backw

#pragma hdrstop
#pragma argsused

#ifdef _WIN32
#include <tchar.h>
#else
  typedef char _TCHAR;
  #define _tmain main
#endif

#include <stdio.h>
#include <math.h>


int i;
const double learning_rate = 0.1;
double node_b_cost_function, node_b_cost_function_derivative, node_b_cost_function_gradient, node_a_cost_function_gradient;
double node_a_input, node_b_input;
double node_a_weight, node_b_weight;
double node_a_output, node_b_output;
double node_b_desired_output;

//NETWORK SIMPLE         "node a"  O-----------O  "node b"


double node_x_function(double x)
{
    return 1 / (1 + exp(-(x)));
}

double node_x_function_derivative(double x)
{
     return x * (1 - x);
}

int _tmain(int argc, _TCHAR* argv[])
{

    node_a_input = 0.02;
    node_a_weight = 0.32; node_b_weight = 0.15;
    node_b_desired_output = 0.005;

  for (i; i < 3000000; i++) {


                        node_a_output = node_x_function(node_a_input*node_a_weight);

                        node_b_input = node_a_output;
                        node_b_output = node_x_function(node_b_input*node_b_weight);

                        //needs forward propagation in here, comes later

                        //


                        //backward propagation simple test
                        node_b_cost_function = pow(node_x_function(node_b_desired_output) - node_b_output,2);
                        //node_b_cost_function_derivative = 2*(node_x_function(node_b_desired_output) - node_b_output);
                        node_b_cost_function_derivative = 2*(node_b_desired_output - node_b_output);

                        node_b_cost_function_gradient =  node_x_function_derivative(node_b_output) * node_b_cost_function_derivative;
                        node_a_cost_function_gradient =  node_x_function_derivative(node_a_output)  * node_b_weight * node_b_cost_function_gradient;

                        node_b_weight = node_b_weight + learning_rate * node_b_cost_function_gradient;
                        node_a_weight = node_a_weight + learning_rate * node_a_cost_function_gradient;



                        printf("\nout: %.15lf %.15lf %.15lf %.15lf %.15lf", node_a_input, node_b_input, node_a_output, node_b_output, node_b_desired_output);
                        printf("\nout: %.15lf %.15lf", node_b_cost_function, node_b_cost_function_derivative);
                      }

    scanf("%d",&i);
    return 0;
}