From owner-sc22wg5@open-std.org Thu Oct 22 20:22:42 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 021A8C76BC4; Thu, 22 Oct 2009 20:22:42 +0200 (CET DST) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from ppsw-0.csi.cam.ac.uk (ppsw-0.csi.cam.ac.uk [131.111.8.130]) by www2.open-std.org (Postfix) with ESMTP id 7432DC178E4 for ; Thu, 22 Oct 2009 20:22:40 +0200 (CET DST) X-Cam-AntiVirus: no malware found X-Cam-SpamDetails: not scanned X-Cam-ScannerInfo: http://www.cam.ac.uk/cs/email/scanner/ Received: from hermes-1.csi.cam.ac.uk ([131.111.8.51]:52892) by ppsw-0.csi.cam.ac.uk (smtp.hermes.cam.ac.uk [131.111.8.150]:25) with esmtpa (EXTERNAL:nmm1) id 1N12J6-0005kE-19 (Exim 4.70) for sc22wg5@open-std.org (return-path ); Thu, 22 Oct 2009 19:22:40 +0100 Received: from prayer by hermes-1.csi.cam.ac.uk (hermes.cam.ac.uk) with local (PRAYER:nmm1) id 1N12J6-0001gI-B4 (Exim 4.67) for sc22wg5@open-std.org (return-path ); Thu, 22 Oct 2009 19:22:40 +0100 Received: from [83.67.89.123] by webmail.hermes.cam.ac.uk with HTTP (Prayer-1.3.2); 22 Oct 2009 19:22:40 +0100 Date: 22 Oct 2009 19:22:40 +0100 From: "N.M. Maclaren" To: SC22WG5 Subject: Re: [ukfortran] (SC22WG5.4117) (j3.2006) Parallel random numbers Message-ID: In-Reply-To: <20091022180052.C139DC178E4@www2.open-std.org> 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> X-Mailer: Prayer v1.3.2 Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset=ISO-8859-1 Sender: owner-sc22wg5@open-std.org 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.