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/* randist/pascal.c
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*
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* Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 James Theiler, Brian Gough
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3 of the License, or (at
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* your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
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*/
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#include <config.h>
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#include <math.h>
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#include <gsl/gsl_rng.h>
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#include <gsl/gsl_randist.h>
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/* The Pascal distribution is a negative binomial with valued integer n
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prob(k) = (n - 1 + k)!/(n!(k - 1)!) * p^n (1-p)^k for k = 0, 1, ..., n
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*/
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unsigned int
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gsl_ran_pascal (const gsl_rng * r, double p, unsigned int n)
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{
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/* This is a separate interface for the pascal distribution so that
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it can be optimized differently from the negative binomial in
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future.
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e.g. if n < 10 it might be faster to generate the Pascal
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distributions as the sum of geometric variates directly. */
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unsigned int k = gsl_ran_negative_binomial (r, p, (double) n);
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return k;
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}
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double
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gsl_ran_pascal_pdf (const unsigned int k, const double p, unsigned int n)
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{
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double P = gsl_ran_negative_binomial_pdf (k, p, (double) n);
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return P;
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}
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