/* cdf/cdf_gamma.c

 * 

 * Copyright (C) 2003 Jason Stover.

 * 

 * 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 3 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.

 */

/* 

 * Author: J. Stover

 */

#include <config.h>

#include <math.h>

#include <gsl/gsl_cdf.h>

#include <gsl/gsl_math.h>

#include <gsl/gsl_sf_gamma.h>

double

gsl_cdf_gamma_P (const double x, const double a, const double b)

{

  double P;

  double y = x / b;

  if (x <= 0.0)

    {

      return 0.0;

    }

  if (y > a)

    {

      P = 1 - gsl_sf_gamma_inc_Q (a, y);

    }

  else

    {

      P = gsl_sf_gamma_inc_P (a, y);

    }

  return P;

}

double

gsl_cdf_gamma_Q (const double x, const double a, const double b)

{

  double Q;

  double y = x / b;

  if (x <= 0.0)

    {

      return 1.0;

    }

  if (y < a)

    {

      Q = 1 - gsl_sf_gamma_inc_P (a, y);

    }

  else

    {

      Q = gsl_sf_gamma_inc_Q (a, y);

    }

  return Q;

}