Class CauchyMutation<T extends RealValued>
 java.lang.Object

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

 Type Parameters:
T
 The specific RealValued type.
 All Implemented Interfaces:
Splittable<MutationOperator<T>>
,MutationOperator<T>
,RealValued
,Copyable<CauchyMutation<T>>
 Direct Known Subclasses:
UndoableCauchyMutation
public class CauchyMutation<T extends RealValued> extends Object implements MutationOperator<T>, RealValued, Copyable<CauchyMutation<T>>
This class implements Cauchy mutation. Cauchy mutation is for mutating floatingpoint 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 Cauchy mutation, a value v is mutated by adding a randomly generated m such that m is drawn from a Cauchy distribution with location parameter 0 (i.e., median 0) and scale parameter, scale. It is commonly employed in evolutionary computation when mutating real valued parameters. It is an alternative to the slightly more common Gaussian mutation (see the
GaussianMutation
class). Gaussian mutation has better convergence properties, however, due to the heavytailed nature of the Cauchy distribution, Cauchy mutation can sometimes escape local optima better than Gaussian mutation (i.e., Cauchy mutation is more likely than Gaussian mutation to make large jumps).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 CauchyMutation object to themutate(T)
method of a CauchyMutation object.To construct a CauchyMutation, you must use one of the factory methods. See the various
createCauchyMutation()
methods.Cauchy mutation was introduced in the following article:
H.H. Szu and R.L. Hartley. Nonconvex optimization by fast simulated annealing. Proceedings of the IEEE, 75(11): 1538–1540, November 1987.


Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description CauchyMutation<T>
copy()
Creates an identical copy of this object.static <T extends RealValued>
CauchyMutation<T>createCauchyMutation()
Creates a Cauchy mutation operator with scale parameter equal to 1.static <T extends RealValued>
CauchyMutation<T>createCauchyMutation(double scale)
Creates a Cauchy mutation operator.static <T extends RealValued>
CauchyMutation<T>createCauchyMutation(double scale, double p)
Create a Cauchy mutation operator.static <T extends RealValued>
CauchyMutation<T>createCauchyMutation(double scale, int k)
Create a Cauchy mutation operator.boolean
equals(Object other)
Indicates whether some other object is equal to this one.double
get(int i)
Accesses the current value of scale.int
hashCode()
Returns a hash code value for the object.int
length()
Gets the number of parameters.void
mutate(T c)
Mutates a candidate solution to a problem, by randomly modifying its state.void
set(int i, double value)
Sets scale to a specified value.CauchyMutation<T>
split()
Generates a functionally identical copy of this object, for use in multithreaded implementations of search algorithms.double[]
toArray(double[] values)
Accesses the current value of scale as an array.



Method Detail

createCauchyMutation
public static <T extends RealValued> CauchyMutation<T> createCauchyMutation()
Creates a Cauchy mutation operator with scale parameter equal to 1. Type Parameters:
T
 The specific RealValued type. Returns:
 A Cauchy mutation operator.

createCauchyMutation
public static <T extends RealValued> CauchyMutation<T> createCauchyMutation(double scale)
Creates a Cauchy mutation operator. Type Parameters:
T
 The specific RealValued type. Parameters:
scale
 The scale parameter of the Cauchy. Returns:
 A Cauchy mutation operator.

createCauchyMutation
public static <T extends RealValued> CauchyMutation<T> createCauchyMutation(double scale, int k)
Create a Cauchy mutation operator. Type Parameters:
T
 The specific RealValued type. Parameters:
scale
 The scale parameter of the Cauchy mutation.k
 The number of input variables that themutate(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 Cauchy mutation operator
 Throws:
IllegalArgumentException
 if k < 1

createCauchyMutation
public static <T extends RealValued> CauchyMutation<T> createCauchyMutation(double scale, double p)
Create a Cauchy mutation operator. Type Parameters:
T
 The specific RealValued type. Parameters:
scale
 The scale parameter of the Cauchy mutation.p
 The probability that themutate(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 themutate(T)
method. Returns:
 A Cauchy 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 interfaceMutationOperator<T extends RealValued>
 Parameters:
c
 The candidate solution subject to the mutation. This method changes the state of c.

split
public CauchyMutation<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 theCopyable
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 interfaceSplittable<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 CauchyMutation<T> copy()
Creates an identical copy of this object. Specified by:
copy
in interfaceCopyable<T extends RealValued>
 Returns:
 an identical copy of this 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.

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.

length
public final int length()
Description copied from interface:RealValued
Gets the number of parameters. Specified by:
length
in interfaceRealValued
 Returns:
 The number of parameters for this function.

get
public final double get(int i)
Accesses the current value of scale. Specified by:
get
in interfaceRealValued
 Parameters:
i
 Ignored. Returns:
 The current value of scale.

toArray
public final double[] toArray(double[] values)
Accesses the current value of scale as an array. This method implemented strictly to meet implementation requirements of RealValued interface. Specified by:
toArray
in interfaceRealValued
 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 scale.

set
public final void set(int i, double value)
Sets scale to a specified value. Specified by:
set
in interfaceRealValued
 Parameters:
i
 Ignored.value
 The new value for scale.

