From a5d43a63a61816980138737931155362a68cd40a Mon Sep 17 00:00:00 2001 From: "Vladimir V. Kisil" Date: Thu, 23 Aug 2018 23:22:08 +0100 Subject: [PATCH] Explaining in tutorial sign ambiguity for numer() and denom() For example, for x/(x^2-1 independent evaluation of numer()} may returns x and denom() produces 1-x^2. Signed-off-by: Vladimir V. Kisil --- doc/tutorial/ginac.texi | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/doc/tutorial/ginac.texi b/doc/tutorial/ginac.texi index 3742567e..4306d227 100644 --- a/doc/tutorial/ginac.texi +++ b/doc/tutorial/ginac.texi @@ -5499,8 +5499,12 @@ 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 you have to 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 disagreed +signs of expressions, e.g. for $x/(x^2-1$ @code{numer()} returns $x$ and +and @code{denom()} produces $1-x^2$. @subsection Converting to a polynomial or rational expression -- 2.18.0