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How do I suppress the whitespace above the equation block at the page top ? It is added to the top margin, and I don't want that to happen. I know that \abovedisplayshortskip controls this for the whole document, but how can I change this for this particular equation block and NOT for any others ? Negative vspace doesn't work.

\documentclass[pdftex,12pt,a4paper,english,dutch,leqno]{article}
\usepackage[top=1cm,right=1cm,bottom=1cm,left=1.5cm,noheadfoot]{geometry}        
\usepackage{babel}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{empheq}

\begin{document}

\abovedisplayskip=6pt
\abovedisplayshortskip=3pt % This should NOT be changed
\belowdisplayskip=6pt
\belowdisplayshortskip=3pt

\begin{equation*}
\left.\begin{array}{r}
a_{31}'=a_{11}\cdot a_{31}-a_{31}\cdot a_{11}=0\\
a_{32}'=a_{11}\cdot a_{32}-a_{31}\cdot a_{12}\\
a_{33}'=a_{11}\cdot a_{33}-a_{31}\cdot a_{13}\\
a_{34}'=a_{11}\cdot a_{34}-a_{31}\cdot a_{14}\\
b_{3}'=a_{11}\cdot b_{3}-a_{31}\cdot b_{1}
\end{array}\!\!\right\}
\Longrightarrow\;
\begin{matrix*}[l]
\text{Pseudo-code :}\\
a_{11}\cdot b_{3}-a_{31}\cdot b_{1}\mapsto b_{3}\text{.}\\
\forall\;i\in\{4,3,2,1\} : a_{11}\cdot a_{3i}-a_{31}\cdot a_{1i}\mapsto a_{3i}\text{.} \end{matrix*}
\end{equation*}

\end{document}
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If the problem is that you need to move the display to the next page, add \pagebreak at the end of the text that precedes the display. The space will automatically disappear. –  egreg Nov 6 '12 at 15:49
1  
It is strongly discouraged to start a page with displayed formulas. –  Hendrik Vogt Nov 6 '12 at 16:38
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1 Answer 1

up vote 12 down vote accepted

It is not a skip that you have above the equation but a one line paragraph consisting of an indentation box and parfillskip glue. TeX display math environments do not generally react well to starting a paragraph they are designed to work mid-paragraph. If you need to do this you need to suppress the paragraph start with

\noindent
\begin{equation*}

and you will see the equation move up the page.

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