### 8.80 `EXP` — Exponential function

Description:
  `EXP(X)` computes the base e exponential of X.
Standard:
  Fortran 77 and later, has overloads that are GNU extensions
Class:
  Elemental function
Syntax:
  `RESULT = EXP(X)`
Arguments:

  X | The type shall be `REAL` or `COMPLEX`.

Return value:
  The return value has same type and kind as X.
Example:

                program test_exp
                  real :: x = 1.0
                  x = exp(x)
                end program test_exp

Specific names:

  Name | Argument | Return type | Standard
  `EXP(X)` | `REAL(4) X` | `REAL(4)` | Fortran 77 and later
  `DEXP(X)` | `REAL(8) X` | `REAL(8)` | Fortran 77 and later
  `CEXP(X)` | `COMPLEX(4) X` | `COMPLEX(4)` | Fortran 77 and later
  `ZEXP(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | GNU extension
  `CDEXP(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | GNU extension