org.jgap.impl
Class SwappingMutationOperator

java.lang.Object
  org.jgap.BaseGeneticOperator
      org.jgap.impl.MutationOperator
          org.jgap.impl.SwappingMutationOperator

All Implemented Interfaces:

java.io.Serializable, java.lang.Comparable, Configurable, GeneticOperator

public class SwappingMutationOperator
extends MutationOperator

Swaps the genes instead of mutating them. This kind of operator is required by Traveling Salesman Problem. See J. Grefenstette, R. Gopal, R. Rosmaita, and D. Gucht. Genetic algorithms for the traveling salesman problem. In Proceedings of the Second International Conference on Genetic Algorithms. Lawrence Eribaum Associates, Mahwah, NJ, 1985. and also Sushil J. Louis & Gong Li }

Since:

2.0

See Also:

Serialized Form

Constructor Summary

SwappingMutationOperator()
Constructs a new instance of this operator.

SwappingMutationOperator(Configuration a_config)

SwappingMutationOperator(Configuration a_config, int a_desiredMutationRate)
Constructs a new instance of this MutationOperator with the given mutation rate.

SwappingMutationOperator(Configuration a_config, IUniversalRateCalculator a_mutationRateCalculator)
Constructs a new instance of this operator with a specified mutation rate calculator, which results in dynamic mutation being turned on.

Method Summary

int	getStartOffset() Gets a number of genes at the start of chromosome, that are excluded from the swapping.
protected IChromosome	operate(IChromosome a_x, int a_rate, RandomGenerator a_generator) Operate on the given chromosome with the given mutation rate.
void	operate(Population a_population, java.util.List a_candidateChromosomes) The operate method will be invoked on each of the genetic operators referenced by the current Configuration object during the evolution phase.
protected Gene[]	operate(RandomGenerator a_generator, int a_target_gene, Gene[] a_genes) Operate on the given array of genes.
void	setStartOffset(int a_offset) Sets a number of genes at the start of chromosome, that are excluded from the swapping.

Methods inherited from class org.jgap.impl.MutationOperator

compareTo, equals, getMutationRate, getMutationRateCalc, setMutationRateCalc

Methods inherited from class org.jgap.BaseGeneticOperator

getConfiguration

Methods inherited from class java.lang.Object

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

Constructor Detail

SwappingMutationOperator

public SwappingMutationOperator()
                         throws InvalidConfigurationException

Constructs a new instance of this operator.

Attention: The configuration used is the one set with the static method Genotype.setConfiguration.

Throws:

InvalidConfigurationException

SwappingMutationOperator

public SwappingMutationOperator(Configuration a_config)
                         throws InvalidConfigurationException

Parameters:

a_config - the configuration to use

Throws:

InvalidConfigurationException

Since:

3.0

SwappingMutationOperator

public SwappingMutationOperator(Configuration a_config,
                                IUniversalRateCalculator a_mutationRateCalculator)
                         throws InvalidConfigurationException

Constructs a new instance of this operator with a specified mutation rate calculator, which results in dynamic mutation being turned on.

Parameters:

a_config - the configuration to use

a_mutationRateCalculator - calculator for dynamic mutation rate computation

Throws:

InvalidConfigurationException

Since:

3.0 (previously: without a_config)

SwappingMutationOperator

public SwappingMutationOperator(Configuration a_config,
                                int a_desiredMutationRate)
                         throws InvalidConfigurationException

Constructs a new instance of this MutationOperator with the given mutation rate.

Parameters:

a_config - the configuration to use

a_desiredMutationRate - desired rate of mutation, expressed as the denominator of the 1 / X fraction. For example, 1000 would result in 1/1000 genes being mutated on average. A mutation rate of zero disables mutation entirely

Throws:

InvalidConfigurationException

Since:

3.0 (previously: without a_config)

Method Detail

operate

public void operate(Population a_population,
                    java.util.List a_candidateChromosomes)

Description copied from interface: GeneticOperator

The operate method will be invoked on each of the genetic operators referenced by the current Configuration object during the evolution phase. Operators are given an opportunity to run in the order that they are added to the Configuration. Implementations of this method may reference the population of Chromosomes as it was at the beginning of the evolutionary phase and/or they may instead reference the candidate Chromosomes, which are the results of prior genetic operators. In either case, only Chromosomes added to the list of candidate chromosomes will be considered for natural selection.

The parameters a_population and a_candidateChromosomes may refer to the same list of chromosomes for performance issues. Thus would mean an in-place modification. In ealier JGAP versions it was suggested never modifying the input population. Please refer to implementations delivered with JGAP to get a picture of the way non-susceptible in-place modifications are possible. If wrongly done, ConcurrentModificationException could be risen when accessing the population by an iterator in a GeneticOperator. Or, if population.getChromosomes().size() was used inside a loop where chromosomes were added to the input population this could lead to an infinite loop in worst case.

Specified by:

operate in interface GeneticOperator

Overrides:

operate in class MutationOperator

Parameters:

a_population - the population of chromosomes from the current evolution prior to exposure to any genetic operators. Chromosomes in this array should not be modified. Please, notice, that the call in Genotype.evolve() to the implementations of GeneticOperator overgoes this due to performance issues

a_candidateChromosomes - the pool of chromosomes that have been selected for the next evolved population

Since:

2.0

operate

protected IChromosome operate(IChromosome a_x,
                              int a_rate,
                              RandomGenerator a_generator)

Operate on the given chromosome with the given mutation rate.

Parameters:

a_x - chromosome to operate

a_rate - mutation rate

a_generator - random generator to use (must not be null)

Returns:

mutated chromosome of null if no mutation has occured.

Since:

2.0

operate

protected Gene[] operate(RandomGenerator a_generator,
                         int a_target_gene,
                         Gene[] a_genes)

Operate on the given array of genes. This method is only called when it is already clear that the mutation must occur under the given mutation rate

Parameters:

a_generator - a random number generator that may be needed to perform a mutation

a_target_gene - an index of gene in the chromosome that will mutate

a_genes - the array of all genes in the chromosome

Returns:

the mutated gene array

Since:

2.0

setStartOffset

public void setStartOffset(int a_offset)

Sets a number of genes at the start of chromosome, that are excluded from the swapping. In the Salesman task, the first city in the list should (where the salesman leaves from) probably should not change as it is part of the list. The default value is 1.

Parameters:

a_offset - the offset to set

Since:

2.0

getStartOffset

public int getStartOffset()

Gets a number of genes at the start of chromosome, that are excluded from the swapping. In the Salesman task, the first city in the list should (where the salesman leaves from) probably should not change as it is part of the list. The default value is 1.

Returns:

the start offset

Since:

2.0