From owner-sc22wg5@open-std.org Thu Oct 22 23:21:49 2009 Return-Path: X-Original-To: sc22wg5-dom8 Delivered-To: sc22wg5-dom8@www2.open-std.org Received: by www2.open-std.org (Postfix, from userid 521) id 911A1C76BC4; Thu, 22 Oct 2009 23:21:49 +0200 (CET DST) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from mail1.cray.com (mail1.cray.com [136.162.62.100]) by www2.open-std.org (Postfix) with ESMTP id AD6C7C76BB7 for ; Thu, 22 Oct 2009 23:21:47 +0200 (CET DST) Received: from beaver.us.cray.com (beaver.us.cray.com [172.30.74.51]) by mail1.cray.com (8.13.6/8.13.3/gw-5323) with ESMTP id n9MLLibL001545 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=FAIL); Thu, 22 Oct 2009 16:21:44 -0500 (CDT) Received: from cfexcas01.americas.cray.com (cfexcas01-2.us.cray.com [172.30.74.227]) by beaver.us.cray.com (8.13.8/8.13.3/hub-5273) with ESMTP id n9MLLhcP030226; Thu, 22 Oct 2009 16:21:43 -0500 Received: from fortran.us.cray.com (172.31.19.200) by cfexcas01.americas.cray.com (172.30.74.226) with Microsoft SMTP Server (TLS) id 8.1.393.1; Thu, 22 Oct 2009 16:21:42 -0500 Message-ID: <4AE0CD00.1000502@cray.com> Date: Thu, 22 Oct 2009 16:22:08 -0500 From: Bill Long Reply-To: Organization: Cray Inc. User-Agent: Thunderbird 2.0.0.23 (Macintosh/20090812) MIME-Version: 1.0 To: fortran standards email list for J3 Cc: SC22WG5 Subject: Re: (j3.2006) (SC22WG5.4118) [ukfortran] Parallel random numbers References: <20091020111544.C0F5CC178E3@www2.open-std.org> <20091022160201.90187C76BB7@www2.open-std.org> <20091022172236.755B9C76BB7@www2.open-std.org> <20091022180052.C139DC178E4@www2.open-std.org> <20091022182242.311F0C178E4@www2.open-std.org> In-Reply-To: <20091022182242.311F0C178E4@www2.open-std.org> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Cray-VirusStatus: clean Sender: owner-sc22wg5@open-std.org Precedence: bulk N.M. Maclaren wrote: > 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. The word "common" might be misinterpreted as "same algorithm" or even "ordinary". Maybe "shared" would be better. This seems sufficiently vague to be backward compatible with F03 and any current implementation. We typically discuss in normative text results of execution, rather than the method of computing the results. Maybe the whole bit should be a NOTE in the RANDOM_NUMBER subclause. Or maybe word this as "It is processor dependent whether the sequence of values returned by RANDOM_NUMBER is separate for each image, or is taken from a shared sequence. If separate, then calls to RANDOM_SEED affect only the sequence on the same image." [Wording could use some polish, but you get the idea...] Cheers, Bill > > 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. > > _______________________________________________ > J3 mailing list > J3@j3-fortran.org > http://j3-fortran.org/mailman/listinfo/j3 -- Bill Long longb@cray.com Fortran Technical Support & voice: 651-605-9024 Bioinformatics Software Development fax: 651-605-9142 Cray Inc., 1340 Mendota Heights Rd., Mendota Heights, MN, 55120