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

#define FROM -10.0
#define TO    10.0
#define STEP  0.01

typedef struct NEURON {
    double output, old_output;
    int N;
    double *weights;
    struct NEURON **input_neuron;
    double (*outputf)();
} neuron;

double sigmoid( double x )
{
    return 1.0 / ( 1.0 + exp ( -x ) );
}

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

    a->output = 0.0;
    a->old_output = 0.0;
    a->N = N;
    a->weights = (double *)malloc(sizeof(double) * N);
    if ( a->weights == NULL ) {
        fprintf(stderr, "### malloc() failed.\n");
        exit (EXIT_FAILURE);
    }
    for ( i=0; i<a->N; i++ ) {
        a->weights[i] = 0.0;
    }
    a->input_neuron = (neuron **)malloc(sizeof (neuron *) * N);
    if ( a->input_neuron == NULL ) {
        fprintf(stderr, "### malloc() failed.\n");
        exit (EXIT_FAILURE);
    }
    a->outputf = sigmoid;
    return EXIT_SUCCESS;
}

void calc_output ( neuron *a )
{
    int i;
    double wrk = 0.0;

    for ( i=0; i<a->N; i++ ) {
        wrk += a->weights[i] * a->input_neuron[i]->output;
    }
    a->output = a->outputf( wrk );
}
    
int main(void)
{
    neuron output, input;

    initialize_neuron( &output, 1 );
    initialize_neuron( &input, 0 );
    
    output.input_neuron[0] = &input;
    output.weights[0] = 1.0;

    for (input.output=FROM; input.output<=TO;input.output += STEP){
        calc_output( &output );
        fprintf(stdout, "%5.3f %7.3f\n", 
                         input.output, output.output);
    }

    return 0;
}