What is "gamma function"

n. (context analysis English) A mathematical function which generalizes the notion of a factorial, taking any real value as input.

To read about gamma distribution, see Gamma distribution

In mathematics, the gamma function (represented by the capital Greek letter ) is an extension of the factorial function, with its argument shifted down by 1, to real and complex numbers. That is, if is a positive integer:

Γ(n) = (n − 1)!
.

The gamma function is defined for all complex numbers except the non-positive integers. For complex numbers with a positive real part, it is defined via a convergent improper integral:

Γ(t) = ∫xe dx
.

This integral function is extended by analytic continuation to all complex numbers except the non-positive integers (where the function has simple poles), yielding the meromorphic function we call the gamma function. In fact the gamma function corresponds to the Mellin transform of the negative exponential function:

$$\Gamma(t) = \{ \mathcal M e^{-x} \} (t)$$
.

The gamma function is a component in various probability-distribution functions, and as such it is applicable in the fields of probability and statistics, as well as combinatorics.