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Date: 22 Oct 2009 19:22:40 +0100
From: "N.M. Maclaren" <nmm1@cam.ac.uk>
To: SC22WG5 <sc22wg5@open-std.org>
Subject: Re: [ukfortran] (SC22WG5.4117) (j3.2006)  Parallel random numbers
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Precedence: bulk

Here is some alternative wording.  It says as little as possible, and most
of that is in a NOTE.  I really do think that being too specific is a bad
mistake, as this is not an area that is easy to make proof against future
developments.

    It is processor dependent whether RANDOM_SEED and RANDOM_NUMBER use
    a common generator for all images or whether each image uses a
    separate one.

    NOTE 13.x
    The range of possible implementations includes:
        * All images use a common generator, and those procedures are
    properly interlocked to make multiple calls in unordered segments
    work correctly.
        * Each image uses a separate copy of the same generator, with
    the same or a different default seed for all images.
        * Each image uses a different generator, possibly with true or
    quasi-independence of those generators.

[ And, yes, if you have suitable hardware support, true independence
is possible. ]

Plus edits to A2.

Regards,
Nick.