| /* |
| * AUTHOR |
| * Catherine Loader, catherine@research.bell-labs.com. |
| * October 23, 2000. |
| * |
| * Merge in to R: |
| * Copyright (C) 2000-2016 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 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, a copy is available at |
| * https://www.R-project.org/Licenses/ |
| * |
| * |
| * DESCRIPTION |
| * |
| * dpois() checks argument validity and calls dpois_raw(). |
| * |
| * dpois_raw() computes the Poisson probability lb^x exp(-lb) / x!. |
| * This does not check that x is an integer, since dgamma() may |
| * call this with a fractional x argument. Any necessary argument |
| * checks should be done in the calling function. |
| * |
| */ |
| |
| #include "nmath.h" |
| #include "dpq.h" |
| |
| // called also from dgamma.c, pgamma.c, dnbeta.c, dnbinom.c, dnchisq.c : |
| double dpois_raw(double x, double lambda, int give_log) |
| { |
| /* x >= 0 ; integer for dpois(), but not e.g. for pgamma()! |
| lambda >= 0 |
| */ |
| if (lambda == 0) return( (x == 0) ? R_D__1 : R_D__0 ); |
| if (!R_FINITE(lambda)) return R_D__0; // including for the case where x = lambda = +Inf |
| if (x < 0) return( R_D__0 ); |
| if (x <= lambda * DBL_MIN) return(R_D_exp(-lambda) ); |
| if (lambda < x * DBL_MIN) { |
| if (!R_FINITE(x)) // lambda < x = +Inf |
| return R_D__0; |
| // else |
| return(R_D_exp(-lambda + x*log(lambda) -lgammafn(x+1))); |
| } |
| return(R_D_fexp( M_2PI*x, -stirlerr(x)-bd0(x,lambda) )); |
| } |
| |
| double dpois(double x, double lambda, int give_log) |
| { |
| #ifdef IEEE_754 |
| if(ISNAN(x) || ISNAN(lambda)) |
| return x + lambda; |
| #endif |
| |
| if (lambda < 0) ML_ERR_return_NAN; |
| R_D_nonint_check(x); |
| if (x < 0 || !R_FINITE(x)) |
| return R_D__0; |
| |
| x = R_forceint(x); |
| |
| return( dpois_raw(x,lambda,give_log) ); |
| } |