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- /* randist/gumbel.c
- *
- * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 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 3 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 "gsl__config.h"
- #include <math.h>
- #include "gsl_rng.h"
- #include "gsl_randist.h"
- /* The Type I Gumbel distribution has the form,
- p(x) dx = a b exp(-(b exp(-ax) + ax)) dx
- and the Type II Gumbel distribution has the form,
- p(x) dx = b a x^-(a+1) exp(-b x^-a)) dx
- */
- double
- gsl_ran_gumbel1 (const gsl_rng * r, const double a, const double b)
- {
- double x = gsl_rng_uniform_pos (r);
- double z = (log(b) - log(-log(x))) / a;
- return z;
- }
- double
- gsl_ran_gumbel1_pdf (const double x, const double a, const double b)
- {
- double p = a * b * exp (-(b * exp(-a * x) + a * x));
- return p;
- }
- double
- gsl_ran_gumbel2 (const gsl_rng * r, const double a, const double b)
- {
- double x = gsl_rng_uniform_pos (r);
- double z = pow(-b / log(x), 1/a);
- return z;
- }
- double
- gsl_ran_gumbel2_pdf (const double x, const double a, const double b)
- {
- if (x <= 0)
- {
- return 0 ;
- }
- else
- {
- double p = b * a * pow(x,-(a+1)) * exp (-b * pow(x, -a));
- return p;
- }
- }
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