Resistor combinations (serial, parallel) using GP ( https://github.com/phorsfall/genetics/ )

resist.rb

$:.unshift("lib")
require "genetics"
require "pp"

class Resist < Tree
  TARGET = 215

  literals [50, 100, 500]

  function(:para) { |a,b| (a*b)/(a+b) }
  function(:ser) { |a,b| a + b }

  def fitness
    @fitness ||= begin
      value = (TARGET - evaluate).abs + 5*leaf_count + ballance
      value
    end
  end

  def leaf_count(node = genes)
    node[0] == :call ? (node[2..-1].map { |n| leaf_count(n) }.inject(:+)) : 1
  end

  def ballance(node = genes)
    return 0 if node[0] != :call
    depths = node[2..-1].map { |n| depth(n) } || [0]
    depths.max - depths.min
  end
end


population = Population.new(Resist, :select_with => Tournament, :size => 50)

population.evolve(1000) do |g|
  print "."
  $stdout.flush
end

winner = population.fittest
puts
pp winner.genes
puts
puts "Value: #{winner.evaluate} Ohms, resistors: #{winner.leaf_count}"