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

Class CycleMutation

java.lang.Object
org.cicirello.search.operators.permutations.CycleMutation
All Implemented Interfaces:
Splittable<MutationOperator<Permutation>>, MutationOperator<Permutation>, UndoableMutationOperator<Permutation>
public final class CycleMutation extends Object implements UndoableMutationOperator<Permutation>
This class implements the Cycle(kmax) form of cycle mutation on permutations, where one mutation generates a random permutation cycle. Given the original parent permutation and its mutant, a permutation cycle can be defined as follows. Imagine a graph with n vertexes, where n is the permutation length. Now consider that for each index i, we define an edge in that graph between vertex parent[i] and vertex mutant[i]. A permutation cycle consists of all of the elements from one of the cycles in that graph. The length of a cycle is the number of elements in it. Consider an example permutation, p1 = [0, 1, 2, 3, 4], and another permutation, p2 = [0, 3, 2, 1, 4]. This pair of permutations has a 2-cycle (i.e., a cycle of length 2) consisting of elements 1 and 3. Consider a second example, p1 = [0, 1, 2, 3, 4], and p2 = [0, 4, 2, 1, 3]. This example has a 3-cycle consisting of elements 1, 3, and 4. Notice that position 1 has elements 1 and 4, position 4 has elements 4 and 3, and position 3 has elements 3 and 1, so in the hypothetical graph described above, there would be an edges from 1 to 4, 4 to 3, and 3 to 1, a cycle of length 3.

The Cycle(kmax) version of cycle mutation chooses the cycle size k uniformly at random from [2, kmax], and then creates a random k-element cycle. The kmax is a parameter allowing the evolutionary algorithm implementer the ability to control the allowed range of cycle sizes. The combination of k elements is chosen uniformly at random from all possible combinations of k elements. Note that a 2-cycle is simply a swap.

The runtime of the mutate method is O(min(n, kmax2)), and derives from the combination of algorithms utilized by the EnhancedSplittableGenerator class in sampling k random integers. For small values of kmax, the runtime is essentially constant. The runtime of the undo method is O(kmax).

Cycle mutation in both of its forms, including Cycle(kmax), was introduced in the following article:

Vincent A. Cicirello. 2022. Cycle Mutation: Evolving Permutations via Cycle Induction, Applied Sciences, 12(11), Article 5506 (June 2022). doi:10.3390/app12115506. [PDF] [BIB] [arXiv]

  • Constructor Summary

    Constructors
    Constructor
    Description
    CycleMutation(int kmax)
    Constructs an CycleMutation mutation operator.

  • Method Summary

    Modifier and Type
    Method
    Description
    final void
    mutate(Permutation c)
    Mutates a candidate solution to a problem, by randomly modifying its state.
    CycleMutation
    split()
    Generates a functionally identical copy of this object, for use in multithreaded implementations of search algorithms.
    final void
    undo(Permutation 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

    • CycleMutation

      public CycleMutation(int kmax)
      Constructs an CycleMutation mutation operator.
      Parameters:
      kmax - The maximum length cycle to generate, which must be at least 2.
      Throws:
      IllegalArgumentException - if kmax < 2.

  • 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 CycleMutation 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.