Module io.jenetics.base
Package io.jenetics

Class LinearRankSelector<G extends Gene<?,G>,C extends Comparable<? super C>>

java.lang.Object
io.jenetics.ProbabilitySelector<G,C>
io.jenetics.LinearRankSelector<G,C>
All Implemented Interfaces:
Selector<G,C>
public final class LinearRankSelector<G extends Gene<?,G>,C extends Comparable<? super C>> extends ProbabilitySelector<G,C>

In linear-ranking selection the individuals are sorted according to their fitness values. The rank N is assignee to the best individual and the rank 1 to the worst individual. The selection probability P(i) of individual i is linearly assigned to the individuals according to their rank.

P(i)=\frac{1}{N}\left(n^{-}+\left(n^{+}-n^{-}\right)\frac{i-1}{N-1}\right)

Here n-/N is the probability of the worst individual to be selected and n+/N the probability of the best individual to be selected. As the population size is held constant, the conditions n+ = 2 - n- and n- >= 0 must be fulfilled. Note that all individuals get a different rank, i.e., a different selection probability, even if the have the same fitness value.

T. Blickle, L. Thiele, A comparison of selection schemes used in evolutionary algorithms, Technical Report, ETH Zurich, 1997, page 37. http://citeseer.ist.psu.edu/blickle97comparison.html

Since:
1.0
Version:
5.0

  • Constructor Details

    • LinearRankSelector

      public LinearRankSelector(double nminus)
      Create a new LinearRankSelector with the given values for nminus.
      Parameters:
      nminus - nminus/N is the probability of the worst phenotype to be selected.
      Throws:
      IllegalArgumentException - if nminus < 0.

    • LinearRankSelector

      public LinearRankSelector()
      Create a new LinearRankSelector with nminus := 0.5.

  • Method Details

    • probabilities

      protected double[] probabilities(Seq<Phenotype<G,C>> population, int count)
      This method sorts the population in descending order while calculating the selection probabilities.
      Specified by:
      probabilities in class ProbabilitySelector<G extends Gene<?,G>,C extends Comparable<? super C>>
      Parameters:
      population - The unsorted population.
      count - The number of phenotypes to select. This parameter is not needed for most implementations.
      Returns:
      Probability array. The returned probability array must have the length population.size() and must sum to one. The returned value is checked with assert(Math.abs(math.sum(probabilities) - 1.0) < 0.0001) in the base class.

    • toString

      public String toString()
      Overrides:
      toString in class Object