Class RandomSelection

  • All Implemented Interfaces:
    Splittable<SelectionOperator>, SelectionOperator

    public final class RandomSelection
    extends Object
    implements SelectionOperator

    This class implements a simple random selection operator that selects members of the population uniformly at random, independent of fitness values.

    This selection operator is compatible with all fitness functions, even in the case of negative fitness values, since it doesn't use the fitness values and simply picks randomly.

    The runtime to select M population members from a population of size N is O(M), which includes generating O(M) random int values.

    • Constructor Detail

      • RandomSelection

        public RandomSelection()
        Constructs the random selection operator.
    • Method Detail

      • select

        public void select​(PopulationFitnessVector.Integer fitnesses,
                           int[] selected)
        Description copied from interface: SelectionOperator
        Selects a set of members of the population based on fitness. Implementations should ensure that the array of indexes of population members is in a random order. For some selection operators, this required behavior is met by definition (e.g., the common fitness proportionate selection will have this behavior as is). But other selection operators may require randomizing the array of indexes after selection. For example, the obvious implementation of stochastic universal sampling will likely have all copies of an individual population member ordered together, and thus will require a shuffling of the array before returning.
        Specified by:
        select in interface SelectionOperator
        Parameters:
        fitnesses - A vector of fitnesses of the members of the population.
        selected - An array for the result. The selection operator should select selected.length members of the population based on fitnesses, populating selected with the indexes of the chosen members. Note that selected.length may be different than the fitnesses.size().
      • select

        public void select​(PopulationFitnessVector.Double fitnesses,
                           int[] selected)
        Description copied from interface: SelectionOperator
        Selects a set of members of the population based on fitness. Implementations should ensure that the array of indexes of population members is in a random order. For some selection operators, this required behavior is met by definition (e.g., the common fitness proportionate selection will have this behavior as is). But other selection operators may require randomizing the array of indexes after selection. For example, the obvious implementation of stochastic universal sampling will likely have all copies of an individual population member ordered together, and thus will require a shuffling of the array before returning.
        Specified by:
        select in interface SelectionOperator
        Parameters:
        fitnesses - A vector of fitnesses of the members of the population.
        selected - An array for the result. The selection operator should select selected.length members of the population based on fitnesses, populating selected with the indexes of the chosen members. Note that selected.length may be different than the fitnesses.size().
      • split

        public RandomSelection 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<SelectionOperator>
        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.