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

Interface UndoableMutationOperator<T>

Type Parameters:
T - The type of object used to represent candidate solutions to the problem.
All Superinterfaces:
MutationOperator<T>, Splittable<MutationOperator<T>>
All Known Implementing Classes:
AdjacentSwapMutation, BitFlipMutation, BlockInterchangeMutation, BlockMoveMutation, CycleAlphaMutation, CycleMutation, DefiniteBitFlipMutation, HybridUndoableMutation, InsertionMutation, ReversalMutation, RotationMutation, SwapMutation, ThreeOptMutation, TwoChangeMutation, UndoableCauchyMutation, UndoableGaussianMutation, UndoableRandomValueChangeMutation, UndoableScrambleMutation, UndoableUniformMutation, UndoableUniformMutation, UndoableUniformScrambleMutation, WeightedHybridUndoableMutation, WindowLimitedBlockMoveMutation, WindowLimitedInsertionMutation, WindowLimitedReversalMutation, WindowLimitedSwapMutation, WindowLimitedUndoableScrambleMutation
public interface UndoableMutationOperator<T> extends MutationOperator<T>
Implement the UndoableMutationOperator interface to implement a mutation operator for use in simulated annealing, and other metaheuristics, that require a way to generate random neighbors of a candidate solution, and which supports an undo method.

The purpose of this subinterface is to enable efficient implementation of metaheuristics such as simulated annealing, which iteratively generate random neighbors moving to some and not moving to others. When the search chooses not to keep a neighbor, it needs an efficient way to return to the previous state. Without an undo method, it would need to save a copy of the original. Generating a copy of a candidate solution c is likely an operation whose cost is linear in the size of c, while in many cases it may be possible to implement undo in constant time.

If your mutation operator is one in which the inverse operation (i.e., the operation that reverts an object to its previous state from prior to the mutation) can be implemented without substantially affecting the runtime of the mutation itself, then implement the UndoableMutationOperator interface.

On the other hand, if implementing undo(T) would require significant added cost in either time or memory to the MutationOperator.mutate(T) method, then consider implementing two versions of your mutation operator, one that implements MutationOperator and a second that implements UndoableMutationOperator. In this way, you can use the first version with metaheuristics that do not utilize the undo method, and the second for those that do.

  • Method Summary

    Modifier and Type
    Method
    Description
    UndoableMutationOperator<T>
    split()
    Generates a functionally identical copy of this object, for use in multithreaded implementations of search algorithms.
    void
    undo(T c)
    Returns a candidate solution to its previous state prior to the most recent mutation performed.

    Methods inherited from interface org.cicirello.search.operators.MutationOperator

    mutate

  • Method Details

    • undo

      void undo(T c)
      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.

      Parameters:
      c - The candidate solution to revert.

    • split

      UndoableMutationOperator<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>
      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.