org.uncommons.watchmaker.framework.selection
Class StochasticUniversalSampling

java.lang.Object
  org.uncommons.watchmaker.framework.selection.StochasticUniversalSampling

All Implemented Interfaces:

SelectionStrategy<Object>

public class StochasticUniversalSampling
extends Object
implements SelectionStrategy<Object>

An alternative to RouletteWheelSelection as a fitness-proportionate selection strategy. Ensures that the frequency of selection for each candidate is consistent with its expected frequency of selection.

Author:

Daniel Dyer

Constructor Summary

StochasticUniversalSampling()

Method Summary

<S> List<S>	select(List<EvaluatedCandidate<S>> population, boolean naturalFitnessScores, int selectionSize, Random rng) Select the specified number of candidates from the population.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

StochasticUniversalSampling

public StochasticUniversalSampling()

Method Detail

select

public <S> List<S> select(List<EvaluatedCandidate<S>> population,
                          boolean naturalFitnessScores,
                          int selectionSize,
                          Random rng)

Description copied from interface: SelectionStrategy

Select the specified number of candidates from the population. Implementations may assume that the population is sorted in descending order according to fitness (so the fittest individual is the first item in the list).

It is an error to call this method with an empty or null population.

Specified by:

select in interface SelectionStrategy<Object>

Type Parameters:

S - The type of evolved entity that we are selecting, a sub-type of T.

Parameters:

population - The population from which to select.

naturalFitnessScores - Whether higher fitness values represent fitter individuals or not.

selectionSize - The number of individual selections to make (not necessarily the number of distinct candidates to select, since the same individual may potentially be selected more than once).

rng - Source of randomness for stochastic selection strategies.

Returns:

A list containing the selected candidates. Some individual canidates may potentially have been selected multiple times.

toString

public String toString()

Overrides:

toString in class Object