[Bug-gsl] [bug #40755] Sporadic nan's from gsl_sf_bessel_Jn an related functions

[Rhys Ulerich]

URL:
  <http://savannah.gnu.org/bugs/?40755>

                 Summary: Sporadic nan's from gsl_sf_bessel_Jn an related
functions
                 Project: GNU Scientific Library
            Submitted by: rhysu
            Submitted on: Sat 30 Nov 2013 04:27:29 PM GMT
                Category: Accuracy problem
                Severity: 3 - Normal
        Operating System: 
                  Status: None
             Assigned to: None
             Open/Closed: Open
                 Release: 
         Discussion Lock: Any

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Details:

>From http://lists.gnu.org/archive/html/bug-gsl/2013-11/msg00008.html and
behavior confirmed on GSL 1.16:

I think this is distinct from other bugs in the gsl bug database. No error is
reported by gsl_sf_bessel_Jn_e.

$ cat testgsl.c
/*
** Bug in gsl_sf_bessel_Jn (and related functions)
*/

#include <stdio.h>
#include <math.h>
#include <gsl/gsl_sf_bessel.h>

int main (int argc, char **argv) {
  double x = M_PI * 128 * 127.999;
  int nmin = 46335, nmax = 46345, i;
  for (i = nmin; i <= nmax; ++i) {
    double gsl_res = gsl_sf_bessel_Jn (i, x);
    double sys_res = jn (i, x);
    printf ("For (%d, %f), gsl gave %f, jn() gave %f\n", i, x, gsl_res,
        sys_res);
  }
  return 0;
}
$ gcc -O testgsl.c -o testgsl -lgsl -lgslcblas -lm
$ ./testgsl
For (46335, 51471.451913), gsl gave -0.004580, jn() gave -0.004580
For (46336, 51471.451913), gsl gave -0.005310, jn() gave -0.005310
For (46337, 51471.451913), gsl gave -0.004980, jn() gave -0.004980
For (46338, 51471.451913), gsl gave -0.003657, jn() gave -0.003657
For (46339, 51471.451913), gsl gave -0.001604, jn() gave -0.001604
For (46340, 51471.451913), gsl gave 0.000769, jn() gave 0.000769
For (46341, 51471.451913), gsl gave -nan, jn() gave 0.002988
For (46342, 51471.451913), gsl gave -nan, jn() gave 0.004612
For (46343, 51471.451913), gsl gave -nan, jn() gave 0.005316
For (46344, 51471.451913), gsl gave -nan, jn() gave 0.004961
For (46345, 51471.451913), gsl gave -nan, jn() gave 0.003618


Thanks
Paul




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