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### 8.96 `GAMMA` — Gamma function

Description:
  `GAMMA(X)` computes Gamma (\Gamma) of X. For positive, integer values of X the Gamma function simplifies to the factorial function \Gamma(x)=(x-1)!.
Standard:
  Fortran 2008 and later
Class:
  Elemental function
Syntax:
  `X = GAMMA(X)`
Arguments:

  X | Shall be of type `REAL` and neither zero nor a negative integer.

Return value:
  The return value is of type `REAL` of the same kind as X.
Example:

                program test_gamma
                  real :: x = 1.0
                  x = gamma(x) ! returns 1.0
                end program test_gamma

Specific names:

  Name | Argument | Return type | Standard
  `GAMMA(X)` | `REAL(4) X` | `REAL(4)` | GNU Extension
  `DGAMMA(X)` | `REAL(8) X` | `REAL(8)` | GNU Extension

See also:
  Logarithm of the Gamma function: LOG_GAMMA