3 * Copyright (C) 1996, 1997, 1998, 1999, 2000, 2007 James Theiler, Brian Gough
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 3 of the License, or (at
8 * your option) any later version.
10 * This program is distributed in the hope that it will be useful, but
11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
22 #include <gsl/gsl_math.h>
23 #include <gsl/gsl_rng.h>
24 #include <gsl/gsl_randist.h>
25 #include <gsl/gsl_sf_erf.h>
28 gsl_ran_gaussian_tail (const gsl_rng * r, const double a, const double sigma)
30 /* Returns a gaussian random variable larger than a
31 * This implementation does one-sided upper-tailed deviates.
38 /* For small s, use a direct rejection method. The limit s < 1
39 can be adjusted to optimise the overall efficiency */
45 x = gsl_ran_gaussian (r, 1.0);
52 /* Use the "supertail" deviates from the last two steps
53 * of Marsaglia's rectangle-wedge-tail method, as described
54 * in Knuth, v2, 3rd ed, pp 123-128. (See also exercise 11, p139,
55 * and the solution, p586.)
62 u = gsl_rng_uniform (r);
65 v = gsl_rng_uniform (r);
68 x = sqrt (s * s - 2 * log (v));
76 gsl_ran_gaussian_tail_pdf (const double x, const double a, const double sigma)
85 double u = x / sigma ;
87 double f = gsl_sf_erfc (a / (sqrt (2.0) * sigma));
91 p = (1 / (N * sqrt (2 * M_PI) * sigma)) * exp (-u * u / 2);
98 gsl_ran_ugaussian_tail (const gsl_rng * r, const double a)
100 return gsl_ran_gaussian_tail (r, a, 1.0) ;
104 gsl_ran_ugaussian_tail_pdf (const double x, const double a)
106 return gsl_ran_gaussian_tail_pdf (x, a, 1.0) ;