gcc/fortran/doc/gfortran/intrinsic-procedures/log.rst

   1 ..
   2   Copyright 1988-2022 Free Software Foundation, Inc.
   3   This is part of the GCC manual.
   4   For copying conditions, see the copyright.rst file.
   5
   6 .. _log:
   7
   8 .. index:: LOG
   9
  10 .. index:: ALOG
  11
  12 .. index:: DLOG
  13
  14 .. index:: CLOG
  15
  16 .. index:: ZLOG
  17
  18 .. index:: CDLOG
  19
  20 .. index:: exponential function, inverse
  21
  22 .. index:: logarithm function
  23
  24 .. index:: natural logarithm function
  25
  26 LOG --- Natural logarithm function
  27 **********************************
  28
  29 .. function:: LOG(X)
  30
  31   ``LOG(X)`` computes the natural logarithm of :samp:`{X}`, i.e. the
  32   logarithm to the base e.
  33
  34   :param X:
  35     The type shall be ``REAL`` or
  36     ``COMPLEX``.
  37
  38   :return:
  39     The return value is of type ``REAL`` or ``COMPLEX``.
  40     The kind type parameter is the same as :samp:`{X}`.
  41     If :samp:`{X}` is ``COMPLEX``, the imaginary part \omega is in the range
  42     -\pi < \omega \leq \pi.
  43
  44   Standard:
  45     Fortran 77 and later, has GNU extensions
  46
  47   Class:
  48     Elemental function
  49
  50   Syntax:
  51     .. code-block:: fortran
  52
  53       RESULT = LOG(X)
  54
  55   Example:
  56     .. code-block:: fortran
  57
  58       program test_log
  59         real(8) :: x = 2.7182818284590451_8
  60         complex :: z = (1.0, 2.0)
  61         x = log(x)    ! will yield (approximately) 1
  62         z = log(z)
  63       end program test_log
  64
  65   Specific names:
  66     .. list-table::
  67        :header-rows: 1
  68
  69        * - Name
  70          - Argument
  71          - Return type
  72          - Standard
  73
  74        * - ``ALOG(X)``
  75          - ``REAL(4) X``
  76          - ``REAL(4)``
  77          - Fortran 77 or later
  78        * - ``DLOG(X)``
  79          - ``REAL(8) X``
  80          - ``REAL(8)``
  81          - Fortran 77 or later
  82        * - ``CLOG(X)``
  83          - ``COMPLEX(4) X``
  84          - ``COMPLEX(4)``
  85          - Fortran 77 or later
  86        * - ``ZLOG(X)``
  87          - ``COMPLEX(8) X``
  88          - ``COMPLEX(8)``
  89          - GNU extension
  90        * - ``CDLOG(X)``
  91          - ``COMPLEX(8) X``
  92          - ``COMPLEX(8)``
  93          - GNU extension