From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.ciao.gmane.io!not-for-mail From: Mauro Aranda Newsgroups: gmane.emacs.bugs Subject: bug#41223: 28.0.50; Calc gives wrong determinant for some matrices with symbolic variables Date: Thu, 14 May 2020 08:41:40 -0300 Message-ID: References: <7A33094E-BD4C-45DE-A57D-F23D50CFC6B4@acm.org> Mime-Version: 1.0 Content-Type: multipart/alternative; boundary="000000000000d138a705a59a2ee4" Injection-Info: ciao.gmane.io; posting-host="ciao.gmane.io:159.69.161.202"; logging-data="51966"; mail-complaints-to="usenet@ciao.gmane.io" Cc: 41223@debbugs.gnu.org To: Mattias =?UTF-8?Q?Engdeg=C3=A5rd?= Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane-mx.org@gnu.org Thu May 14 13:42:12 2020 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jZCFf-000DQV-OQ for geb-bug-gnu-emacs@m.gmane-mx.org; 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charset="UTF-8" Content-Transfer-Encoding: quoted-printable Mattias Engdeg=C3=A5rd writes: > No doubt there are better ways of computing the determinant for > non-numeric matrices. In particular, division shouldn't be necessary > at all, and the current algorithm results in some untidy > expressions. For example, the determinant of > > [a 0 0 1] > [0 b 0 0] > [0 0 c 0] > [1 0 0 d] > > is given as abc*(d-1/a), falsely giving the impression of being > undefined for a=3D0, rather than bc(ad-1). I see. Yes, using a fraction-free algorithm would be good. But for the moment, getting bc(ad-1) as the result is one `j M' away. --000000000000d138a705a59a2ee4 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Mattias Engdeg=C3=A5rd <mattiase@acm.org> writes:

> No doubt there are better= ways of computing the determinant for
> non-numeric matrices. In par= ticular, division shouldn't be necessary
> at all, and the curren= t algorithm results in some untidy
> expressions. For example, the de= terminant of
>
> [a 0 0 1]
> [0 b 0 0]
> [0 0 c 0]<= br>> [1 0 0 d]
>
> is given as abc*(d-1/a), falsely giving t= he impression of being
> undefined for a=3D0, rather than bc(ad-1).
I see.=C2=A0 Yes, using a fraction-free algorithm would be good.=C2= =A0 But for the
moment, getting bc(ad-1) as the result is one `j M' = away.
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