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

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From: Mauro Aranda <maurooaranda <at> gmail.com>
To: Mattias Engdegård <mattiase <at> acm.org>
Cc: 41223 <at> debbugs.gnu.org
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

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Mattias Engdegård <mattiase <at> acm.org> 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=0, 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.

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