ec.select
Class TournamentSelection

java.lang.Object
  extended by ec.BreedingSource
      extended by ec.SelectionMethod
          extended by ec.select.TournamentSelection
All Implemented Interfaces:
Prototype, Setup, SteadyStateBSourceForm, RandomChoiceChooser, java.io.Serializable, java.lang.Cloneable
Direct Known Subclasses:
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 also be a floating-point value between 1.0 and 2.0, exclusive of them. In this situation, two individuals are chosen at random, and the better one is selected with a probability of size/2

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
int >= 1 or 1.0 < float < 2.0
(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
static int DEFAULT_SIZE
           
static java.lang.String P_PICKWORST
           
static java.lang.String P_SIZE
          size parameter
static java.lang.String P_TOURNAMENT
          default base
 boolean pickWorst
          Do we pick the worst instead of the best?
 double probabilityOfSelection
          What's our probability of selection? If 1.0, we always pick the "good" individual.
 int size
          Size of the tournament
 
Fields inherited from class ec.SelectionMethod
INDS_PRODUCED
 
Fields inherited from class ec.BreedingSource
CHECKBOUNDARY, DEFAULT_PRODUCED, NO_PROBABILITY, P_PROB, probability, UNUSED
 
Constructor Summary
TournamentSelection()
           
 
Method Summary
 Parameter defaultBase()
          Returns the default base for this prototype.
 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.
 int produce(int min, int max, int start, int subpopulation, Individual[] inds, EvolutionState state, int thread)
          Produces n individuals from the given subpopulation and puts them into inds[start...start+n-1], where n = Min(Max(q,min),max), where q is the "typical" number of individuals the BreedingSource produces in one shot, and returns n.
 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, preparePipeline, prepareToProduce, produces, typicalIndsProduced
 
Methods inherited from class ec.BreedingSource
clone, getProbability, pickRandom, 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 java.lang.String P_TOURNAMENT
default base

See Also:
Constant Field Values

P_PICKWORST

public static final java.lang.String P_PICKWORST
See Also:
Constant Field Values

P_SIZE

public static final java.lang.String P_SIZE
size parameter

See Also:
Constant Field Values

DEFAULT_SIZE

public static final int DEFAULT_SIZE
See Also:
Constant Field Values

size

public int size
Size of the tournament


probabilityOfSelection

public double probabilityOfSelection
What's our probability of selection? If 1.0, we always pick the "good" individual.


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)

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

produce

public int produce(int min,
                   int max,
                   int start,
                   int subpopulation,
                   Individual[] inds,
                   EvolutionState state,
                   int thread)
Description copied from class: BreedingSource
Produces n individuals from the given subpopulation and puts them into inds[start...start+n-1], where n = Min(Max(q,min),max), where q is the "typical" number of individuals the BreedingSource produces in one shot, and returns n. max must be >= min, and min must be >= 1. For example, crossover might typically produce two individuals, tournament selection might typically produce a single individual, etc.

Overrides:
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