| /* |
| * AUTHOR |
| * Catherine Loader, catherine@research.bell-labs.com. |
| * October 23, 2000. |
| * |
| * Merge in to R: |
| * Copyright (C) 2000-2014 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 |
| * Evaluates the "deviance part" |
| * bd0(x,M) := M * D0(x/M) = M*[ x/M * log(x/M) + 1 - (x/M) ] = |
| * = x * log(x/M) + M - x |
| * where M = E[X] = n*p (or = lambda), for x, M > 0 |
| * |
| * in a manner that should be stable (with small relative error) |
| * for all x and M=np. In particular for x/np close to 1, direct |
| * evaluation fails, and evaluation is based on the Taylor series |
| * of log((1+v)/(1-v)) with v = (x-M)/(x+M) = (x-np)/(x+np). |
| */ |
| #include "nmath.h" |
| |
| double attribute_hidden bd0(double x, double np) |
| { |
| double ej, s, s1, v; |
| int j; |
| |
| if(!R_FINITE(x) || !R_FINITE(np) || np == 0.0) ML_ERR_return_NAN; |
| |
| if (fabs(x-np) < 0.1*(x+np)) { |
| v = (x-np)/(x+np); // might underflow to 0 |
| s = (x-np)*v;/* s using v -- change by MM */ |
| if(fabs(s) < DBL_MIN) return s; |
| ej = 2*x*v; |
| v = v*v; |
| for (j = 1; j < 1000; j++) { /* Taylor series; 1000: no infinite loop |
| as |v| < .1, v^2000 is "zero" */ |
| ej *= v;// = v^(2j+1) |
| s1 = s+ej/((j<<1)+1); |
| if (s1 == s) /* last term was effectively 0 */ |
| return s1 ; |
| s = s1; |
| } |
| } |
| /* else: | x - np | is not too small */ |
| return(x*log(x/np)+np-x); |
| } |