# Handling long equations with multline

So I'm writing a report for my final year engineering project. I've got some very long equations that I'm having to handle and I'm fairly new to LaTeX.

The equation I'm trying to split is:

\begin{multline*}
\dot{S_v} = \frac{\mu_{tot}}{T} **\left[** 2\left( \left( \frac{\partial u}{\partial x}\right)^2 + \left( \frac{\partial v}{\partial y}\right)^2 + \left( \frac{\partial w}{\partial z}\right)^2 \right) + 2 \left[\frac{\partial v}{\partial x}\frac{\partial u}{\partial y} +\frac{\partial w}{\partial x}\frac{\partial u}{\partial z} +\frac{\partial w}{\partial y}\frac{\partial v}{\partial z}\right] + \left(\frac{\partial u}{\partial y}\right)^2 + \left(\frac{\partial u}{\partial z}\right)^2 + \left(\frac{\partial v}{\partial x}\right)^2 + \left(\frac{\partial v}{\partial z}\right)^2 + \left(\frac{\partial w}{\partial x}\right)^2 + \left(\frac{\partial w}{\partial y}\right)^2 **\right]**
\end{multline*}


But as soon as I add \\ to split my equation the \left[ and \right] don't opperate correctly. Any ideas?

This equation is roughly how I want it to look. I just need two large square brackets around it.

\begin{multline*}
\dot{S_v} =  \frac{\mu_{tot}}{T} 2\left( \left( \frac{\partial u}{\partial x}\right)^2 + \left( \frac{\partial v}{\partial y}\right)^2 + \left( \frac{\partial w}{\partial z}\right)^2 \right) \\ + 2 \left[\frac{\partial v}{\partial x}\frac{\partial u}{\partial y} +\frac{\partial w}{\partial x}\frac{\partial u}{\partial z} +\frac{\partial w}{\partial y}\frac{\partial v}{\partial z}\right] + \\ \left(\frac{\partial u}{\partial y}\right)^2 + \left(\frac{\partial u}{\partial z}\right)^2 + \left(\frac{\partial v}{\partial x}\right)^2 + \\ \left(\frac{\partial v}{\partial z}\right)^2 + \left(\frac{\partial w}{\partial x}\right)^2 + \left(\frac{\partial w}{\partial y}\right)^2
\end{multline*}


Thanks!

• Welcome to TeX.SX! Please help us to help you and add a minimal working example (MWE) that illustrates your problem. It will be much easier for us to reproduce your situation and find out what the issue is when we see compilable code, starting with \documentclass{...} and ending with \end{document}. – user31729 Feb 15 '15 at 13:01

Routine rant

You need \right. before \\ and \left. at fore front of second line like

\left[......\right. \\
\left. .......\right]


since \left[ and \right] can't be broken across the line without balancing.

Routine recommended solution

You need \Biggl[ and \Biggr] from amsmath

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{multline*}
\dot{S_v} = \frac{\mu_{tot}}{T} \Biggl[ 2\left( \left( \frac{\partial u}{\partial x}\right)^2 + \left( \frac{\partial v}{\partial y}\right)^2 + \left( \frac{\partial w}{\partial z}\right)^2 \right) + 2 \left[\frac{\partial v}{\partial x}\frac{\partial u}{\partial y} +\frac{\partial w}{\partial x}\frac{\partial u}{\partial z} +\frac{\partial w}{\partial y}\frac{\partial v}{\partial z}\right] \\
+ \left(\frac{\partial u}{\partial y}\right)^2 + \left(\frac{\partial u}{\partial z}\right)^2 + \left(\frac{\partial v}{\partial x}\right)^2 + \left(\frac{\partial v}{\partial z}\right)^2 + \left(\frac{\partial w}{\partial x}\right)^2 + \left(\frac{\partial w}{\partial y}\right)^2 \Biggr]
\end{multline*}
\end{document}


• Some (minor) observations: The first outer \left(...\right) group (immediately after \Biggl[ produces fences that are a bit too large, typographically speaking. To make them the same size as the subsequent square brackets, and to highlight the math kinship (both "groups" are prefixed with a multiplicative factor of 2), I'd use \biggl[... \,\biggr]. (The thinspace, \,, helps avoid a clash with the preceding superscript 2.) – Mico Feb 15 '15 at 16:08