# Gamma

Advanced Analysis Library Only

double Gamma (double x, double *a);

## Purpose

Evaluates the gamma function or the incomplete gamma function, depending on the value of a. The gamma function is defined as follows:

The incomplete gamma function is defined as follows:

The following formula relates the gamma function to the factorial function:

## Parameters

Input
Name | Type | Description
x | double-precision | The point at which the gamma function is evaluated.
a | double-precision pointer | The upper limit of the incomplete gamma function. The gamma function is evaluated if a is NULL. Otherwise, the incomplete gamma function is evaluated.

## Return Value

Name | Type | Description
result | double-precision | The value of the evaluated gamma or incomplete gamma function.