[GiNaC-devel] Sqrfree_parfrac Issue GiNaC

[Vladimir V. Kisil]

Dear All,

I have attempted to add some more tests for sqrfree_parfrac() and it turned out that GiNaC crashes on x*(x^2-1)^(-1) with

terminate called after throwing an instance of 'std::runtime_error'
  what():  matrix::solve(): inconsistent linear system

Thus some further investigation is required in this routine.

Best wishes,
Vladimir

________________________________________
From: Vladimir V. Kisil <V.Kisil at leeds.ac.uk>
Sent: 23 July 2020 23:08
To: GiNaC-devel List
Cc: vittorio del duca; Claude Duhr; ginac-list at ginac.de; Konstantin Leyde; Vladimir V. Kisil
Subject: Re: Sqrfree_parfrac Issue GiNaC

Dear Konstantin,

Many thanks for reporting the bug with a detailed description. I am attaching a patch to fix it.

Best wishes,
Vladimir
--
Vladimir V. Kisil                 http://www.maths.leeds.ac.uk/~kisilv/
  Book:      Geometry of Mobius Maps       https://doi.org/10.1142/p835
  Soft:      Geometry of cycles         http://moebinv.sourceforge.net/
  Jupyter notebooks:       https://github.com/vvkisil/MoebInv-notebooks
________________________________________
From: GiNaC-list <ginac-list-bounces at ginac.de> on behalf of Konstantin Leyde <konstantin.leyde at live.com>
Sent: 22 July 2020 19:16
To: ginac-list at ginac.de
Cc: vittorio del duca; Claude Duhr
Subject: [GiNaC-list] Sqrfree_parfrac Issue GiNaC

Hello,

My name is Konstantin Leyde, and I am a master student in physics at the ETH Zurich.

For my thesis project, I have been working with the GiNaC library, and I have encountered an issue with the partial fractioning (sqrfree_parfrac) routine:
Unless I misunderstood the way the sqrfree_parfrac routine works, it appears that for special cases, the output of the sqrfree_parfrac routine misses a numerical prefactor for one term, and thus returns the wrong answer.

Please find attached a pdf, that explains the problem in more detail.
In this pdf (as well as separately) we have attached the code that shows the issue.


Many thanks in advance,

Best wishes,
Konstantin