Package org.cicirello.search.operators.permutations

Class RotationMutation

java.lang.Object

org.cicirello.search.operators.permutations.RotationMutation

All Implemented Interfaces:

Splittable<MutationOperator<Permutation>>, IterableMutationOperator<Permutation>, MutationOperator<Permutation>, UndoableMutationOperator<Permutation>

public final class RotationMutation
extends Object
implements UndoableMutationOperator<Permutation>, IterableMutationOperator<Permutation>

This class implements a rotation mutation on permutations, where one mutation consists in a random circular rotation of the permutation. The number of positions to rotate the permutation is uniformly at random from among the n-1 possible rotations, where the length of the permutation is n. The runtime of both the mutate and undo methods is O(n).

Unlike the other mutation operators of the Chips-n-Salsa library, it is not possible to transform one permutation to any other simply via some sequence of mutations. Thus, RotationMutation is unlikely to be effective as the only mutation operator. The intention of the RotationMutation is for it to be used in combination with other mutation operators.

Constructor Summary

Constructors

Constructor	Description
RotationMutation()	Constructs an RotationMutation mutation operator.

Method Summary

Modifier and Type	Method	Description
MutationIterator	iterator(Permutation p)	Creates and returns a MutationIterator that can be used to systematically iterate over all of the direct neighbors (i.e., a single mutation step away) of a candidate solution, as one might do in a hill climber.
void	mutate(Permutation c)	Mutates a candidate solution to a problem, by randomly modifying its state.
RotationMutation	split()	Generates a functionally identical copy of this object, for use in multithreaded implementations of search algorithms.
void	undo(Permutation c)	Returns a candidate solution to its previous state prior to the most recent mutation performed.

Methods inherited from class java.lang.Object

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

Constructor Detail

RotationMutation

public RotationMutation()

Constructs an RotationMutation mutation operator.

Method Detail

mutate

public void mutate(Permutation 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<Permutation>

Parameters:

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

undo

public void undo(Permutation c)

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 interface UndoableMutationOperator<Permutation>

Parameters:

c - The candidate solution to revert.

split

public RotationMutation 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 IterableMutationOperator<Permutation>

Specified by:

split in interface Splittable<MutationOperator<Permutation>>

Specified by:

split in interface UndoableMutationOperator<Permutation>

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.

iterator

public MutationIterator iterator(Permutation p)

Creates and returns a MutationIterator that can be used to systematically iterate over all of the direct neighbors (i.e., a single mutation step away) of a candidate solution, as one might do in a hill climber.

The worst case runtime of the MutationIterator.nextMutant() and MutationIterator.rollback() methods of the MutationIterator created by this method is O(n). The runtime of the MutationIterator.hasNext() and MutationIterator.setSavepoint() methods is O(1).

Specified by:

iterator in interface IterableMutationOperator<Permutation>

Parameters:

p - The candidate solution subject to the mutation. Calling methods of the MutationIterator that is returned changes the state of that candidate solution. See the documentation of those methods for details of how such changes may occur.

Returns:

A MutationIterator for iterating over the direct neighbors of a candidate solution.