Re: [Help-gsl] Adaptive numerical integration of in-built distribution function

[Martin Jansche]

Are you trying to figure out how to use adaptive integration in general, or
do you primarily need integrals of the beta PDF? If the latter, would a
combination of gsl_cdf_beta_P and gsl_cdf_beta_Q do what you want?
-- mj

On Wed, Dec 27, 2017 at 8:53 PM, Vasu Jaganath <address@hidden>
wrote:

> Hi group!
>
> I would like to know how to do  adaptive integration of beta PDF
> distribution function. (The PDF not the random number generator)
>
> I'm trying to follow this example (given in the official docs),
>
> #include <stdio.h>#include <math.h>#include
> <gsl/gsl_integration.h>#include <gsl/gsl_randist.h>
> double f (double x, void * params) {
>     double alpha = *(double *) params;
>     double f = log(alpha*x) / sqrt(x);
>     return f;}
> int main (void){
>     gsl_integration_workspace * w
>     = gsl_integration_workspace_alloc (1000);
>
>     double result, error;
>     double expected = -4.0;
>     double alpha = 1.0;
>
>     gsl_function F;
>     F.function = &f;
>     //F.function = &gsl_ran_gaussian_pdf;
>     //F.function = gsl_ran_beta_pdf
>     F.params = &alpha;
>
>     gsl_integration_qags (&F, 0, 1, 0, 1e-7, 1000,
>                     w, &result, &error);
>
>     printf ("result          = % .18f\n", result);
>     printf ("exact result    = % .18f\n", expected);
>     printf ("estimated error = % .18f\n", error);
>     printf ("actual error    = % .18f\n", result - expected);
>     printf ("intervals       = %zu\n", w->size);
>
>     gsl_integration_workspace_free (w);
>
>     return 0;
>
> }
>
> I don't know how to use the inbuilt function and how to specify more than 1
> parameters (alpha and beta) to the function. I am very new to gsl, so
> please bear with me.
>
> I tried to integrate gsl_ran_gaussian_pdf from 0 to 1 with sigma = 0.001,
> but I wasn't able to do it.
>
> Any help or further direction to appropriate docs would be appreciated!
>
> Thanks,
> Vasu
>