From: Richard Kreckel <kreckel@ginac.de>
Date: Thu, 4 Oct 2018 19:28:42 +0000 (+0200)
Subject: [DOC] Explaining in tutorial sign ambiguity for numer() and denom().
X-Git-Tag: release_1-7-5~6
X-Git-Url: https://www.ginac.de/ginac.git//ginac.git?p=ginac.git;a=commitdiff_plain;h=1109fafaa3f5da6d1483744c4bdee6f01a37c5c5

[DOC] Explaining in tutorial sign ambiguity for numer() and denom().

Based on a patch provided by Vladimir V. Kisil <kisilv@maths.leeds.ac.uk>.
---

diff --git a/doc/tutorial/ginac.texi b/doc/tutorial/ginac.texi
index 3742567e..6e4ecb4b 100644
--- a/doc/tutorial/ginac.texi
+++ b/doc/tutorial/ginac.texi
@@ -5499,8 +5499,11 @@ ex ex::numer_denom();
 
 These functions will first normalize the expression as described above and
 then return the numerator, denominator, or both as a list, respectively.
-If you need both numerator and denominator, calling @code{numer_denom()} is
-faster than using @code{numer()} and @code{denom()} separately.
+If you need both numerator and denominator, call @code{numer_denom()}: it
+is faster than using @code{numer()} and @code{denom()} separately. And even
+more important: a separate evaluation of @code{numer()} and @code{denom()}
+may result in a spurious sign, e.g. for $x/(x^2-1)$ @code{numer()} may
+return $x$ and @code{denom()} $1-x^2$.
 
 
 @subsection Converting to a polynomial or rational expression