| /* |
| * Mathlib : A C Library of Special Functions |
| * Copyright (C) 1998 Ross Ihaka |
| * Copyright (C) 2000-2008 The R Core Team |
| * |
| * 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, a copy is available at |
| * https://www.R-project.org/Licenses/ |
| * |
| * DESCRIPTION |
| * |
| * Pseudo-random variates from a t distribution. |
| * |
| * NOTES |
| * |
| * This function calls rchisq and rnorm to do the real work. |
| */ |
| |
| #include "nmath.h" |
| |
| double rt(double df) |
| { |
| if (ISNAN(df) || df <= 0.0) ML_WARN_return_NAN; |
| |
| if(!R_FINITE(df)) |
| return norm_rand(); |
| else { |
| /* Some compilers (including MW6) evaluated this from right to left |
| return norm_rand() / sqrt(rchisq(df) / df); */ |
| double num = norm_rand(); |
| return num / sqrt(rchisq(df) / df); |
| } |
| } |