gcc/fortran/doc/gfortran/intrinsic-procedures/srand.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 .. _srand:
   7
   8 SRAND --- Reinitialize the random number generator
   9 **************************************************
  10
  11 .. index:: SRAND, random number generation, seeding, seeding a random number generator
  12
  13 .. function:: SRAND(SEED)
  14
  15   ``SRAND`` reinitializes the pseudo-random number generator
  16   called by ``RAND`` and ``IRAND``. The new seed used by the
  17   generator is specified by the required argument :samp:`{SEED}`.
  18
  19   :param SEED:
  20     Shall be a scalar ``INTEGER(kind=4)``.
  21
  22   :return:
  23     Does not return anything.
  24
  25   Standard:
  26     GNU extension
  27
  28   Class:
  29     Subroutine
  30
  31   Syntax:
  32     .. code-block:: fortran
  33
  34       CALL SRAND(SEED)
  35
  36   Example:
  37     See ``RAND`` and ``IRAND`` for examples.
  38
  39   Notes:
  40     The Fortran standard specifies the intrinsic subroutines
  41     ``RANDOM_SEED`` to initialize the pseudo-random number
  42     generator and ``RANDOM_NUMBER`` to generate pseudo-random numbers.
  43     These subroutines should be used in new codes.
  44
  45     Please note that in GNU Fortran, these two sets of intrinsics (``RAND``,
  46     ``IRAND`` and ``SRAND`` on the one hand, ``RANDOM_NUMBER`` and
  47     ``RANDOM_SEED`` on the other hand) access two independent
  48     pseudo-random number generators.
  49
  50   See also:
  51     :ref:`RAND`,
  52     :ref:`RANDOM_SEED`,
  53     :ref:`RANDOM_NUMBER`