/* S4MIN.C
xref:
input:
output:
does: Scan for a minimum of a function in an interval
*/
/************************************************************/

#include "mtb.h"

/************************************************************/

void s4min  (double f(double), double lower, double upper, int n,
            double *x_min,  double *f_min)

        /* scan the interval [lower, upper] for a min of f() */
        /* evaluate f() at n points in the interval */
{
  double d, x, fx;

  if (lower>upper) {d=upper; upper=lower; lower=d;} /* swap */
  else if (lower==upper) {
    *x_min=upper;
    *f_min=f(upper);
    return;
  }
  if (n < 2)  n = 2;

  d = (upper - lower) / (n-1);
  *x_min = lower;
  *f_min = f(*x_min);

  for (x = lower+d; x <= upper; x += d) {
    fx = f(x);
    if (fx < *f_min)  {*x_min = x; *f_min = fx;}
  }
}