#ifndef _NEURON_UTIL_H_
#define _NEURON_UTIL_H

#include "general.h"

/* Definition of a neuron                            */
/* Among the members of the following structure,     */
/*  Ninp strands for a number of input from neurons. */
struct NEURON {
    double output;              /* Output values of this neuron */
    int Ninp;                   /* Number of input neurons */
    double *inp_wgt;            /* array of input weights */
    struct NEURON **inp_neuron; /* the pointer to the input neurons */
    double (*output_func)();    /* the pointer to the output function */
    double (*Doutput_func)();   /* the pointer to the differenctial above */
};
typedef struct NEURON neuron;

/* McCallogh and Pitts' formal neuron */ 
double formal_f(double state);

/* Logistic function $f(x)=1/(1+ exp(-x))$ */
double logistic_f(double state);
double Dlogistic_f(double state);

/* Hyperbolic function $f(x)= 1/2 * ( tanh(x) + 1) */
double hyperbolic_f(double state);
double Dhyperbolic_f(double state);

/* liner output function */
double liner_f(double state);
double Dliner_f(double state);

/* initialize a neuron which has N inputs */
void initialize_neuron(neuron *a, int N, double (*output_func)(), double (*Doutput_func)());

/* copy whole contents from a to b */
void copy_neuron(neuron *a, neuron *b);

void calc_neuron (neuron *a);
void update_wgt(neuron *a, double error);

#endif /* !_NEURON_UTIL_H */