3.5.2.4.3.2 Incgamma

Definition

This function is used to calculate the incomplete Gamma function at x, with parameter a, which is denoted by: incgamma\left( a, x\right)=P\left( a, x\right)=\frac{1}{\Gamma \left( a\right)}\int _0^x t^{a-1}e^{-t}\,dt

where \Gamma (a) is the value of Gamma function at a. The parameters, a and x satisfy: a > 0 and x ≥ 0.

Syntax

double incgamma(double a, double x)

Parameters

a (input, double)

The argument a of the function. Constraint: a > 0.

x (input, double)

The argument x of the function. Constraint: x ≥ 0.

Return

Returns the value of the incomplete Gamma function at x, with parameter a.

Example

aa = incgamma(1, 5);
aa = ; //0.99326205300093

See Also

Gamma