Class HeuristicSolutionGenerator<T extends Copyable<T>>

  • All Implemented Interfaces:
    Splittable<TrackableSearch<T>>, SimpleMetaheuristic<T>, TrackableSearch<T>
    Direct Known Subclasses:
    HeuristicPermutationGenerator

    public class HeuristicSolutionGenerator<T extends Copyable<T>>
    extends Object
    implements SimpleMetaheuristic<T>

    This class generates solutions to optimization problems using a constructive heuristic. Unless the heuristic given to it is randomized, this class is completely deterministic and has no randomized behavior. Thus, executing the optimize() method multiple times should produce the same result each time. When using a constructive heuristic, you begin with an empty solution, (e.g., an empty permutation for a permutation optimization problem), and you then use a constructive heuristic to choose which element to add to the partial solution. This is repeated until you derive a complete solution.

    • Constructor Detail

      • HeuristicSolutionGenerator

        public HeuristicSolutionGenerator​(ConstructiveHeuristic<T> heuristic)
        Constructs an HeuristicSolutionGenerator for generating solutions to an optimization problem using a constructive heuristic. A ProgressTracker is created for you.
        Parameters:
        heuristic - The constructive heuristic.
        Throws:
        NullPointerException - if heuristic is null
      • HeuristicSolutionGenerator

        public HeuristicSolutionGenerator​(ConstructiveHeuristic<T> heuristic,
                                          ProgressTracker<T> tracker)
        Constructs an HeuristicSolutionGenerator for generating solutions to an optimization problem using a constructive heuristic.
        Parameters:
        heuristic - The constructive heuristic.
        tracker - A ProgressTracker
        Throws:
        NullPointerException - if heuristic or tracker is null
    • Method Detail

      • optimize

        public final SolutionCostPair<T> optimize()
        Description copied from interface: SimpleMetaheuristic

        Executes a single run of a metaheuristic whose run length cannot be specified (e.g., a hill climber that terminates when it reaches a local optima, or a stochastic sampler that terminates when it constructs one solution, etc). If this method is called multiple times, each call is randomized in some algorithm dependent way (e.g., a hill climber begins at a new randomly generated starting solution), and reinitializes any control parameters that may have changed during the previous call to optimize to the start of run state.

        Specified by:
        optimize in interface SimpleMetaheuristic<T extends Copyable<T>>
        Returns:
        The current solution at the end of this run and its cost, which may or may not be the same as the solution contained in this metaheuristic's ProgressTracker, which contains the best of all runs. Returns null if the run did not execute, such as if the ProgressTracker already contains the theoretical best solution.
      • getProgressTracker

        public final ProgressTracker<T> getProgressTracker()
        Description copied from interface: TrackableSearch
        Gets the ProgressTracker object that is in use for tracking search progress. The object returned by this method contains the best solution found during the search (including across multiple concurrent runs if the search is multithreaded, or across multiple restarts if the run methods were called multiple times), as well as cost of that solution, among other information. See the ProgressTracker documentation for more information about the search data tracked by this object.
        Specified by:
        getProgressTracker in interface TrackableSearch<T extends Copyable<T>>
        Returns:
        the ProgressTracker in use by this metaheuristic.
      • setProgressTracker

        public final void setProgressTracker​(ProgressTracker<T> tracker)
        Description copied from interface: TrackableSearch
        Sets the ProgressTracker object that is in use for tracking search progress. Any previously set ProgressTracker is replaced by this one.
        Specified by:
        setProgressTracker in interface TrackableSearch<T extends Copyable<T>>
        Parameters:
        tracker - The new ProgressTracker to set. The tracker must not be null. This method does nothing if tracker is null.
      • getTotalRunLength

        public final long getTotalRunLength()
        Description copied from interface: TrackableSearch

        Gets the total run length of the metaheuristic. This is the total run length across all calls to the search. This may differ from what may be expected based on run lengths. For example, the search terminates if it finds the theoretical best solution, and also immediately returns if a prior call found the theoretical best. In such cases, the total run length may be less than the requested run length.

        The meaning of run length may vary from one metaheuristic to another. Therefore, implementing classes should provide fresh documentation rather than relying entirely on the interface documentation.

        Specified by:
        getTotalRunLength in interface TrackableSearch<T extends Copyable<T>>
        Returns:
        the total run length of the metaheuristic
      • split

        public HeuristicSolutionGenerator<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 SimpleMetaheuristic<T extends Copyable<T>>
        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.