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

Class WeightedHybridUndoableMutation<T>

java.lang.Object
org.cicirello.search.operators.WeightedHybridUndoableMutation<T>
Type Parameters:
T - The type of object used to represent candidate solutions to the problem.
All Implemented Interfaces:
Splittable<MutationOperator<T>>, MutationOperator<T>, UndoableMutationOperator<T>
public final class WeightedHybridUndoableMutation<T> extends Object implements UndoableMutationOperator<T>
A WeightedHybridMutation enables using multiple mutation operators for the search, such that each time the mutate(T) method is called, a randomly chosen mutation operator is applied to the candidate solution. The random choice of mutation operator is weighted proportionately based on an array of weights passed upon construction. This implementation supports the undo(T) method.

Consider the following weights: w = [ 1, 2, 3]. In this example, the first mutation operator will be used with probability 0.167, the second mutation operator will be used with probability 2/6 = 0.333, and the third mutation operator will be used with probability 3/6 = 0.5.

  • Constructor Details

    • WeightedHybridUndoableMutation

      public WeightedHybridUndoableMutation(Collection<? extends UndoableMutationOperator<T>> mutationOps, int[] weights)
      Constructs a WeightedHybridUndoableMutation from a Collection of UndoableMutationOperator.
      Parameters:
      mutationOps - A Collection of UndoableMutationOperator.
      weights - The array of weights, whose length must be equal to mutationOps.size(). Every element of weights must be greater than 0.
      Throws:
      IllegalArgumentException - if mutationOps doesn't contain any UndoableMutationOperator.
      IllegalArgumentException - if mutationOps.size() is not equal to weights.length.
      IllegalArgumentException - if any weights are non-positive.

  • Method Details

    • mutate

      public void mutate(T 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<T>
      Parameters:
      c - The candidate solution subject to the mutation. This method changes the state of c.

    • undo

      public void undo(T 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<T>
      Parameters:
      c - The candidate solution to revert.

    • split

      public WeightedHybridUndoableMutation<T> 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<T>
      Specified by:
      split in interface UndoableMutationOperator<T>
      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.