| /* |
| * Mathlib : A C Library of Special Functions |
| * Copyright (C) 1998 Ross Ihaka |
| * Copyright (C) 2000-6 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 |
| * |
| * The density function of the Weibull distribution. |
| */ |
| |
| #include "nmath.h" |
| #include "dpq.h" |
| |
| double dweibull(double x, double shape, double scale, int give_log) |
| { |
| double tmp1, tmp2; |
| #ifdef IEEE_754 |
| if (ISNAN(x) || ISNAN(shape) || ISNAN(scale)) |
| return x + shape + scale; |
| #endif |
| if (shape <= 0 || scale <= 0) ML_ERR_return_NAN; |
| |
| if (x < 0) return R_D__0; |
| if (!R_FINITE(x)) return R_D__0; |
| /* need to handle x == 0 separately */ |
| if(x == 0 && shape < 1) return ML_POSINF; |
| tmp1 = pow(x / scale, shape - 1); |
| tmp2 = tmp1 * (x / scale); |
| /* These are incorrect if tmp1 == 0 */ |
| return give_log ? |
| -tmp2 + log(shape * tmp1 / scale) : |
| shape * tmp1 * exp(-tmp2) / scale; |
| } |