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[thirdparty/gcc.git] / gcc / fortran / doc / gfortran / intrinsic-procedures / randomseed.rst

..
  Copyright 1988-2022 Free Software Foundation, Inc.
  This is part of the GCC manual.
  For copying conditions, see the copyright.rst file.

.. index:: RANDOM_SEED, random number generation, seeding, seeding a random number generator

.. _random_seed:

RANDOM_SEED --- Initialize a pseudo-random number sequence
**********************************************************

.. function:: RANDOM_SEED(SIZE, PUT, GET)

  Restarts or queries the state of the pseudorandom number generator used by
  ``RANDOM_NUMBER``.

  :param SIZE:
    (Optional) Shall be a scalar and of type default
    ``INTEGER``, with ``INTENT(OUT)``. It specifies the minimum size
    of the arrays used with the :samp:`{PUT}` and :samp:`{GET}` arguments.

  :param PUT:
    (Optional) Shall be an array of type default
    ``INTEGER`` and rank one. It is ``INTENT(IN)`` and the size of
    the array must be larger than or equal to the number returned by the
    :samp:`{SIZE}` argument.

  :param GET:
    (Optional) Shall be an array of type default
    ``INTEGER`` and rank one. It is ``INTENT(OUT)`` and the size
    of the array must be larger than or equal to the number returned by
    the :samp:`{SIZE}` argument.

  Standard:
    Fortran 90 and later

  Class:
    Subroutine

  Syntax:
    .. code-block:: fortran

      CALL RANDOM_SEED([SIZE, PUT, GET])

  Example:
    .. code-block:: fortran

      program test_random_seed
        implicit none
        integer, allocatable :: seed(:)
        integer :: n

        call random_seed(size = n)
        allocate(seed(n))
        call random_seed(get=seed)
        write (*, *) seed
      end program test_random_seed

  See also:
    :ref:`RANDOM_NUMBER`,
    :ref:`RANDOM_INIT`