Package org.cicirello.search.operators.permutations

Class BlockMoveMutation

  • All Implemented Interfaces:
    Splittable<MutationOperator<Permutation>>, IterableMutationOperator<Permutation>, MutationOperator<Permutation>, UndoableMutationOperator<Permutation>
    Direct Known Subclasses:
    WindowLimitedBlockMoveMutation
    public class BlockMoveMutation
extends Object
implements UndoableMutationOperator<Permutation>, IterableMutationOperator<Permutation>

    This class implements a block move mutation on permutations, where one mutation consists in removing a randomly chosen "block" (i.e., subsequence) and reinserting it at a different randomly chosen index. The block move is chosen uniformly at random from among all possible block moves.

    A block move is sometimes also called a block transposition, and can be described equivalently as swapping two adjacent blocks. Consider the permutation: p1 = [0, 1, 2, 3, 4, 5, 6, 7]. Now consider a block move that consists in removing block [4, 5, 6] and reinserting it at index 2. The result is p2 = [0, 1, 4, 5, 6, 2, 3, 7]. This can be described equivalently as swapping the two adjacent blocks [4, 5, 6] and [2, 3]. This mutation operator is related to the BlockInterchangeMutation, which swaps a pair of randomly selected non-overlapping blocks.

    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 removed block is at one end of the permutation, and reinserted at the opposite end, which causes all n permutation elements to move. On average, a block move affects n/2 element locations.

    • Constructor Detail

      • BlockMoveMutation

        public BlockMoveMutation()
        Constructs a BlockMoveMutation mutation operator.

    • 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 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 BlockMoveMutation 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 IterableMutationOperator<Permutation>
        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.