Class GaussianMutation<T extends RealValued>

  • Type Parameters:
    T - The specific RealValued type.
    All Implemented Interfaces:
    Splittable<MutationOperator<T>>, MutationOperator<T>, RealValued, Copyable<GaussianMutation<T>>
    Direct Known Subclasses:
    UndoableGaussianMutation

    public class GaussianMutation<T extends RealValued>
    extends Object
    implements MutationOperator<T>, RealValued, 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 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 Detail

      • createGaussianMutation

        public static <T extends RealValuedGaussianMutation<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 RealValuedGaussianMutation<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 RealValuedGaussianMutation<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 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 RealValuedGaussianMutation<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 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 mutate(T) method.
        Returns:
        A Gaussian mutation operator
        Throws:
        IllegalArgumentException - if p ≤ 0
      • 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.
      • 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.
      • equals

        public boolean equals​(Object other)
        Indicates whether some other object is equal to this one. The objects are equal if they are the same type of operator with the same parameters.
        Overrides:
        equals in class Object
        Parameters:
        other - the object with which to compare
        Returns:
        true if and only if the objects are equal
      • hashCode

        public int hashCode()
        Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.
        Overrides:
        hashCode in class Object
        Returns:
        a hash code value for this object
      • 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 sigma.
        Specified by:
        get in interface RealValued
        Parameters:
        i - Ignored.
        Returns:
        The current value of sigma.
      • toArray

        public final double[] toArray​(double[] values)
        Accesses the current value of sigma 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 sigma.
      • set

        public final void set​(int i,
                              double value)
        Sets sigma to a specified value.
        Specified by:
        set in interface RealValued
        Parameters:
        i - Ignored.
        value - The new value for sigma.