crowding

crowding.rb

def calculate_crowding_distance(pop)
  pop.each {|p| p[:dist] = 0.0}
  num_obs = pop.first[:objectives].size
  num_obs.times do |i|
    min = pop.min{|x,y| x[:objectives][i]<=>y[:objectives][i]}
    max = pop.max{|x,y| x[:objectives][i]<=>y[:objectives][i]}
    rge = max[:objectives][i] - min[:objectives][i]
    pop.first[:dist], pop.last[:dist] = 1.0/0.0, 1.0/0.0
    next if rge == 0.0
    (1...(pop.size-1)).each do |j|
      pop[j][:dist]+=(pop[j+1][:objectives][i]-pop[j-1][:objectives][i])/rge
    end
  end
end