Hi,
>>>>> On Thu, 23 Aug 2018 13:22:06 +0800 (GMT+08:00), 杨强 <acrobat(a)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
--
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/