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/* cdf/fdist.c
*
* Copyright (C) 2002 Przemyslaw Sliwa and Jason H. Stover.
* Copyright (C) 2006 Brian Gough
*
* 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 <config.h>
#include <math.h>
#include <gsl/gsl_cdf.h>
#include <gsl/gsl_sf_gamma.h>
#include <gsl/gsl_math.h>
#include <gsl/gsl_errno.h>
#include "error.h"
#include "beta_inc.c"
/*
* Lower tail.
*/
double
gsl_cdf_fdist_P (const double x, const double nu1, const double nu2)
{
double P;
double r = nu2 / nu1;
if (x < r)
{
double u = x / (r + x);
P = beta_inc_AXPY (1.0, 0.0, nu1 / 2.0, nu2 / 2.0, u);
}
else
{
double u = r / (r + x);
P = beta_inc_AXPY (-1.0, 1.0, nu2 / 2.0, nu1 / 2.0, u);
}
return P;
}
/*
* Upper tail.
*/
double
gsl_cdf_fdist_Q (const double x, const double nu1, const double nu2)
{
double Q;
double r = nu2 / nu1;
if (x < r)
{
double u = x / (r + x);
Q = beta_inc_AXPY (-1.0, 1.0, nu1 / 2.0, nu2 / 2.0, u);
}
else
{
double u = r / (r + x);
Q = beta_inc_AXPY (1.0, 0.0, nu2 / 2.0, nu1 / 2.0, u);
}
return Q;
}
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