Re: [Help-gsl] RNG and threads

[Torquil Macdonald Sørensen]

Warren Weckesser wrote:
> This has nothing to do with threads.  Check this out:
>
> ----------
> #include <stdio.h>
> #include <gsl/gsl_rng.h>
>
> int main (void)
>     {
>     const gsl_rng_type * T;
>     gsl_rng *r1, *r2, *r3;
>     int i, n = 10;
>
>     gsl_rng_env_setup();
>
>     T = gsl_rng_ranlxs0;
>    
>     r1 = gsl_rng_alloc(T);
>     r2 = gsl_rng_alloc(T);
>     r3 = gsl_rng_alloc(T);
>     gsl_rng_set(r1,0);
>     gsl_rng_set(r2,1);
>     gsl_rng_set(r3,2);
>
>     for (i = 0; i < n; i++)
>         {
>         double u1 = gsl_rng_uniform (r1);
>         double u2 = gsl_rng_uniform (r2);
>         double u3 = gsl_rng_uniform (r3);
>         printf ("%.11f %.11f %.11f\n", u1,u2, u3);
>         }
>
>     gsl_rng_free (r1);
>     gsl_rng_free (r2);
>     gsl_rng_free (r3);
>     return 0;
>     }
> ----------
> Compile and run:
> ----------
> $ gcc gslrngtest.c -lgsl -o gslrngtest
> $ ./gslrngtest
> 0.32085895538 0.32085895538 0.16047435999
> 0.49408543110 0.49408543110 0.24704271555
> 0.70446860790 0.70446860790 0.35229921341
> 0.81177759171 0.81177759171 0.40588879585
> 0.65004783869 0.65004783869 0.32499593496
> 0.75581908226 0.75581908226 0.87790954113
> 0.16959655285 0.16959655285 0.08471691608
> 0.24530410767 0.24530410767 0.12265205383
> 0.18674021959 0.18674021959 0.59334981441
> 0.62624281645 0.62624281645 0.31312137842
> $
> ----------
> My guess as to why the first two columns are the same is based on this 
> quote from the docs:
>
> "If the seed s is zero then the standard seed from the original 
> implementation is used instead."
>
> Perhaps the "standard seed from the original implementation" of ranlxs0 
> algorithm is 1.
>
> Warren

Thanks Warren, I now remember that I had read somewhere in the 
documentation that seed=0 gives the default seed, so I should have 
suspected something. When I seed with 1,2,3... I get different results 
in each thread for all the different RNGs that I am trying.

Thanks,
Torquil Soerensen