# File lib/ai4r/genetic_algorithm/genetic_algorithm.rb, line 176
      def fitness
        return @fitness if @fitness
        last_token = @data[0]
        cost = 0
        @data[1..-1].each do |token|
          cost += @@costs[last_token][token]
          last_token = token
        end
        @fitness = -1 * cost
        return @fitness
      end