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

Class UndoableUniformScrambleMutation

java.lang.Object
org.cicirello.search.operators.permutations.UndoableUniformScrambleMutation
All Implemented Interfaces:
PermutationUnaryOperator, Splittable<MutationOperator<Permutation>>, MutationOperator<Permutation>, UndoableMutationOperator<Permutation>
public final class UndoableUniformScrambleMutation extends Object implements UndoableMutationOperator<Permutation>, PermutationUnaryOperator
This class implements a scramble mutation on permutations, where one mutation consists in randomizing the order of a non-contiguous subset of the permutation elements. It is controlled by a parameter U, which is the probability that an element is included in the scramble. On average, you can expect U*n elements to be randomized, where n is the length of the permutation. This version of uniform scramble mutation also supports the undo method.

The worst case and average case runtime of the mutate method is O(n), where n is the length of the permutation. The worst case runtime of the undo method is also O(n), but its average runtime is O(U*n).

If you don't need the undo method, then it is recommended that you instead use the UniformScrambleMutation 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

    • UndoableUniformScrambleMutation

      public UndoableUniformScrambleMutation(double u)
      Constructs a UndoableUniformScrambleMutation mutation operator.
      Parameters:
      u - The probability that an element is included in a scramble. If the permutation length is n, you can expect approximately u*n elements on average to be scrambled.
      Throws:
      IllegalArgumentException - if u is negative or if u is greater than 1.0.

    • UndoableUniformScrambleMutation

      public UndoableUniformScrambleMutation(double u, boolean guaranteeChange)
      Constructs a UndoableUniformScrambleMutation mutation operator.
      Parameters:
      u - The probability that an element is included in a scramble. If the permutation length is n, you can expect approximately u*n elements on average to be scrambled.
      guaranteeChange - If true, then the mutate method will be guaranteed to change the locations of at least 2 elements. Otherwise, if false, it may be possible (e.g., for low values of u) for the mutate method not to change anything during some calls.
      Throws:
      IllegalArgumentException - if u is negative or if u is greater than 1.0.

  • Method Details

    • 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 interface MutationOperator<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 interface UndoableMutationOperator<Permutation>
      Parameters:
      c - The candidate solution to revert.

    • split

      public UndoableUniformScrambleMutation 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 final 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.