Package org.opt4j.optimizer.ea

Class Crowding

java.lang.Object
org.opt4j.optimizer.ea.Crowding
All Implemented Interfaces:
FrontDensityIndicator
public class Crowding extends Object implements FrontDensityIndicator
The Crowding calculates the crowding distance of Individuals as used for instance in the the Nsga2 algorithm. A bounding box around each individual is defined and restricted by the neighboring individuals in each dimension. The crowding distance is the sum of the side-lengths of the bounding box. If an individual does not have neighbors on all sides, the crowding distance is maximal. A normalization in each dimension is applied.
See Also:
  • "A fast and elitist multiobjective genetic algorithm : NSGA-II, K. Deb, A. Pratap, S. Agarwal, and T. Meyarivan Evolutionary Computation, IEEETransactions on, vol. 6, no. 2, pp. 182-197, August 2002."

  • Constructor Details

    • Crowding

      public Crowding()

  • Method Details

    • order

      public List<Individual> order(Map<Individual,Double> values)
      Returns an ordered list of the Individuals corresponding to their crowding distance. Individuals with a high crowding distance are sorted to the front.
      Parameters:
      values - the map of individuals to their crowding distance values
      Returns:
      the sorted list of individuals based on their crowding distance

    • getDensityValues

      public Map<Individual,Double> getDensityValues(Collection<Individual> individuals)
      Description copied from interface: FrontDensityIndicator
      Returns the density values for a collection on Individuals.
      Specified by:
      getDensityValues in interface FrontDensityIndicator
      Parameters:
      individuals - the individuals
      Returns:
      a map of each individual to its density value