gnc_numeric Example

EXAMPLE

The following program finds the best gnc_numeric approximation to the math.h constant M_PI given a maximum denominator. For large denominators, the gnc_numeric approximation is accurate to more decimal places than will generally be needed, but in some cases this may not be good enough. For example,

    M_PI                   = 3.14159265358979323846
    245850922 / 78256779   = 3.14159265358979311599  (16 sig figs)
    3126535 / 995207       = 3.14159265358865047446  (12 sig figs)
    355 / 113              = 3.14159292035398252096  (7 sig figs)

#include <glib.h>
#include <qof.h>
#include <math.h>

int
main(int argc, char ** argv)
{
  gnc_numeric approx, best;
  double err, best_err=1.0;
  double m_pi = M_PI;
  gint64 denom;
  gint64 max;

  sscanf(argv[1], "%Ld", &max);
  
  for (denom = 1; denom < max; denom++)
  {
    approx = double_to_gnc_numeric (m_pi, denom, GNC_RND_ROUND);
    err    = m_pi - gnc_numeric_to_double (approx);
    if (fabs (err) < fabs (best_err))
    {
      best = approx;
      best_err = err;
      printf ("%Ld / %Ld = %.30f\n", gnc_numeric_num (best),
              gnc_numeric_denom (best), gnc_numeric_to_double (best));
    }
  }
}