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From: Mauro Aranda <maurooaranda@gmail.com>
To: "Mattias Engdegård" <mattiase@acm.org>
Cc: 41223@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	[thread overview]
Message-ID: <CABczVwemMQiq3UaTnB54gV-FxN2vmjmiwD-Hv9PSeN__KzN+-A@mail.gmail.com> (raw)
In-Reply-To: <7A33094E-BD4C-45DE-A57D-F23D50CFC6B4@acm.org>

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Mattias Engdegård <mattiase@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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      parent reply	other threads:[~2020-05-14 11:41 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-12 23:24 bug#41223: 28.0.50; Calc gives wrong determinant for some matrices with symbolic variables Mauro Aranda
2020-05-13 12:58 ` Mattias Engdegård
2020-05-13 22:15   ` Mauro Aranda
2020-05-14  8:43     ` Mattias Engdegård
2020-05-14  9:56       ` Mattias Engdegård
2020-05-14 11:49         ` Mauro Aranda
2020-05-14 11:41       ` Mauro Aranda [this message]

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