Class UndoableCauchyMutation<T extends RealValued>
 Type Parameters:
T
 The specific RealValued type.
 All Implemented Interfaces:
Splittable<MutationOperator<T>>
,MutationOperator<T>
,UndoableMutationOperator<T>
,RealValued
,Copyable<UndoableCauchyMutation<T>>
UndoableMutationOperator.undo(T)
method. 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 the MutationOperator.mutate(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
Modifier and TypeMethodDescriptioncopy()
Creates an identical copy of this object.static <T extends RealValued>
UndoableCauchyMutation<T>Creates a Cauchy mutation operator with scale parameter equal to 1 that supports the undo operation.static <T extends RealValued>
UndoableCauchyMutation<T>createCauchyMutation
(double scale) Creates a Cauchy mutation operator that supports the undo operation.static <T extends RealValued>
UndoableCauchyMutation<T>createCauchyMutation
(double scale, double p) Create a Cauchy mutation operator that supports the undo operation.static <T extends RealValued>
UndoableCauchyMutation<T>createCauchyMutation
(double scale, double lowerBound, double upperBound) Creates a Cauchy mutation operator that supports the undo operation, and such that the mutate method constrains each mutated real value to lie in the interval [lowerBound, upperBound].static <T extends RealValued>
UndoableCauchyMutation<T>createCauchyMutation
(double scale, int k) Create a Cauchy mutation operator that supports the undo operation.final double
get
(int i) Accesses the current value of the mutation parameter.final int
length()
Gets the number of parameters.final void
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.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.final void
Returns a candidate solution to its previous state prior to the most recent mutation performed.

Method Details

createCauchyMutation
Creates a Cauchy mutation operator with scale parameter equal to 1 that supports the undo operation. Type Parameters:
T
 The specific RealValued type. Returns:
 A Cauchy mutation operator.

createCauchyMutation
Creates a Cauchy mutation operator that supports the undo operation. 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> UndoableCauchyMutation<T> createCauchyMutation(double scale, double lowerBound, double upperBound) Creates a Cauchy mutation operator that supports the undo operation, and 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:
scale
 The scale parameter of the Cauchy.lowerBound
 A lower bound on the result of a mutation.upperBound
 An upper bound on the result of a mutation. Returns:
 A Cauchy mutation operator.

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

createCauchyMutation
public static <T extends RealValued> UndoableCauchyMutation<T> createCauchyMutation(double scale, double p) Create a Cauchy mutation operator that supports the undo operation. Type Parameters:
T
 The specific RealValued type. Parameters:
scale
 The scale parameter of the Cauchy mutation.p
 The probability that theMutationOperator.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 theMutationOperator.mutate(T)
method. Returns:
 A Cauchy mutation operator
 Throws:
IllegalArgumentException
 if p ≤ 0

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>
 Specified by:
split
in interfaceUndoableMutationOperator<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
Creates an identical copy of this object. Specified by:
copy
in interfaceCopyable<T extends RealValued>
 Returns:
 an identical copy of this object

mutate
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.

undo
Description copied from interface:UndoableMutationOperator
Returns a candidate solution to its previous state prior to the most recent mutation performed.For example, consider the following. Let c' be the current state of c. Let c'' be the state of c after mutate(c); If we then call undo(c), the state of c should revert back to c'.
The behavior of undo is undefined if c is altered by some other process between the calls to mutate and undo. The behavior is also undefined if a different candidate is given to undo then the last given to mutate. For example, if the following two statements are executed, mutate(c); undo(d);, the effect on d is undefined as it wasn't the most recently mutated candidate solution.
 Specified by:
undo
in interfaceUndoableMutationOperator<T extends RealValued>
 Parameters:
c
 The candidate solution to revert.

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 the mutation parameter. Specified by:
get
in interfaceRealValued
 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 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 the mutation parameter.

set
public final void set(int i, double value) Sets the mutation parameter to a specified value. Specified by:
set
in interfaceRealValued
 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 interfaceRealValued
 Parameters:
values
 The new value for the mutation parameter is in values[0], the rest is ignored.
