Module org.cicirello.chips_n_salsa

Package org.cicirello.search.operators.reals

Class GaussianMutation<T extends RealValued>

java.lang.Object

org.cicirello.search.operators.reals.GaussianMutation<T>

Type Parameters:

T - The specific RealValued type.

All Implemented Interfaces:

Splittable<MutationOperator<T>>, MutationOperator<T>, RealValued, Copyable<GaussianMutation<T>>

public class GaussianMutation<T extends RealValued>
extends Object
implements Copyable<GaussianMutation<T>>

This class implements Gaussian mutation. Gaussian mutation is for mutating floating-point values. This class can be used to mutate objects of any of the classes that implement the RealValued interface, including both univariate and multivariate function input objects.

In a Gaussian mutation, a value v is mutated by adding a randomly generated m such that m is drawn from a Gaussian distribution with mean 0 and standard deviation sigma. It is commonly employed in Evolution Strategies when mutating real valued parameters.

This mutation operator also implements the RealValued interface to enable implementation of metaheuristics that mutate their own mutation parameters. That is, you can pass a GaussianMutation object to the MutationOperator.mutate(T) method of a GaussianMutation object.

To construct a GaussianMutation, you must use one of the factory methods. See the various createGaussianMutation() methods.

Gaussian mutation was introduced in the following article:
Hinterding, R. 1995. Gaussian mutation and self-adaption for numeric genetic algorithms. In IEEE CEC. IEEE Press. 384–389.

Method Summary

Modifier and Type	Method	Description
GaussianMutation<T>	copy()	Creates an identical copy of this object.
static <T extends RealValued> GaussianMutation<T>	createGaussianMutation()	Creates a Gaussian mutation operator with standard deviation equal to 1.
static <T extends RealValued> GaussianMutation<T>	createGaussianMutation(double sigma)	Creates a Gaussian mutation operator.
static <T extends RealValued> GaussianMutation<T>	createGaussianMutation(double sigma, double p)	Create a Gaussian mutation operator.
static <T extends RealValued> GaussianMutation<T>	createGaussianMutation(double sigma, double lowerBound, double upperBound)	Creates a Gaussian mutation operator, such that the mutate method constrains each mutated real value to lie in the interval [lowerBound, upperBound].
static <T extends RealValued> GaussianMutation<T>	createGaussianMutation(double sigma, int k)	Create a Gaussian mutation operator.
final double	get(int i)	Accesses the current value of the mutation parameter.
final int	length()	Gets the number of parameters.
void	mutate(T c)	Mutates a candidate solution to a problem, by randomly modifying its state.
final void	set(double[] values)	Sets the mutation parameter to a specified value.
final void	set(int i, double value)	Sets the mutation parameter to a specified value.
GaussianMutation<T>	split()	Generates a functionally identical copy of this object, for use in multithreaded implementations of search algorithms.
final double[]	toArray(double[] values)	Accesses the current value of the mutation parameter as an array.

Methods inherited from class java.lang.Object

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

Method Details

createGaussianMutation

public static <T extends RealValued>
GaussianMutation<T> createGaussianMutation()

Creates a Gaussian mutation operator with standard deviation equal to 1.

Type Parameters:

T - The specific RealValued type.

Returns:

A Gaussian mutation operator.

createGaussianMutation

public static <T extends RealValued>
GaussianMutation<T> createGaussianMutation(double sigma)

Creates a Gaussian mutation operator.

Type Parameters:

T - The specific RealValued type.

Parameters:

sigma - The standard deviation of the Gaussian.

Returns:

A Gaussian mutation operator.

createGaussianMutation

public static <T extends RealValued>
GaussianMutation<T> createGaussianMutation(double sigma,
 double lowerBound,
 double upperBound)

Creates a Gaussian mutation operator, such that the mutate method constrains each mutated real value to lie in the interval [lowerBound, upperBound].

Type Parameters:

T - The specific RealValued type.

