/* ------------------------------------------------------------- */
/* File: example2.c */
/* ------------------------------------------------------------- */
/* Include UNURAN header file. */
#include <unuran.h>
/* ------------------------------------------------------------- */
/* In this example we build a distribution object from scratch */
/* and sample from this distribution. */
/* */
/* We use method TDR (Transformed Density Rejection) which */
/* required a PDF and the derivative of the PDF. */
/* ------------------------------------------------------------- */
/* Define the PDF and dPDF of our distribution. */
/* */
/* Our distribution has the PDF */
/* */
/* / 1 - x*x if |x| <= 1 */
/* f(x) = < */
/* \ 0 otherwise */
/* */
/* The PDF of our distribution: */
double mypdf( double x, const UNUR_DISTR *distr )
/* The second argument (`distr') can be used for parameters */
/* for the PDF. (We do not use parameters in our example.) */
{
if (fabs(x) >= 1.)
return 0.;
else
return (1.-x*x);
} /* end of mypdf() */
/* The derivative of the PDF of our distribution: */
double mydpdf( double x, const UNUR_DISTR *distr )
{
if (fabs(x) >= 1.)
return 0.;
else
return (-2.*x);
} /* end of mydpdf() */
/* ------------------------------------------------------------- */
int main(void)
{
int i; /* loop variable */
double x; /* will hold the random number */
/* Declare the three UNURAN objects. */
UNUR_DISTR *distr; /* distribution object */
UNUR_PAR *par; /* parameter object */
UNUR_GEN *gen; /* generator object */
/* Create a new distribution object from scratch. */
/* It is a continuous distribution, and we need a PDF and the */
/* derivative of the PDF. Moreover we set the domain. */
/* Get empty distribution object for a continuous distribution */
distr = unur_distr_cont_new();
/* Assign the PDF and dPDF (defined above). */
unur_distr_cont_set_pdf( distr, mypdf );
unur_distr_cont_set_dpdf( distr, mydpdf );
/* Set the domain of the distribution (optional for TDR). */
unur_distr_cont_set_domain( distr, -1., 1. );
/* Choose a method: TDR. */
par = unur_tdr_new(distr);
/* Now you can change some of the default settings for the */
/* parameters of the chosen method. We don't do it here. */
/* Create the generator object. */
gen = unur_init(par);
/* Notice that this call has also destroyed the parameter */
/* object `par' as a side effect. */
/* It is important to check if the creation of the generator */
/* object was successful. Otherwise `gen' is the NULL pointer */
/* and would cause a segmentation fault if used for sampling. */
if (gen == NULL) {
fprintf(stderr, "ERROR: cannot create generator object\n");
exit (EXIT_FAILURE);
}
/* It is possible to reuse the distribution object to create */
/* another generator object. If you do not need it any more, */
/* it should be destroyed to free memory. */
unur_distr_free(distr);
/* Now you can use the generator object `gen' to sample from */
/* the distribution. Eg.: */
for (i=0; i<10; i++) {
x = unur_sample_cont(gen);
printf("%f\n",x);
}
/* When you do not need the generator object any more, you */
/* can destroy it. */
unur_free(gen);
exit (EXIT_SUCCESS);
} /* end of main() */
/* ------------------------------------------------------------- */
