# File lib/ai4r/neural_network/backpropagation.rb, line 173
      def feedforward(input_values)
        input_values.each_index do |input_index| 
          @activation_nodes.first[input_index] = input_values[input_index]
        end
        @weights.each_index do |n|
          @structure[n+1].times do |j|
            sum = 0.0
            @activation_nodes[n].each_index do |i|
              sum += (@activation_nodes[n][i] * @weights[n][i][j])
            end
            @activation_nodes[n+1][j] = @propagation_function.call(sum)
          end
        end        
      end