Class UndoableScrambleMutation
 java.lang.Object

 org.cicirello.permutations.Permutation.Mechanic

 org.cicirello.search.operators.permutations.UndoableScrambleMutation

 All Implemented Interfaces:
Splittable<MutationOperator<Permutation>>
,MutationOperator<Permutation>
,UndoableMutationOperator<Permutation>
 Direct Known Subclasses:
WindowLimitedUndoableScrambleMutation
public class UndoableScrambleMutation extends Permutation.Mechanic implements UndoableMutationOperator<Permutation>
This class implements a scramble mutation on permutations, where one mutation consists in randomizing the order of a randomly selected subpermutation. This version of scramble mutation also supports the undo method. The pair of indexes that indicate the subpermutation to scramble is chosen uniformly at random from among all n(n1)/2 possible pairs of indexes, where n is the length of the permutation.
The runtime (worst case and average case) of both the
mutate
andundo
methods is O(n), where n is the length of the permutation. The worst case runtime occurs when the random indexes are the two end points. On average, a scramble mutation moves approximately n/3 elements.If you don't need the
undo
method, then it is recommended that you instead use theScrambleMutation
class instead to avoid the O(n) extra memory required to store the prior permutation state, as well as the time associated with copying that state prior to mutation.


Constructor Summary
Constructors Constructor Description UndoableScrambleMutation()
Constructs an UndoableScrambleMutation mutation operator.

Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
mutate(Permutation c)
Mutates a candidate solution to a problem, by randomly modifying its state.UndoableScrambleMutation
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 org.cicirello.permutations.Permutation.Mechanic
set, set, set




Method Detail

mutate
public final 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 interfaceMutationOperator<Permutation>
 Parameters:
c
 The candidate solution subject to the mutation. This method changes the state of c.

undo
public final 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 interfaceUndoableMutationOperator<Permutation>
 Parameters:
c
 The candidate solution to revert.

split
public UndoableScrambleMutation 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<MutationOperator<Permutation>>
 Specified by:
split
in interfaceUndoableMutationOperator<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.

