# How to remove unnecessary space after flalign* environment

I was wondering whether it would be possible to remove some unnecessary space after flalign* environment. I tried using \belowdisplayskip, but to no avail.

Below is the sample input.

{\setlength{\abovedisplayskip}{0pt}
\begin{flalign*}
x\mathbf{e}_1 + y\mathbf{e}_2 &= x\mathbf{f}_2 + y(-\mathbf{f}_1 - \mathbf{f}_2) &\\
&= -y\mathbf{f}_1 + (x-y)\mathbf{f}_2 &\\
&= w\mathbf{f}_1 + z\mathbf{f}_2  &
\end{flalign*}}
where $w = -y$ and $z = x - y$.


Here's the corresponding output:

-
Welcome to TeX.SE. Simply adding \setlength{\belowdisplayskip}{0pt} right after \setlength{\abovedisplayskip}{0pt} seems to do it for me. But perhaps there is something else going on, so keep in mind that while code snippets are useful in explanations, it is always best to compose a fully compilable MWE that illustrates the problem including the \documentclass and the appropriate packages so that those trying to help don't have to recreate it. –  Peter Grill Mar 5 '13 at 18:50
Hey, it doesn't work in my case. Anyway, introducing the new environment as shown in the answer works for me. Thanks anyway. –  Markeur Mar 5 '13 at 19:05

You miss setting also \belowdisplayskip. However, as it's clear from the image, a spurious space will be inserted. You're better served with a new environment:

\documentclass{article}
\usepackage{amsmath}

\newenvironment{nospaceflalign*}
{\setlength{\abovedisplayskip}{0pt}\setlength{\belowdisplayskip}{0pt}%
\csname flalign*\endcsname}
{\csname endflalign*\endcsname\ignorespacesafterend}

\begin{document}
Some irrelevant text above
\begin{nospaceflalign*}
x\mathbf{e}_1 + y\mathbf{e}_2 &= x\mathbf{f}_2 + y(-\mathbf{f}_1 - \mathbf{f}_2) &\\
&= -y\mathbf{f}_1 + (x-y)\mathbf{f}_2 &\\
&= w\mathbf{f}_1 + z\mathbf{f}_2  &
\end{nospaceflalign*}
where $w = -y$ and $z = x - y$.
\end{document}


Using \csname flalign*\endcsname in this case is necessary because the environment has a * in its name and the \begin{flalign*} form can't be used for technical reasons related to how amsmath processes alignment environments.

With \ignorespacesafterend we solve the spurious space issue. If later you want to modify the rendering, it will be easier to act on the definition, rather than on the document.

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It works for me. Thanks very much for the solution. –  Markeur Mar 5 '13 at 19:05