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/* gdtr.c
*
* Gamma distribution function
*
*
*
* SYNOPSIS:
*
* double a, b, x, y, gdtr();
*
* y = gdtr( a, b, x );
*
*
*
* DESCRIPTION:
*
* Returns the integral from zero to x of the Gamma probability
* density function:
*
*
* x
* b -
* a | | b-1 -at
* y = ----- | t e dt
* - | |
* | (b) -
* 0
*
* The incomplete Gamma integral is used, according to the
* relation
*
* y = igam( b, ax ).
*
*
* ACCURACY:
*
* See igam().
*
* ERROR MESSAGES:
*
* message condition value returned
* gdtr domain x < 0 0.0
*
*/
/* gdtrc.c
*
* Complemented Gamma distribution function
*
*
*
* SYNOPSIS:
*
* double a, b, x, y, gdtrc();
*
* y = gdtrc( a, b, x );
*
*
*
* DESCRIPTION:
*
* Returns the integral from x to infinity of the Gamma
* probability density function:
*
*
* inf.
* b -
* a | | b-1 -at
* y = ----- | t e dt
* - | |
* | (b) -
* x
*
* The incomplete Gamma integral is used, according to the
* relation
*
* y = igamc( b, ax ).
*
*
* ACCURACY:
*
* See igamc().
*
* ERROR MESSAGES:
*
* message condition value returned
* gdtrc domain x < 0 0.0
*
*/
/* gdtr() */
/*
* Cephes Math Library Release 2.3: March,1995
* Copyright 1984, 1987, 1995 by Stephen L. Moshier
*/
#include "mconf.h"
double gdtri(double, double, double);
double gdtr(a, b, x)
double a, b, x;
{
if (x < 0.0) {
mtherr("gdtr", DOMAIN);
return (NPY_NAN);
}
return (igam(b, a * x));
}
double gdtrc(a, b, x)
double a, b, x;
{
if (x < 0.0) {
mtherr("gdtrc", DOMAIN);
return (NPY_NAN);
}
return (igamc(b, a * x));
}
double gdtri(a, b, y)
double a, b, y;
{
if ((y < 0.0) || (y > 1.0) || (a <= 0.0) || (b < 0.0)) {
mtherr("gdtri", DOMAIN);
return (NPY_NAN);
}
return (igamci(b, 1.0 - y) / a);
}
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