From owner-sc22wg5@open-std.org Thu Oct 22 08:25:54 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 A6B47C76BB7; Thu, 22 Oct 2009 08:25:54 +0200 (CET DST) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from ironport1.lbl.gov (ironport1.lbl.gov [128.3.41.47]) by www2.open-std.org (Postfix) with ESMTP id E0F50C178E4 for ; Thu, 22 Oct 2009 08:25:50 +0200 (CET DST) X-Ironport-SBRS: None X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AvQAAOGX30pMfpWb/2dsb2JhbAAI2kSEPQQ X-IronPort-AV: E=Sophos;i="4.44,603,1249282800"; d="scan'208";a="124488958" Received: from c-76-126-149-155.hsd1.ca.comcast.net (HELO [192.168.1.103]) ([76.126.149.155]) by ironport1.lbl.gov with ESMTP/TLS/DHE-RSA-AES256-SHA; 21 Oct 2009 23:25:48 -0700 Message-ID: <4ADFFB02.40909@lbl.gov> Date: Wed, 21 Oct 2009 23:26:10 -0700 From: Aleksandar Donev User-Agent: Thunderbird 2.0.0.23 (Windows/20090812) MIME-Version: 1.0 To: SC22WG5 Subject: Re: (j3.2006) (SC22WG5.4105) [ukfortran] Standard intrinsics and coarrays 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> In-Reply-To: <20091022051613.0AEF5C178E4@www2.open-std.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-sc22wg5@open-std.org Precedence: bulk Malcolm Cohen wrote: > In a "shared" generator there is a single seed and a single sequence. > Images take values from that single sequence. Presumably if two calls to RANDOM_NUMBER are unordered, what order they take from the sequence is undefined. These kinds of things would need to be spelled out explicitly. > In a "separate" generator, each image has a seed and a sequence. Each > image takes values from its own sequence. Are the generators the same on each image (i.e., same sequence for the same seed)? Also needs to be spelled out explicitly. > Perhaps we should require that it should be one or the other. If we do the choice is obvious: separate generators on each image. Isn't there some room in-between. One can have separate streams but that get initialized during a call to RANDOM_SEED together so that they are independent on each image. Perhap's we should allow for such cases? For example, the SPRNG library (http://sprng.cs.fsu.edu/sprng.html) has a Modified Lagged Fibonacci Generator generator that: "The seed used during initialization for this generator does not move one to a different point in the sequence. Rather, it returns a different sequence. The seeding algorithms ensures that if the same seed is used for all the streams, then the streams obtained are independent. If a user initializes different streams with different seeds, then it is possible that the same sequence may be assigned to two different streams and hence we may no longer have independent streams. Thus it is important to use the same seed while initializing all the streams with this generator." Aleks