gcc/fortran/doc/gfortran/intrinsic-procedures/randominit.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 .. index:: RANDOM_INIT, random number generation, initialization
   7
   8 .. _random_init:
   9
  10 RANDOM_INIT --- Initialize a pseudo-random number generator
  11 ***********************************************************
  12
  13 .. function:: RANDOM_INIT(REPEATABLE, IMAGE_DISTINCT)
  14
  15   Initializes the state of the pseudorandom number generator used by
  16   ``RANDOM_NUMBER``.
  17
  18   :param REPEATABLE:
  19     Shall be a scalar with a ``LOGICAL`` type,
  20     and it is ``INTENT(IN)``.  If it is ``.true.``, the seed is set to
  21     a processor-dependent value that is the same each time ``RANDOM_INIT``
  22     is called from the same image.  The term 'same image' means a single
  23     instance of program execution.  The sequence of random numbers is different
  24     for repeated execution of the program.  If it is ``.false.``, the seed
  25     is set to a processor-dependent value.
  26
  27   :param IMAGE_DISTINCT:
  28     Shall be a scalar with a
  29     ``LOGICAL`` type, and it is ``INTENT(IN)``.  If it is ``.true.``,
  30     the seed is set to a processor-dependent value that is distinct from th
  31     seed set by a call to ``RANDOM_INIT`` in another image.  If it is
  32     ``.false.``, the seed is set to a value that does depend which image called
  33     ``RANDOM_INIT``.
  34
  35   Standard:
  36     Fortran 2018
  37
  38   Class:
  39     Subroutine
  40
  41   Syntax:
  42     .. code-block:: fortran
  43
  44       CALL RANDOM_INIT(REPEATABLE, IMAGE_DISTINCT)
  45
  46   Example:
  47     .. code-block:: fortran
  48
  49       program test_random_seed
  50         implicit none
  51         real x(3), y(3)
  52         call random_init(.true., .true.)
  53         call random_number(x)
  54         call random_init(.true., .true.)
  55         call random_number(y)
  56         ! x and y are the same sequence
  57         if (any(x /= y)) call abort
  58       end program test_random_seed
  59
  60   See also:
  61     :ref:`RANDOM_NUMBER`,
  62     :ref:`RANDOM_SEED`