Module org.cicirello.chips_n_salsa
Package org.cicirello.search.ss

Interface ConstructiveHeuristic<T extends Copyable<T>>

Type Parameters:
T - The type of Partial object for which this ConstructiveHeuristic guides construction, which is assumed to be an object that is a sequence of integers (e.g., vector of integers, permutation, or some other indexable type that stores integers).
All Superinterfaces:
Splittable<ConstructiveHeuristic<T>>
All Known Implementing Classes:
ApparentTardinessCost, ApparentTardinessCostSetupAdjusted, ATCS, DynamicATCS, EarliestDueDate, ExponentialEarlyTardyHeuristic, HybridConstructiveHeuristic, LinearEarlyTardyHeuristic, MinimumSlackTime, Montagne, NearestCityHeuristic, NearestCityPairHeuristic, ShortestProcessingPlusSetupTime, ShortestProcessingPlusSetupTimePrecompute, ShortestProcessingTime, SmallestNormalizedSetup, SmallestSetup, SmallestSetupPrecompute, SmallestTwoJobSetup, WeightedCostOverTime, WeightedCostOverTimeSetupAdjusted, WeightedCriticalRatio, WeightedCriticalRatioSetupAdjusted, WeightedLongestProcessingTime, WeightedShortestProcessingPlusSetupTime, WeightedShortestProcessingPlusSetupTimeLateOnly, WeightedShortestProcessingPlusSetupTimePrecompute, WeightedShortestProcessingTime, WeightedShortestProcessingTimeLateOnly
public interface ConstructiveHeuristic<T extends Copyable<T>> extends Splittable<ConstructiveHeuristic<T>>
Classes implementing this interface are used as constructive heuristics for constructing heuristic solutions to optimization problems, as well as for certain stochastic sampling search algorithms.

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    completeLength()
    Gets the required length of complete solutions to the problem instance for which this constructive heuristic is configured.
    default IncrementalEvaluation<T>
    createIncrementalEvaluation()
    Creates an IncrementalEvaluation object corresponding to an initially empty Partial for use in incrementally constructing a solution to the problem for which this heuristic is designed.
    Partial<T>
    createPartial(int n)
    Creates an empty Partial solution, which will be incrementally transformed into a complete solution of a specified length.
    Problem<T>
    getProblem()
    Gets a reference to the instance of the optimization problem that is the subject of this heuristic.
    double
    h(Partial<T> p, int element, IncrementalEvaluation<T> incEval)
    Heuristically evaluates the possible addition of an element to the end of a Partial.
    default ConstructiveHeuristic<T>
    split()
    Generates a functionally identical copy of this object, for use in multithreaded implementations of search algorithms.

  • Method Details

    • h

      double h(Partial<T> p, int element, IncrementalEvaluation<T> incEval)
      Heuristically evaluates the possible addition of an element to the end of a Partial. Higher evaluations imply that the element is a better choice for the next element to add. For example, if you evaluate two elements, x and y, with h, and h returns a higher value for y than for x, then this means that y is believed to be the better choice according to the heuristic. Implementations of this interface must ensure that h always returns a positive result. This is because stochastic sampling algorithms such as HBSS and VBSS assume that the constructive heuristic returns only positive values.
      Parameters:
      p - The current state of the Partial
      element - The element under consideration for adding to the Partial
      incEval - An IncrementalEvaluation of p. This method assumes that incEval is of the same runtime type as the object returned by createIncrementalEvaluation().
      Returns:
      The heuristic evaluation of the hypothetical addition of element to the end of p. The higher the evaluation, the more important the heuristic believes that element should be added next. The intention is to compare the value returned with the heuristic evaluations of other elements. Individual results in isolation are not necessarily meaningful.
      Throws:
      ClassCastException - if incEval is not of the same runtime type as the objects returned by the createIncrementalEvaluation() method of the class implementing this interface

    • createIncrementalEvaluation

      default IncrementalEvaluation<T> createIncrementalEvaluation()
      Creates an IncrementalEvaluation object corresponding to an initially empty Partial for use in incrementally constructing a solution to the problem for which this heuristic is designed. The object returned incrementally computes any data associated with a Partial as needed by the h(org.cicirello.search.ss.Partial<T>, int, org.cicirello.search.ss.IncrementalEvaluation<T>) method. The h(org.cicirello.search.ss.Partial<T>, int, org.cicirello.search.ss.IncrementalEvaluation<T>) method will assume that it will be given an object of the specific runtime type returned by this method. It is unsafe to pass IncrementalEvaluation objects created by one heuristic to the h(org.cicirello.search.ss.Partial<T>, int, org.cicirello.search.ss.IncrementalEvaluation<T>) method of another.

      The default implementation simply returns null, which is appropriate for heuristics that won't benefit from incrementally computing heuristic information.

      Returns:
      An IncrementalEvaluation for an empty Partial to be used for incrementally computing any data required by the h(org.cicirello.search.ss.Partial<T>, int, org.cicirello.search.ss.IncrementalEvaluation<T>) method.

    • createPartial

      Partial<T> createPartial(int n)
      Creates an empty Partial solution, which will be incrementally transformed into a complete solution of a specified length.
      Parameters:
      n - the desired length of the final complete solution.
      Returns:
      an empty Partial solution

    • completeLength

      int completeLength()
      Gets the required length of complete solutions to the problem instance for which this constructive heuristic is configured.
      Returns:
      length of solutions to the problem instance for which this heuristic is configured

    • getProblem

      Problem<T> getProblem()
      Gets a reference to the instance of the optimization problem that is the subject of this heuristic.
      Returns:
      the instance of the optimization problem that is the subject of this heuristic.

    • split

      default ConstructiveHeuristic<T> split()
      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.

      The default implementation simply returns this, which is appropriate in all cases where an instance of the heuristic can be safely shared by multiple threads.

      Specified by:
      split in interface Splittable<T extends Copyable<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.