Golden Section Routine Segmentation Fault - c

Question

I'm trying to find minimum point of Gamma function by Golden Section method. But when I execute the program I get segmentation fault error. I think since I'm a newbie C user, the problem may be due to calling the function Min_Search_Golden_Section wrong. Here is my complete code. I can't find my mistake. Thanks in advance.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <float.h>
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
#define A 12
#define sqrt5 2.236067977499789696
static int Stopping_Rule(double x0, double x1, double tolerance);
double sp_gamma(double z)
{
const int a = A;
static double c_space[A];
static double *c = NULL;
int k;
double accm;
if ( c == NULL ) {
double k1_factrl = 1.0; /* (k - 1)!*(-1)^k with 0!==1*/
c = c_space;
c[0] = sqrt(2.0*M_PI);
for(k=1; k < a; k++) {
c[k] = exp(a-k) * pow(a-k, k-0.5) / k1_factrl;
k1_factrl *= -k;
}
}
accm = c[0];
for(k=1; k < a; k++) {
accm += c[k] / ( z + k );
}
accm *= exp(-(z+a)) * pow(z+a, z+0.5); /* Gamma(z+1) */
return accm/z;
}
void Min_Search_Golden_Section( double (*f)(double), double* a, double *fa,
double* b, double* fb, double tolerance)
{
static const double lambda = 0.5 * (sqrt5 - 1.0);
static const double mu = 0.5 * (3.0 - sqrt5); // = 1 - lambda
double x1;
double x2;
double fx1;
double fx2;
// Find first two internal points and evaluate
// the function at the two internal points.
x1 = *b - lambda * (*b - *a);
x2 = *a + lambda * (*b - *a);
fx1 = f(x1);
fx2 = f(x2);
// Verify that the tolerance is an acceptable number
if (tolerance <= 0.0) tolerance = sqrt(DBL_EPSILON) * (*b - *a);
// Loop by exluding segments from current endpoints a, b
// to current internal points x1, x2 and then calculating
// a new internal point until the length of the interval
// is less than or equal to the tolerance.
while ( ! Stopping_Rule( *a, *b, tolerance) ) {
if (fx1 > fx2) {
*a = x1;
*fa = fx1;
if ( Stopping_Rule( *a, *b, tolerance) ) break;
x1 = x2;
fx1 = fx2;
x2 = *b - mu * (*b - *a);
fx2 = f(x2);
} else {
*b = x2;
*fb = fx2;
if ( Stopping_Rule( *a, *b, tolerance) ) break;
x2 = x1;
fx2 = fx1;
x1 = *a + mu * (*b - *a);
fx1 = f(x1);
}
}
return;
}
int main()
{
double x;
double a = 0.0, b = 4.0, fa = 0.00001, fb = 6.0;
double fx = sp_gamma(x);
Min_Search_Golden_Section( &fx, &a, &fa, &b, &fb, 0.0000001);
return 0;
}
static int Stopping_Rule(double x0, double x1, double tolerance)
{
double xm = 0.5 * fabs( x1 + x0 );
if ( xm <= 1.0 ) return ( fabs( x1 - x0 ) < tolerance ) ? 1 : 0;
return ( fabs( x1 - x0 ) < tolerance * xm ) ? 1 : 0;
}

Answer 1

You should be getting a compiler error. The first argument to Min_Search_Golden_Section should be a function pointer, but you pass the address of a variable instead.
When you get compiler errors, fix them - don't run the program and hope. :)
I guess you just meant to write:
Min_Search_Golden_Section( &sp_gamma, &a, &fa, &b, &fb, 0.0000001);