### 8.153 `LOG` — Natural logarithm function

Description:
  `LOG(X)` computes the natural logarithm of X, i.e. the logarithm to the base e.
Standard:
  Fortran 77 and later
Class:
  Elemental function
Syntax:
  `RESULT = LOG(X)`
Arguments:

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

Return value:
  The return value is of type `REAL` or `COMPLEX`. The kind type parameter is the same as X. If X is `COMPLEX`, the imaginary part \omega is in the range -\pi \leq \omega \leq \pi.
Example:

                program test_log
                  real(8) :: x = 2.7182818284590451_8
                  complex :: z = (1.0, 2.0)
                  x = log(x)    ! will yield (approximately) 1
                  z = log(z)
                end program test_log

Specific names:

  Name | Argument | Return type | Standard
  `ALOG(X)` | `REAL(4) X` | `REAL(4)` | f95, gnu
  `DLOG(X)` | `REAL(8) X` | `REAL(8)` | f95, gnu
  `CLOG(X)` | `COMPLEX(4) X` | `COMPLEX(4)` | f95, gnu
  `ZLOG(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | f95, gnu
  `CDLOG(X)` | `COMPLEX(8) X` | `COMPLEX(8)` | f95, gnu