GNU bug report logs - #41223
28.0.50; Calc gives wrong determinant for some matrices with symbolic variables

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Package: emacs;

Reported by: Mauro Aranda <maurooaranda <at> gmail.com>

Date: Tue, 12 May 2020 23:26:02 UTC

Severity: normal

Found in version 28.0.50

Done: Mattias Engdegård <mattiase <at> acm.org>

Bug is archived. No further changes may be made.

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Message #16 received at 41223-done <at> debbugs.gnu.org (full text, mbox):

From: Mattias Engdegård <mattiase <at> acm.org>
To: Mauro Aranda <maurooaranda <at> gmail.com>
Cc: 41223-done <at> debbugs.gnu.org
Subject: Re: bug#41223: 28.0.50; Calc gives wrong determinant for some
 matrices with symbolic variables
Date: Thu, 14 May 2020 10:43:19 +0200

14 maj 2020 kl. 00.15 skrev Mauro Aranda <maurooaranda <at> gmail.com>:

> It is good enough for me.  Thanks.

The pleasure was all mine! It has now been pushed to master.

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=0, rather than bc(ad-1).
This bug report was last modified 5 years and 11 days ago.

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