Package ec.select

Class TournamentSelection

java.lang.Object
ec.BreedingSource
ec.SelectionMethod
ec.select.TournamentSelection
All Implemented Interfaces:
Prototype, Setup, SteadyStateBSourceForm, RandomChoiceChooserD, Serializable, Cloneable
Direct Known Subclasses:
LexicographicTournamentSelection, ProportionalTournamentSelection, SpatialTournamentSelection
public class TournamentSelection extends SelectionMethod implements SteadyStateBSourceForm
Does a simple tournament selection, limited to the subpopulation it's working in at the time.

Tournament selection works like this: first, size individuals are chosen at random from the population. Then of those individuals, the one with the best fitness is selected.

size can be any floating point value >= 1.0. If it is a non- integer value x then either a tournament of size ceil(x) is used (with probability x - floor(x)), else a tournament of size floor(x) is used.

Common sizes for size include: 2, popular in Genetic Algorithms circles, and 7, popularized in Genetic Programming by John Koza. If the size is 1, then individuals are picked entirely at random.

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
double >= 1		 (the tournament size)
base.pick-worst
bool = true or false (default)		 (should we pick the worst individual in the tournament instead of the best?)

Default Base
select.tournament

See Also:

  • Field Details

    • P_TOURNAMENT

      public static final String P_TOURNAMENT
      default base
      See Also:

    • P_PICKWORST

      public static final String P_PICKWORST
      See Also:

    • P_SIZE

      public static final String P_SIZE
      size parameter
      See Also:

    • size

      public int size
      Base size of the tournament; this may change.

    • probabilityOfPickingSizePlusOne

      public double probabilityOfPickingSizePlusOne
      Probablity of picking the size plus one

    • pickWorst

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

  • Constructor Details

    • TournamentSelection

      public TournamentSelection()

  • Method Details

    • 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:

    • getTournamentSizeToUse

      public int getTournamentSizeToUse(MersenneTwisterFast random)
      Returns a tournament size to use, at random, based on base size and probability of picking the size plus one.

    • getRandomIndividual

      public int getRandomIndividual(int number, int subpopulation, EvolutionState state, int thread)
      Produces the index of a (typically uniformly distributed) randomly chosen individual to fill the tournament. numberinvalid input: '<'/> is the position of the individual in the tournament.

    • betterThan

      public boolean betterThan(Individual first, Individual second, int subpopulation, EvolutionState state, int thread)
      Returns true if *first* is a better (fitter, whatever) individual than *second*.

    • 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

    • individualReplaced

      public void individualReplaced(SteadyStateEvolutionState state, int subpopulation, int thread, int individual)
      Description copied from interface: SteadyStateBSourceForm
      Called whenever an individual has been replaced by another in the population.
      Specified by:
      individualReplaced in interface SteadyStateBSourceForm

    • sourcesAreProperForm

      public void sourcesAreProperForm(SteadyStateEvolutionState state)
      Description copied from interface: SteadyStateBSourceForm
      Issue an error (not a fatal -- we guarantee that callers of this method will also call exitIfErrors) if any of your sources, or their sources, etc., are not of SteadyStateBSourceForm.
      Specified by:
      sourcesAreProperForm in interface SteadyStateBSourceForm