[texhax] strange behavior of amsmath
jfbu at free.fr
Thu Dec 12 09:04:33 CET 2013
Le 12 déc. 2013 à 00:43, Reinhard Kotucha <reinhard.kotucha at web.de> a écrit :
> 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:
> 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.
> The vertical bar in the test file is an argument of \smash, hence
> both, its height and depth is zero. Its sole purpose is to make the
> extra glue more visible.
> Please also note that "some text" in the test file doesn't start a new
> Where does the extra vertical space come from? I doubt that it's
Examining the log with showoutput reveals that with [fleqn] the first
formulas use of each block uses \abovedisplayskip and \belowdisplayskip
and the others \abovedisplayshortskip and \belowdisplayshortskip,
whereas without [fleqn] all use \abovedisplayshortskip and \belowdisplayshortskip
at least this is the probable location of the extra vertical glue, then
I have not looked at the amsmath code yet to find the spot where this
is is decided,
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