The R Project SVN R

/*
 *  R : A Computer Language for Statistical Data Analysis
 *  Copyright (C) 1995, 1996  Robert Gentleman and Ross Ihaka
 *
 *  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, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA.
 */

#include "Mathlib.h"

double plogis(double x, double location, double scale)
{
#ifdef IEEE_754
    if (ISNAN(x) || ISNAN(location) || ISNAN(scale))
        return x + location + scale;
#endif
    if (scale <= 0.0) {
        ML_ERROR(ME_DOMAIN);
        return ML_NAN;
    }
    if(!R_FINITE(x)) {
        if (x > 0) return 1;
        else return 0;
    }
    return 1.0 / (1.0 + exp(-(x - location) / scale));
}