From owner-sc22wg5@open-std.org Thu Oct 22 06:33:26 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 15603C76BB7; Thu, 22 Oct 2009 06:33:26 +0200 (CET DST) X-Original-To: sc22wg5@open-std.org Delivered-To: sc22wg5@open-std.org Received: from ironport2.lbl.gov (ironport2.lbl.gov [128.3.41.14]) by www2.open-std.org (Postfix) with ESMTP id 36F22C178E4 for ; Thu, 22 Oct 2009 06:33:24 +0200 (CET DST) X-Ironport-SBRS: None X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AvQAAJd930pMfpWb/2dsb2JhbAAIywYJjyYCglKBaQQ X-IronPort-AV: E=Sophos;i="4.44,602,1249282800"; d="scan'208";a="103616443" Received: from c-76-126-149-155.hsd1.ca.comcast.net (HELO [192.168.1.104]) ([76.126.149.155]) by ironport2.lbl.gov with ESMTP/TLS/DHE-RSA-AES256-SHA; 21 Oct 2009 21:33:22 -0700 Message-ID: <4ADFE090.4050604@lbl.gov> Date: Wed, 21 Oct 2009 21:33:20 -0700 From: Aleksandar Donev Organization: Lawrence Berkeley National Laboratory User-Agent: Thunderbird 2.0.0.23 (Windows/20090812) MIME-Version: 1.0 Cc: WG5 Subject: Re: (j3.2006) (SC22WG5.4101) [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> In-Reply-To: <20091021175702.E4D26C178E3@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 On 10/21/2009 10:57 AM, N.M. Maclaren wrote: > It is processor dependent whether all images use a common > generator or whether each image uses a separate one. What exactly does this mean? I get the feeling, but I believe we need to be more specific. The description of RANDOM_SEED is pretty specific about what is guaranteed, what is processor dependent, etc. For example, "When the values differ, the use of either value as the PUT argument in a subsequent call to RANDOM SEED shall result in the same sequence of pseudorandom numbers being generated." For the case of "separate" generators, it is clear, for the most part, since it follows the existing rules independently on each image. But we need to say more. What if all images supply the same PUT argument to RANDOM_SEED. Are they guaranteed to get the same sequence if they call RANDOM_NUMBER in unison? Or not? If the generators are truly independent, why should there be any restriction on ordering between RANDOM_SEED and RANDOM_NUMBER? In the case of a "shared" generator, I am not sure I understand exactly what is meant, guaranteed, or processor dependent. Is it obvious to others and I am just being dense? Thanks, Aleks -- Aleksandar Donev, Ph.D. Luis W. Alvarez Postdoctoral Fellow Center for Computational Sciences and Engineering (https://ccse.lbl.gov) Lawrence Berkeley National Laboratory (http://www.lbl.gov) E-mail: adonev@lbl.gov Phone: (510) 486-5782 Fax: (510) 486-6900 Address: MS 50A-1148, LBL, 1 Cyclotron Rd., Berkeley, CA 94720 Web: http://cims.nyu.edu/~donev/