The R Project SVN R

/*
 *  Mathlib : A C Library of Special Functions
 *  Copyright (C) 1998 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., 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 *  SYNOPSIS
 *
 *    #include "mathlib.h"
 *    double rt(double df);
 *
 *  DESCRIPTION
 *
 *    Pseudo-random variates from an F distribution.
 *
 *  NOTES
 *
 *    This function calls rchisq and rnorm to do the real work.
 */

#include "Mathlib.h"

double rt(double df)
{
    if (
#ifdef IEEE_754
    isnan(df) ||
#endif
    df <= 0.0) {
    ML_ERROR(ME_DOMAIN);
    }
    if(!finite(df))
    return snorm();
    else
    return snorm() / sqrt(rchisq(df) / df);
}