From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!not-for-mail From: Marius Vollmer Newsgroups: gmane.lisp.guile.bugs Subject: Re: generic * and 0 Date: Wed, 06 Dec 2006 17:52:43 +0200 Message-ID: <873b7tyqb8.fsf@zagadka.de> References: <456DCA43.6030705@ludens.elte.hu> <878xhr4cgj.fsf@zip.com.au> <66e540fe0612011222n42a0e62ai1250ff67ae801c93@mail.gmail.com> <87irgv2sj6.fsf@zip.com.au> <87zma433s7.fsf@zip.com.au> <66e540fe0612041026n3a6ca3f5ye46e775becdce611@mail.gmail.com> <87wt57ky8z.fsf@zip.com.au> NNTP-Posting-Host: dough.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Trace: sea.gmane.org 1165420394 12507 80.91.229.10 (6 Dec 2006 15:53:14 GMT) X-Complaints-To: usenet@sea.gmane.org NNTP-Posting-Date: Wed, 6 Dec 2006 15:53:14 +0000 (UTC) Cc: bug-guile@gnu.org Original-X-From: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Wed Dec 06 16:53:12 2006 Return-path: Envelope-to: guile-bugs@m.gmane.org Original-Received: from lists.gnu.org ([199.232.76.165]) by dough.gmane.org with esmtp (Exim 4.50) id 1Grz53-0006tU-3o for guile-bugs@m.gmane.org; Wed, 06 Dec 2006 16:53:09 +0100 Original-Received: from localhost ([127.0.0.1] helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Grz52-0004ff-Nt for guile-bugs@m.gmane.org; Wed, 06 Dec 2006 10:53:08 -0500 Original-Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Grz4K-0004IL-VB for bug-guile@gnu.org; Wed, 06 Dec 2006 10:52:25 -0500 Original-Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Grz4H-0004Fi-OC for bug-guile@gnu.org; Wed, 06 Dec 2006 10:52:24 -0500 Original-Received: from [199.232.76.173] (helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Grz4H-0004Fd-IU for bug-guile@gnu.org; Wed, 06 Dec 2006 10:52:21 -0500 Original-Received: from [213.243.153.39] (helo=smtp5.pp.htv.fi) by monty-python.gnu.org with esmtp (Exim 4.52) id 1Grz4H-00018I-Hu for bug-guile@gnu.org; Wed, 06 Dec 2006 10:52:21 -0500 Original-Received: from zagadka.ping.de (cs27004209.pp.htv.fi [89.27.4.209]) by smtp5.pp.htv.fi (Postfix) with SMTP id 64FE15BC186 for ; Wed, 6 Dec 2006 17:52:09 +0200 (EET) Original-Received: (qmail 24562 invoked by uid 1000); 6 Dec 2006 17:52:43 +0200 Original-To: Kevin Ryde In-Reply-To: <87wt57ky8z.fsf@zip.com.au> (Kevin Ryde's message of "Tue\, 05 Dec 2006 11\:00\:28 +1100") User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/23.0.0 (gnu/linux) X-BeenThere: bug-guile@gnu.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: "Bug reports for GUILE, GNU's Ubiquitous Extension Language" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Original-Sender: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Errors-To: bug-guile-bounces+guile-bugs=m.gmane.org@gnu.org Xref: news.gmane.org gmane.lisp.guile.bugs:3418 Archived-At: Kevin Ryde writes: > The only case I can think of where a common zero may not be good is > with matrices, where "(* 0 matrix) => matrix" could preserve the > dimensions of the input matrix in the output matrix. I would have to dig for the specifics (having forgotton most of my math by now), but 'scaling' matrices and 'multiplying' them are actually two different operations. They are unfortunately notated the same. (* scalar matrix) is scaling, and (* matrix matrix) is multiplying. A special case of this is the more familiar vector scaling versus the vector dot product, I think. Thus, it makes sense to me to let the 'unknown' object in a call to an arithmetic operation decide how to interpret it, and not doing any shortcuts. In general, it is not guaranteed that (* 0 something) is even well-defined, it might be an error. -- GPG: D5D4E405 - 2F9B BCCC 8527 692A 04E3 331E FAF8 226A D5D4 E405 _______________________________________________ Bug-guile mailing list Bug-guile@gnu.org http://lists.gnu.org/mailman/listinfo/bug-guile