# Too much white space after large equation in memoir class

I'm currently writing my thesis using the memoir class and I have experienced some unwanted behavior when typing large equations. LaTeX adds a ridiculous amount of vertical white space to place the equation number when the equation itself is page-wide.

An example: the following code

This is an example of the ridiculous amount of white space added:
\begin{align}
\begin{cases}
eqn_1 &= a + b + \cdots \quad \text{(just typing a page-wide equation here)} \quad \cdots + y+z\\
eqn_2 &= \text{(another equation)}\\
\vdots& \\
\vdots & \\
eqn_n &= \text{(the last equation)}
\end{cases}
\end{align}
How to fix it?


Can anyone help me with this issue? Thank you!

• why are you using align here? you have no alignment point and only one row??? – David Carlisle Sep 9 '19 at 11:00
• That much space looks like a page breaking issue. You should post a Minimal Working Example. – Teepeemm Sep 9 '19 at 15:25
• You might want to change the title as this has nothing to do with the memoir class. Change it to something more suitable to your question, such such that it is useful for others in the future. – daleif Sep 9 '19 at 15:38

Your equation is too wide, causing the number to be placed below, rather than adjacent to, the equation. You must strive to break the long (full-width) line into multiple, shorter lines.

Also, as David noted, there is no need for the outer align, as you only have one row to align. I replaced with the equation environment.

I propose doing this by way of aligned:

\documentclass[11pt]{memoir}
\usepackage{amsmath}

\begin{document}

\noindent This is an example of the ridiculous amount of white space added:
\begin{cases} eqn_1 &=\begin{aligned}[t] & a + b + \cdots \quad \text{(just typing a page-wide equation here)}\\ & \cdots + y+z\end{aligned}\\ eqn_2 &= \text{(another equation)}\\ \vdots& \\ \vdots & \\ eqn_n &= \text{(the last equation)} \end{cases}
How to fix it?

\end{document}


• Thank you Steven for the suggestion, however, this does not remove the excessive amount of vertical white space added right after the entire equation. – Ashes Sep 9 '19 at 11:11
• @Ashes Then you need to provide not just a snippet of code, but a full (but small) code example, beginning with \documentclass, which demonstrates the issue. You may edit your question to achieve this. – Steven B. Segletes Sep 9 '19 at 11:12
• @Ashes see the image posted here How to fix it? comes straight after the equation, what space are you seeing? – David Carlisle Sep 9 '19 at 11:33

I can't reproduce the huge space. However, it's possible to move up the equation number by reducing the display's width.

Also, you're misusing cases: the alignment point is for stating conditions, not for aligning the right-hand side of equations.

This is solved by nesting aligned in cases.

Next, split the overlong expression with the help of mathtools and its multlined environment.

Don't use align for single equations (and cases counts as one).

\documentclass{memoir}
\usepackage{amsmath,mathtools}

\begin{document}

This is an example of the ridiculous amount of white space added:
\begin{cases} \begin{aligned} eqn_1 &= \begin{multlined}[t] a + b + \dots \text{(just typing a page-wide equation here)}\\ +\dots + y+z \end{multlined}\\ eqn_2 &= \text{(another equation)}\\ \vdots& \\ \vdots & \\ eqn_n &= \text{(the last equation)} \end{aligned} \end{cases}
How to fix it?

\end{document}