Package ec.select

Class SUSSelection

java.lang.Object
ec.BreedingSource
ec.SelectionMethod
ec.select.SUSSelection
All Implemented Interfaces:
Prototype, Setup, RandomChoiceChooserD, Serializable, 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:

  • Field Details

    • P_SUS

      public static final String P_SUS
      Default base
      See Also:

    • P_SHUFFLE

      public static final String P_SHUFFLE
      See Also:

    • 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 Details

    • SUSSelection

      public SUSSelection()

  • Method Details

    • 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:

    • 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