Re: [Bug-gsl] gsl_sf_beta_inc returns 0.0 all the time

[Alejandro Cámara Iglesias]

Not an expert, but I have an idea.

Try to create and initialize the from_gsl variable outside the for loop.
Maybe the compiler optimizes the code somehow and executes the printf();
command before initializing the from_gsl variable with the function return
value.

Code:
int main(int argc, char **argv) {
   long i;
   double x = 0.0;
   double a = 0.5;
   double b = 0.5;
   double from_gsl = 0.0;
   for (i=0; i < 10; i++) {
       x += 1.0/10.1;
       from_gsl = gsl_sf_beta_inc(a,b,x);
       printf("a:%f b:%f x:%f betai(a,b,x):%f \n",a,b,x,from_gsl);
   }
   return 0;
}

This may sound nuts, but I'll try it if you haven't yet.

Good luck!

*Alejandro Cámara*
PhD Student of GICO <http://www.ucm.es/info/giboucm/>



2010/12/22 Andrew Schein <address@hidden>

> I first produced this error on Ubuntu gsl0-dev package 1.13+dfsg-1 on
> Ubuntu
> 10.04 (x86_64), but then downloaded gsl-1.13.tar.gz and compiled from
> source
> (same machine).
>
> Attached is a short program that attempts to reproduce a portion of the
> incomplete beta curve for comparison against a plot shown in Numerical
> Recipes in C++.  The numerical recipes plot varies x between (0,1) while
> setting a=b=0.5.
>
> #include <stdio.h>
> #include <gsl/gsl_rng.h>
>
> int main(int argc, char **argv) {
>    long i;
>    double x = 0.0;
>    double a = 0.5;
>    double b = 0.5;
>    for (i=0; i < 10; i++) {
>        x += 1.0/10.1;
>        double from_gsl = gsl_sf_beta_inc(a,b,x);
>        printf("a:%f b:%f x:%f betai(a,b,x):%f \n",a,b,x,from_gsl);
>    }
>    return 0;
> }
>
> The output is:
>
> $ ./test_betai
> a:0.500000 b:0.500000 x:0.099010 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.198020 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.297030 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.396040 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.495050 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.594059 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.693069 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.792079 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.891089 betai(a,b,x):0.000000
> a:0.500000 b:0.500000 x:0.990099 betai(a,b,x):0.000000
> $
>
> Thanks,
>
> Andy
>
> --
> Andrew I. Schein
> www.andrewschein.com
> _______________________________________________
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>