Documentation of 'ec.parsimony.BucketTournamentSelection' Java class
BucketTournamentSelection
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ec.parsimony

Class BucketTournamentSelection

  • All Implemented Interfaces:
    Prototype, Setup, SteadyStateBSourceForm, RandomChoiceChooserD, java.io.Serializable, java.lang.Cloneable

    public class BucketTournamentSelection
extends SelectionMethod
implements SteadyStateBSourceForm
    Does a tournament selection, limited to the subpopulation it's working in at the time.

    Bucket Lexicographic Tournament selection works like as follows. There is a number of buckets (num-buckets) specified beforehand, and each is assigned a rank from 1 to num-buckets. The population, of size pop-size, is sorted by fitness. The bottom pop-size/num-buckets individuals are placed in the worst ranked bucket, plus any individuals remaining in the population with the same fitness as the best individual in the bucket. Then the second worst pop-size/num-buckets individuals are placed in the second worst ranked bucket, plus any individuals in the population equal in fitness to the best individual in that bucket. This continues until there are no individuals in the population. Note that the topmost bucket with individuals can hold fewer than pop-size/num-buckets individuals, if pop-size is not a multiple of num-buckets. Depending on the number of equal-fitness individuals in the population, there can be some top buckets that are never filled. The fitness of each individual in a bucket is set to the rank of the bucket holding it. Direct bucketing has the effect of trading off fitness differences for size. Thus the larger the bucket, the stronger the emphasis on size as a secondary objective. After ranking the individuals, size individuals are chosen at random from the population. Of those individuals, the one with the highest rank is selected. If the two individuals are in the same rank, meaning that they have similar fitness, the one with the smallest size is selected.

    Bucket Lexicographic Tournament selection is so simple that it doesn't need to maintain a cache of any form, so many of the SelectionMethod methods just don't do anything at all.

    Typical Number of Individuals Produced Per produce(...) call
    Always 1.

    Parameters

    base.size
    int >= 1 (default 7)    		 (the tournament size)
    base.pick-worst
    bool = true or false (default)    		 (should we pick the worst individual in the tournament instead of the best?)
    base.num-buckets
    int >= 1 (default 10)    		 (the number of buckets)

    Default Base
    select.bucket-tournament

    See Also:
    Serialized Form

    • Field Detail

      • P_TOURNAMENT

        public static final java.lang.String P_TOURNAMENT
        Default base
        See Also:
        Constant Field Values

      • P_PICKWORST

        public static final java.lang.String P_PICKWORST
        If the worst individual should be picked in the tournament
        See Also:
        Constant Field Values

      • P_SIZE

        public static final java.lang.String P_SIZE
        Tournament size parameter
        See Also:
        Constant Field Values

      • P_BUCKETS

        public static final java.lang.String P_BUCKETS
        The number of buckets
        See Also:
        Constant Field Values

      • N_BUCKETS_DEFAULT

        public static final int N_BUCKETS_DEFAULT
        Default number of buckets
        See Also:
        Constant Field Values

      • size

        public int size
        Size of the tournament

      • pickWorst

        public boolean pickWorst
        Do we pick the worst instead of the best?

    • Constructor Detail

      • BucketTournamentSelection

        public BucketTournamentSelection()

    • Method Detail

      • defaultBase

        public Parameter defaultBase()
        Description copied from interface: Prototype
        Returns the default base for this prototype. This should generally be implemented by building off of the static base() method on the DefaultsForm object for the prototype's package. This should be callable during setup(...).
        Specified by:
        defaultBase in interface Prototype

      • setup

        public void setup(EvolutionState state,
                  Parameter base)
        Description copied from class: BreedingSource
        Sets up the BreedingPipeline. You can use state.output.error here because the top-level caller promises to call exitIfErrors() after calling setup. Note that probability might get modified again by an external source if it doesn't normalize right.

        The most common modification is to normalize it with some other set of probabilities, then set all of them up in increasing summation; this allows the use of the fast static BreedingSource-picking utility method, BreedingSource.pickRandom(...). In order to use this method, for example, if four breeding source probabilities are {0.3, 0.2, 0.1, 0.4}, then they should get normalized and summed by the outside owners as: {0.3, 0.5, 0.6, 1.0}.

        Specified by:
        setup in interface Prototype
        Specified by:
        setup in interface Setup
        Overrides:
        setup in class BreedingSource
        See Also:
        Prototype.setup(EvolutionState,Parameter)

      • produce

        public int produce(int subpopulation,
                   EvolutionState state,
                   int thread)
        Description copied from class: SelectionMethod
        An alternative form of "produce" special to Selection Methods; selects an individual from the given subpopulation and returns its position in that subpopulation.
        Specified by:
        produce in class SelectionMethod
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