From owner-sc22wg5@open-std.org Thu Oct 22 08:23:14 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 28324C76BB7; Thu, 22 Oct 2009 08:23:14 +0200 (CET DST) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from ns.nag-j.co.jp (218-42-159-107.cust.bit-drive.ne.jp [218.42.159.107]) by www2.open-std.org (Postfix) with ESMTP id DC3BCC178E4 for ; Thu, 22 Oct 2009 08:23:10 +0200 (CET DST) Received: from 218-42-159-108.cust.bit-drive.ne.jp ([218.42.159.108] helo=Marucomputer) by ns.nag-j.co.jp with smtp (Exim 4.50) id 1N0r3O-0003eI-Up for sc22wg5@open-std.org; Thu, 22 Oct 2009 15:21:42 +0900 Message-ID: From: "Malcolm Cohen" To: "WG5" References: <20091020111544.C0F5CC178E3@www2.open-std.org><20091020154252.946EAC178E3@www2.open-std.org><20091021161933.1B2FCC178E3@www2.open-std.org><20091021171501.21FA4C178E3@www2.open-std.org><20091021175702.E4D26C178E3@www2.open-std.org> <20091022043326.83DB9C178E4@www2.open-std.org><20091022051613.0AEF5C178E4@www2.open-std.org> <20091022054551.77C95C178E4@www2.open-std.org> In-Reply-To: <20091022054551.77C95C178E4@www2.open-std.org> Subject: Re: [ukfortran] (SC22WG5.4106) (j3.2006) Standard intrinsics and coarrays Date: Thu, 22 Oct 2009 15:23:33 +0900 Organization: ??NAG MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response Content-Transfer-Encoding: 7bit X-Priority: 3 X-MSMail-Priority: Normal Importance: Normal X-Mailer: Microsoft Windows Live Mail 14.0.8089.726 X-MimeOLE: Produced By Microsoft MimeOLE V14.0.8089.726 Sender: owner-sc22wg5@open-std.org Precedence: bulk Nick wrote: >>> It is processor dependent whether all images use a common >>> generator or whether each image uses a separate one. I wrote: >> Perhaps we should require that it should be one or the other. Van wrote: > If we require a single generator, I meant exactly that we should require it to be "one or the other", not that we should pick which one ourselves. > If we require a single generator, it's difficult to get the same sequence on a > particular image on consecutive runs, which is useful (some would say > indispensible) for debogging, Unless the generation of random numbers on each image is independent of the results of the calculations or the speeds thereof on other images, it's impossible anyway. So you're going to be stuck in the bog. > It looks like Hobson's choice, but we ought either to choose, to provide a > mechanism for a program to choose, or require the processor to provide a > mechanism, outside the language, to choose. If the user desperately needs one or the other, he probably also needs various guarantees which we don't make about RANDOM_NUMBER (e.g. a lack of correlation between the sequences on each image) so will be using his own anyway. Depending on what he is doing, the qualities he wants from a PRNG will be different, and some of those qualities are mutually incompatible. I see no reason to punish the ordinary user by requiring a suboptimal choice of RANDOM_NUMBER on one subset of machines. Processor dependent is the right choice for the ordinary user, and the expert (or the person who needs an expert) will just have to read the manual or use a third-party product. Cheers, -- ................................Malcolm Cohen, Nihon NAG, Tokyo.