ec.parsimony
Class BucketTournamentSelection

java.lang.Object
  extended by ec.BreedingSource
      extended by ec.SelectionMethod
          extended by ec.parsimony.BucketTournamentSelection
All Implemented Interfaces:
Prototype, Setup, SteadyStateBSourceForm, RandomChoiceChooser, 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

Version:
1.0
Author:
Liviu Panait
See Also:
Serialized Form

Field Summary
static int DEFAULT_SIZE
          Default size
static int N_BUCKETS_DEFAULT
          Default number of buckets
static java.lang.String P_BUCKETS
          The number of buckets
static java.lang.String P_PICKWORST
          If the worst individual should be picked in the tournament
static java.lang.String P_SIZE
          Tournament size parameter
static java.lang.String P_TOURNAMENT
          Default base
 boolean pickWorst
          Do we pick the worst instead of the best?
 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
BucketTournamentSelection()
           
 
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.
 void prepareToProduce(EvolutionState state, int subpopulation, int thread)
          Prepare to produce: create the buckets!!!!
 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, preparePipeline, produce, 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
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

DEFAULT_SIZE

public static final int DEFAULT_SIZE
Default size

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)

prepareToProduce

public void prepareToProduce(EvolutionState state,
                             int subpopulation,
                             int thread)
Prepare to produce: create the buckets!!!!

Overrides:
prepareToProduce in class SelectionMethod

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