| /* |
| * Mathlib : A C Library of Special Functions |
| * Copyright (C) 1998 Ross Ihaka |
| * Copyright (C) 2000 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 distribution function of the Poisson distribution. |
| */ |
| |
| #include "nmath.h" |
| #include "dpq.h" |
| |
| double ppois(double x, double lambda, int lower_tail, int log_p) |
| { |
| #ifdef IEEE_754 |
| if (ISNAN(x) || ISNAN(lambda)) |
| return x + lambda; |
| #endif |
| if(lambda < 0.) ML_ERR_return_NAN; |
| if (x < 0) return R_DT_0; |
| if (lambda == 0.) return R_DT_1; |
| if (!R_FINITE(x)) return R_DT_1; |
| x = floor(x + 1e-7); |
| |
| return pgamma(lambda, x + 1, 1., !lower_tail, log_p); |
| } |