G>> mutate(Genotype<G> genotype,
                                            double p,
                                            Random random)

Mutates the given genotype.

Parameters:

genotype - the genotype to mutate

p - the mutation probability for the underlying genetic objects

random - the random engine used for the genotype mutation

Returns:

the mutation result

See Also:

mutate(Chromosome, double, Random), mutate(Gene, Random)

mutate

protected MutatorResult<Chromosome<G>> mutate(Chromosome<G> chromosome,
                                              double p,
                                              Random random)

Mutates the given chromosome.

Parameters:

chromosome - the chromosome to mutate

p - the mutation probability for the underlying genetic objects

random - the random engine used for the genotype mutation

Returns:

the mutation result

See Also:

mutate(Gene, Random)

mutate

protected G mutate(G gene,
                   Random random)

Mutates the given gene.

Parameters:

gene - the gene to mutate

random - the random engine used for the genotype mutation

Returns:

the mutation result

toString

public String toString()

Overrides:

toString in class Object