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

#define FROM   0.0
#define TO   100.0
#define TAU   0.001

typedef struct NEURON {
    double output, old_output;
    int    Ninp;
    double *inp_wgt;
    struct NEURON **inp_neuron;
} neuron;

void initialize_neuron(neuron *a, int N)
{
    int i;

    a->output = 0.0;
    a->Ninp = N;
    a->inp_wgt = (double *)malloc(sizeof(double) * (N));
    if ( a->inp_wgt == NULL ) {
        fprintf(stderr,"### malloc() faild.\n");
        exit (EXIT_FAILURE);
    }
    for (i=0; i< a->Ninp; i++) {
        a->inp_wgt[i] = 0.0;
    }
    a->inp_neuron = (neuron **)malloc(sizeof(neuron *) * (N));
    if ( a->inp_neuron == NULL ) {
        fprintf(stderr,"### malloc() faild.\n");
        exit (EXIT_FAILURE);
    }
}

double output_f(double value)
{
    return value;
}

void calc_neuron(neuron *a)
{
    double wrk;
    int i;

    wrk = 0.0;
    for(i=0; i< a->Ninp; i++){
        wrk += a->inp_wgt[i] * a->inp_neuron[i]->old_output;
    }
    a->output += output_f(wrk) * TAU;
}

void update_neuron(neuron *a)
{
    a->old_output = a->output;
}

int main_loop( neuron *a, neuron *b)
{
    double t = FROM;
    while ( t <= TO ){
        printf("%6.3f %7.4f %7.4f\n", t, a->output, b->output);
        calc_neuron(a);     calc_neuron(b); 
        update_neuron(a);     update_neuron(b); 
        t += TAU;
    }
    return 0;
}

int main(int argc, char **argv)
{
    neuron x, y;

    if ( argc != 3 ) {
        printf("### Usage: %s <double> <double>\n", argv[0]);
        exit (EXIT_FAILURE);
    }

    initialize_neuron(&x, 2);
    initialize_neuron(&y, 2);

    x.output = x.old_output = atof(argv[1]);
    y.output = y.old_output = atof(argv[2]);

    x.inp_neuron[0] = &x;
    x.inp_neuron[1] = &y;
    y.inp_neuron[0] = &y;
    y.inp_neuron[1] = &x;

    x.inp_wgt[0] = 0.0; /* w_{xx} */
    x.inp_wgt[1] = 1.0; /* w_{xy} */
    y.inp_wgt[1] = -1.0; /* w_{yx} */
    y.inp_wgt[0] = 0.0; /* w_{yy} */

    return main_loop(&x, &y);
}