Parameters:

sigma - The standard deviation of the Gaussian.

lowerBound - A lower bound on the result of a mutation.

upperBound - An upper bound on the result of a mutation.

Returns:

A Gaussian mutation operator.

createGaussianMutation

public static <T extends RealValued>
GaussianMutation<T> createGaussianMutation(double sigma,
 int k)

Create a Gaussian mutation operator.

Type Parameters:

T - The specific RealValued type.

Parameters:

sigma - The standard deviation of the Gaussian mutation.

k - The number of input variables that the MutationOperator.mutate(T) method changes when called. The k input variables are chosen uniformly at random from among all subsets of size k. If there are less than k input variables, then all are mutated.

Returns:

A Gaussian mutation operator

Throws:

IllegalArgumentException - if k < 1

createGaussianMutation

public static <T extends RealValued>
GaussianMutation<T> createGaussianMutation(double sigma,
 double p)

Create a Gaussian mutation operator.

Type Parameters:

T - The specific RealValued type.

Parameters:

sigma - The standard deviation of the Gaussian mutation.

p - The probability that the MutationOperator.mutate(T) method changes an input variable. If there are n input variables, then n*p input variables will be mutated on average during a single call to the MutationOperator.mutate(T) method.

Returns:

A Gaussian mutation operator

Throws:

IllegalArgumentException - if p ≤ 0

split

public GaussianMutation<T> split()

Description copied from interface: Splittable

Generates a functionally identical copy of this object, for use in multithreaded implementations of search algorithms. The state of the object that is returned may or may not be identical to that of the original. Thus, this is a distinct concept from the functionality of the Copyable interface. Classes that implement this interface must ensure that the object returned performs the same functionality, and that it does not share any state data that would be either unsafe or inefficient for concurrent access by multiple threads. The split method is allowed to simply return the this reference, provided that it is both safe and efficient for multiple threads to share a single copy of the Splittable object. The intention is to provide a multithreaded search with the capability to provide spawned threads with their own distinct search operators. Such multithreaded algorithms can call the split method for each thread it spawns to generate a functionally identical copy of the operator, but with independent state.

Specified by:

split in interface Splittable<T extends RealValued>

Returns:

A functionally identical copy of the object, or a reference to this if it is both safe and efficient for multiple threads to share a single instance of this Splittable object.

copy

public GaussianMutation<T> copy()

Creates an identical copy of this object.

Specified by:

copy in interface Copyable<T extends RealValued>

Returns:

an identical copy of this object

mutate

public void mutate(T c)

Description copied from interface: MutationOperator

Mutates a candidate solution to a problem, by randomly modifying its state. The mutant that is produced is in the local neighborhood of the original candidate solution.

Specified by:

mutate in interface MutationOperator<T extends RealValued>

Parameters:

c - The candidate solution subject to the mutation. This method changes the state of c.

length

public final int length()

Description copied from interface: RealValued

Gets the number of parameters.

Specified by:

length in interface RealValued

Returns:

The number of parameters for this function.

get

public final double get(int i)

Accesses the current value of the mutation parameter.

Specified by:

get in interface RealValued

Parameters:

i - Ignored.

Returns:

The current value of the mutation parameter.

toArray

public final double[] toArray(double[] values)

Accesses the current value of the mutation parameter as an array. This method implemented strictly to meet implementation requirements of RealValued interface.

Specified by:

toArray in interface RealValued

Parameters:

values - An array to hold the result. If values is null or if values.length is not equal 1, then a new array is constructed for the result.

Returns:

An array containing the current value of the mutation parameter.

set

public final void set(int i,
 double value)

Sets the mutation parameter to a specified value.

Specified by:

set in interface RealValued

Parameters:

i - Ignored.

value - The new value for the mutation parameter.

set

public final void set(double[] values)

Sets the mutation parameter to a specified value.

Specified by:

set in interface RealValued

Parameters:

values - The new value for the mutation parameter is in values[0], the rest is ignored.