[GiNaC-list] Bug report

Vladimir V. Kisil kisilv at maths.leeds.ac.uk
Fri Aug 24 00:30:57 CEST 2018


>>>>> On Thu, 23 Aug 2018 13:22:06 +0800 (GMT+08:00), 杨强  <acrobat at mail.ustc.edu.cn> said:

    > Dear all, I use GiNaC to perform analytic calculation, but when I
    > try to use .numer() and .denom() methods, I get a wrong result.

    > 1. expr.numer()/expr.denom() is not always equal to the original
    > expression!!!  2. Using .numer_denom() method could always get the
    > correct answer.

    It is not actually a bug. Since a/b = (-a)/(-b), numer() and denom()
  are only defined up to a sign. Thus their separate evaluation may lead
  to expr.numer()/expr.denom() with the opposite sign to expr.

  I am proposing a patch to tutorial reminding that,

  Best wishes,
Vladimir V. Kisil                 http://www.maths.leeds.ac.uk/~kisilv/
  Book:     Geometry of Mobius Transformations     http://goo.gl/EaG2Vu
  Software: Geometry of cycles          http://moebinv.sourceforge.net/

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