Module org.cicirello.chips_n_salsa
Package org.cicirello.search.operators.permutations

Class UndoableScrambleMutation

java.lang.Object
org.cicirello.search.operators.permutations.UndoableScrambleMutation
All Implemented Interfaces:
PermutationUnaryOperator, Splittable<MutationOperator<Permutation>>, MutationOperator<Permutation>, UndoableMutationOperator<Permutation>
public final class UndoableScrambleMutation extends Object implements UndoableMutationOperator<Permutation>, PermutationUnaryOperator
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(n-1)/2 possible pairs of indexes, where n is the length of the permutation.

The runtime (worst case and average case) of both the mutate and undo 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 the ScrambleMutation 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 Details

    • UndoableScrambleMutation

      public UndoableScrambleMutation()
      Constructs an UndoableScrambleMutation mutation operator.

  • Method Details

    • 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 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 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<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.

    • apply

      public void apply(int[] perm)
      See PermutationUnaryOperator for details of this method. This method is not intended for direct usage. Use the undo(org.cicirello.permutations.Permutation) method instead.
      Specified by:
      apply in interface PermutationUnaryOperator
      Parameters:
      perm - The raw representation of the permutation for undoing the most recent mutation.