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

Class BitFlipMutation

java.lang.Object
org.cicirello.search.operators.bits.BitFlipMutation
All Implemented Interfaces:
Splittable<MutationOperator<BitVector>>, MutationOperator<BitVector>, UndoableMutationOperator<BitVector>
public final class BitFlipMutation extends Object implements UndoableMutationOperator<BitVector>

This class implements Bit Flip Mutation, the mutation operator commonly used in genetic algorithms, but which can also be used with other metaheuristic search algorithms such as simulated annealing to generate random neighbors.

In a bit flip mutation, each bit of the BitVector is flipped with probability M, known as the mutation rate. Flipping a bit means changing it to 0 if it is currently a 1, or changing it to 1 if it is currently a 0. If the length of the BitVector is N, then the expected number of bits flipped during a single call to the mutate(org.cicirello.search.representations.BitVector) method is NM. However, there is no guarantee that any bits will be flipped by a call to the mutate(org.cicirello.search.representations.BitVector) method. This behavior is fine for genetic algorithms, but may be less than desirable for other metaheuristics, such as those that operate on a single candidate solution rather than a population of them. If you have need for a mutation operator for BitVectors that guarantees that all calls to the mutate(org.cicirello.search.representations.BitVector) method will change the BitVector, then consider using the DefiniteBitFlipMutation class instead.

  • Constructor Summary

    Constructors
    Constructor
    Description
    BitFlipMutation(double m)
    Constructs a BitFlipMutation operator with a specified mutation rate.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    mutate(BitVector c)
    Mutates a candidate solution to a problem, by randomly modifying its state.
    BitFlipMutation
    split()
    Generates a functionally identical copy of this object, for use in multithreaded implementations of search algorithms.
    void
    undo(BitVector c)
    Returns a candidate solution to its previous state prior to the most recent mutation performed.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • BitFlipMutation

      public BitFlipMutation(double m)
      Constructs a BitFlipMutation operator with a specified mutation rate.
      Parameters:
      m - The mutation rate, which is the probability of flipping any individual bit. The expected number of bits flipped during a call to the mutate(org.cicirello.search.representations.BitVector) method is m*N where N is the length of the mutated BitVector. There is no guarantee that any bits will be flipped during a mutation (e.g., if m is close to 0).
      Throws:
      IllegalArgumentException - if m ≤ 0 or if m ≥ 1.

  • Method Details

    • mutate

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

    • undo

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

    • split

      public BitFlipMutation 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<BitVector>>
      Specified by:
      split in interface UndoableMutationOperator<BitVector>
      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.