gammaincc

constexpr double gammaincc(const double a, const double x) noexcept: Evaluates the upper incomplete gamma function [1].

Parameters

const double a

A real number.

const double x

A real number.

Returns

double

A real number.

The upper incomplete gamma function evaluates the upper portion of the gamma integral from \(x\) to \(\infty\). It is defined as:

\[\Gamma(a, x) = \int_{x}^{\infty} t^{x - 1}e^{-t}dt\]

Example

double a = 1;
double x = 1;
std::cout << gammaincc(a, x) << "\n";

Output:

0.367875

References