The R Project SVN R

/*

 *  R : A Computer Language for Statistical Data Analysis

 *  Copyright (C) 1995, 1996  Robert Gentleman and Ross Ihaka

 *  Copyright (C) 2000 The R Development 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

 *  http://www.r-project.org/Licenses/

 */

#include "nmath.h"

#include "dpq.h"

double dlogis(double x, double location, double scale, int give_log)

{

    double e, f;

#ifdef IEEE_754

    if (ISNAN(x) || ISNAN(location) || ISNAN(scale))

	return x + location + scale;

#endif

    if (scale <= 0.0)

	ML_ERR_return_NAN;

    x = fabs((x - location) / scale);

    e = exp(-x);

    f = 1.0 + e;

    return give_log ? -(x + log(scale * f * f)) : e / (scale * f * f);

}