ec.select

Class SUSSelection

java.lang.Object

ec.BreedingSource

ec.SelectionMethod

ec.select.SUSSelection

All Implemented Interfaces:

Prototype, Setup, RandomChoiceChooserD, java.io.Serializable, java.lang.Cloneable

public class SUSSelection
extends SelectionMethod

Picks individuals in a population using the Stochastic Universal Selection (SUS) process, using fitnesses as returned by their fitness() methods. This is expensive to set up and bring down, so it's not appropriate for steady-state evolution. If you're not familiar with the relative advantages of selection methods and just want a good one, use TournamentSelection instead. Not appropriate for multiobjective fitnesses.

By default this implementation of SUS shuffles the order of the individuals in the distribution before performing selection. This isn't always present in classic implementations of the algorithm but it can't hurt anything and certainly can avoid certain pathological situations. If you'd prefer not to preshuffle, set shuffle=false Note that we don't actually change the order of the individuals in the population -- instead we maintain our own internal array of indices and shuffle that.

Like truncation selection, SUS samples N individuals (with replacement) up front from the population, Then returns those individuals one by one. ECJ's implementation assumes that N is the size of the population -- that is, you're going to ultimately request a whole population out of this one selection method. This could be a false assumption: for example, if you only sometimes call this selection method, and sometimes TournamentSelection; or if you've got multiple pipelines. In these cases, SUS is probably a bad choice anyway.

If you ask for more than a population's worth of individuals, SUS tries to handle this gracefully by reshuffling its array and starting to select over again. But again that might suggest you are doing something wrong.

Note: Fitnesses must be non-negative. 0 is assumed to be the worst fitness.

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

Parameters

base.shuffle bool = true (default) or false

(should we preshuffle the array before doing selection?)

Default Base
select.sus

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
double[]	fitnesses The distribution of fitnesses.
int[]	indices An array of pointers to individuals in the population, shuffled along with the fitnesses array.
int	lastIndex The index in the array of the last individual selected.
double	offset The floating point value to consider for the next selected individual.
static java.lang.String	P_SHUFFLE
static java.lang.String	P_SUS Default base
boolean	shuffle Should we shuffle first?
int	steps How many samples have been done?

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
SUSSelection()

Method Summary

Modifier and Type	Method and Description
Parameter	defaultBase() Returns the default base for this prototype.
void	prepareToProduce(EvolutionState s, int subpopulation, int thread) A default version of prepareToProduce which does nothing.
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.

Methods inherited from class ec.SelectionMethod

finishProducing, produce, produces, typicalIndsProduced

Methods inherited from class ec.BreedingSource

clone, getProbability, pickRandom, preparePipeline, setProbability, setupProbabilities

Methods inherited from class java.lang.Object

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

Field Detail

P_SUS

public static final java.lang.String P_SUS

Default base

See Also:

Constant Field Values

P_SHUFFLE

public static final java.lang.String P_SHUFFLE

See Also:

Constant Field Values

indices

public int[] indices

An array of pointers to individuals in the population, shuffled along with the fitnesses array.

fitnesses

public double[] fitnesses

The distribution of fitnesses.

shuffle

public boolean shuffle

Should we shuffle first?

offset

public double offset

The floating point value to consider for the next selected individual.

lastIndex

public int lastIndex

The index in the array of the last individual selected.

steps

public int steps

How many samples have been done?

Constructor Detail

SUSSelection

public SUSSelection()

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(...).

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 s,
                             int subpopulation,
                             int thread)

Description copied from class: SelectionMethod

A default version of prepareToProduce which does nothing.

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