From owner-sc22wg5+sc22wg5-dom8=www.open-std.org@open-std.org Sat Mar 30 10:18:39 2013 Return-Path: X-Original-To: sc22wg5-dom8 Delivered-To: sc22wg5-dom8@www.open-std.org Received: by www.open-std.org (Postfix, from userid 521) id 08D0A356DC4; Sat, 30 Mar 2013 10:18:38 +0100 (CET) Delivered-To: sc22wg5@open-std.org Received: from ppsw-42.csi.cam.ac.uk (ppsw-42.csi.cam.ac.uk [131.111.8.142]) by www.open-std.org (Postfix) with ESMTP id 8D1EC3568DC for ; Sat, 30 Mar 2013 10:18:33 +0100 (CET) X-Cam-AntiVirus: no malware found X-Cam-ScannerInfo: http://www.cam.ac.uk/cs/email/scanner/ Received: from hermes-1.csi.cam.ac.uk ([131.111.8.51]:46943) by ppsw-42.csi.cam.ac.uk (smtp.hermes.cam.ac.uk [131.111.8.159]:25) with esmtpa (EXTERNAL:nmm1) id 1ULrvl-0002Qo-75 (Exim 4.80_167-5a66dd3) (return-path ); Sat, 30 Mar 2013 09:18:33 +0000 Received: from prayer by hermes-1.csi.cam.ac.uk (hermes.cam.ac.uk) with local (PRAYER:nmm1) id 1ULrvl-00056o-5c (Exim 4.72) (return-path ); Sat, 30 Mar 2013 09:18:33 +0000 Received: from [87.115.144.83] by webmail.hermes.cam.ac.uk with HTTP (Prayer-1.3.5); 30 Mar 2013 09:18:33 +0000 Date: 30 Mar 2013 09:18:33 +0000 From: "N.M. Maclaren" To: sc22wg5 Subject: Re: [ukfortran] (SC22WG5.4946) (j3.2006) AW: WG5 ballot on first draft TS 18508, Additional Parallel Features in Fortran (Update) Message-ID: In-Reply-To: <20130329232930.A368A356DC2@www.open-std.org> References: <20130329104945.2C28A356BB3@www.open-std.org> <20130329232930.A368A356DC2@www.open-std.org> X-Mailer: Prayer v1.3.5 Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset=ISO-8859-1 Sender: owner-sc22wg5@open-std.org Precedence: bulk On Mar 29 2013, Bill Long wrote: > >If we added this, it would be CO_PRODUCT since the local one is PRODUCT. > The previous proposal had CO_PRODUCT. It was removed because the >corresponding MPI_REDUCE for that operation almost never occurs in real >codes. Is there any common usage of this operation? Also, is there >hardware support in network hardware for a multiply reduction? Yes. It's a common reduction in anything that uses statistical models, especially generalised linear ones (by which I mean the original and general form, as formalised by John Nelder et al.) The point is that likelihoods multiply. And, of course, statistics includes information theory in this context (or conversely, if you prefer). There is no support in most hardware for most reductions or, indeed, most of modern Fortran. We shouldn't be adopting a C/C++ mindset and imagining that the primary purpose of a high-level language is to give the programmer access to the hardware facilities. Fortran has lasted over more variations in those than most people can believe! Regards, Nick Maclaren.