gammap

double gammap(double x, double a, double b);

Returns the value of the Gamma random variable distribution function with alpha a and beta b at the value x.

Parameters:
xCritical point.
aAlpha shape parameter.
bBeta scale parameter.

Returns:
P(X ≤ x | a, b)

Errors:
NUMERICS_ERROR is raised if a ≤ 0 or b ≤ 0

Usage:
double p = gammap(.5, 1.5, 2.75)

Header:
#include "contdist.h"