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/* randist/pascal.c
*
* Copyright (C) 1996, 1997, 1998, 1999, 2000 James Theiler, Brian Gough
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or (at
* your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
#include <config.h>
#include <math.h>
#include <gsl/gsl_rng.h>
#include <gsl/gsl_randist.h>
/* The Pascal distribution is a negative binomial with valued integer n
prob(k) = (n - 1 + k)!/(n!(k - 1)!) * p^n (1-p)^k for k = 0, 1, ..., n
*/
unsigned int
gsl_ran_pascal (const gsl_rng * r, double p, unsigned int n)
{
/* This is a separate interface for the pascal distribution so that
it can be optimized differently from the negative binomial in
future.
e.g. if n < 10 it might be faster to generate the Pascal
distributions as the sum of geometric variates directly. */
unsigned int k = gsl_ran_negative_binomial (r, p, (double) n);
return k;
}
double
gsl_ran_pascal_pdf (const unsigned int k, const double p, unsigned int n)
{
double P = gsl_ran_negative_binomial_pdf (k, p, (double) n);
return P;
}
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