[texhax] strange behavior of amsmath

Herbert Voss Herbert.Voss at FU-Berlin.DE
Thu Dec 12 20:30:40 CET 2013

>> Le 12 déc. 2013 à 00:43, Reinhard Kotucha <reinhard.kotucha at web.de> a écrit :
>>
>>> Hi,
>>> I would expect that the fleqn option of amsmath has only an impact on
>>> horizontal glue.
>>>
>>> Curiously, if the fleqn option is active, there is extra vertical glue
>>> below the first formula of each paragraph and below the first formula
>>> following ordinary text.
>>>
>>> Here is a minimal example:
>>>
>>> <testfleqn.tex.gz>
>>> You get correct vertical spacing if you comment out the line
>>> containing "[fleqn]".  The relevant part of the amsmath source code
>>> looks quite innocent.  I can reproduce the problem with TeX Live 2003
>>> too, the oldest TL release I've currently installed.

I get correct vertical spacing without using the verbatim
environment. the first equation after the text has
\above|\belowdisplayskip and all others have
\above|\belowdisplayshortskip

\documentclass{minimal}
\usepackage
[fleqn]
{amsmath}

\begin{document}

equation
%
$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$
$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$
$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$
%
text
%
$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$
$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$
$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$
%
displaymath
%
\begin{displaymath}$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$\end{displaymath}
\begin{displaymath}$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$\end{displaymath}
\begin{displaymath}$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$\end{displaymath}
%
text
%
\begin{displaymath}$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$\end{displaymath}
\begin{displaymath}$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$\end{displaymath}
\begin{displaymath}$$\vartheta=2\pi\smash{\rule{.4pt}{4ex}}$$\end{displaymath}
%
\end{document}

Herbert