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, SPEA2TournamentSelection

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

Version:

1.0

Author:

Sean Luke

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static String	P_PICKWORST
static String	P_SIZE size parameter
static String	P_TOURNAMENT default base
boolean	pickWorst Do we pick the worst instead of the best?
double	probabilityOfPickingSizePlusOne Probablity of picking the size plus one
(package private) int	size Base size of the tournament; this may change.

Fields inherited from class ec.SelectionMethod

INDS_PRODUCED

Fields inherited from class ec.BreedingSource

NO_PROBABILITY, P_PROB, probability

Constructor Summary

Constructors

Constructor and Description
TournamentSelection()

Method Summary

Methods

Modifier and Type	Method and Description
boolean	betterThan(Individual first, Individual second, int subpopulation, EvolutionState state, int thread) Returns true if *first* is a better (fitter, whatever) individual than *second*.
Parameter	defaultBase() Returns the default base for this prototype.
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.
int	getTournamentSizeToUse(MersenneTwisterFast random) Returns a tournament size to use, at random, based on base size and probability of picking the size plus one.
void	individualReplaced(SteadyStateEvolutionState state, int subpopulation, int thread, int individual) Called whenever an individual has been replaced by another in the population.
int	produce(int subpopulation, EvolutionState state, int thread) An alternative form of "produce" special to Selection Methods; selects an individual from the given subpopulation and returns its position in that subpopulation.
void	setup(EvolutionState state, Parameter base) Sets up the BreedingPipeline.
void	sourcesAreProperForm(SteadyStateEvolutionState state) 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.

Methods inherited from class ec.SelectionMethod

finishProducing, prepareToProduce, produce, produces, typicalIndsProduced

Methods inherited from class ec.BreedingSource

clone, getProbability, pickRandom, preparePipeline, setProbability, setupProbabilities

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

P_TOURNAMENT

public static final String P_TOURNAMENT

default base

See Also:

Constant Field Values

P_PICKWORST

public static final String P_PICKWORST

See Also:

Constant Field Values

P_SIZE

public static final String P_SIZE

size parameter

See Also:

Constant Field Values

size

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 Detail

TournamentSelection

public TournamentSelection()

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)

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. number 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