# new line in empheq

I have a big equation that I want to split with empheq :

\begin{empheq}[right={\empheqrbrace =  - \oint_S \frac{\overline{\overline{G}}(\vec{r}-\vec{\xi})}{8\pi \mu}\left(\overline{\overline{\sigma}}(\vec{r})\vec{n}\right)dS  + \oint_S \vec{v}(\vec{r})\left(\frac{\overline{\overline{\overline{\Sigma}}}(\vec{r}-\vec{\xi})}{8\pi \mu}\vec{n}\right)dS - \oint_S \frac{ \overline{\overline{G}}(\vec{r}-\vec{\xi})}{8\pi \mu}\left(\overline{\overline{\sigma}}(\vec{r})\vec{n}\right)dS  + \oint_S \vec{v}(\vec{r})\left(\frac{\overline{\overline{\overline{\Sigma}}}(\vec{r}-\vec{\xi})}{8\pi \mu}\vec{n}\right)dS }]{align*}
\text{si $V \in V_p$,}& 0  \\
\text{si $V \notin V_p$,}& \vec{v}_p
\end{empheq}


I have tried to break my equation with \\ and \newline but it doesn't work ... ?

• ok, it works. Mico response is the simpliest for me. thank you everyone – Kafka Jan 6 '17 at 16:37
• Just to explain why this does not work: what you essentially have here is similar to \begin{equation*} \begin{aligned} TEXT\end{aligned} \} = RIGHT \end{equation*}, so as the others have pointed out, you probably want to do this differently. – daleif Jan 6 '17 at 16:38

I would use an align* environment and a single line break directive. I wouldn't autosize the parentheses, and I'd use \bar instead of \overline. For better legibility, if you're using Computer Modern as the document font, consider inserting \, (thinspace) if \vec{r} or \vec{\xi} is followed by a closing parenthesis.

\documentclass[12pt]{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
\left.\begin{array}{ll}
\text{si $V \in V_p$,    } & 0  \1ex] \text{si V \notin V_p, } & \vec{v}_p \end{array}\right\} &= - \oint_S \frac{\bar{\bar{G}}(\vec{r}-\vec{\xi}\,)}{8\pi \mu}\bigl(\bar{\bar{\sigma}}(\vec{r}\,)\vec{n}\bigr)dS + \oint_S \vec{v}(\vec{r}\,)\biggl(\frac{\bar{\bar{\bar{\Sigma}}}(\vec{r}-\vec{\xi}\,)}{8\pi \mu}\vec{n}\biggr)dS \\ &\quad - \oint_S \frac{ \bar{\bar{G}}(\vec{r}-\vec{\xi}\,)}{8\pi \mu}\bigl(\bar{\bar{\sigma}}(\vec{r}\,)\vec{n}\bigr)dS + \oint_S \vec{v}(\vec{r}\,)\biggl(\frac{\bar{\bar{\bar{\Sigma}}}(\vec{r}-\vec{\xi}\,)}{8\pi \mu}\vec{n}\biggr)dS \end{align*} \end{document}  Not with empheq, but with more standard tools: \documentclass{article} \usepackage{amsmath} \usepackage{mathtools} \newcommand{\ov}[1]{\overline{#1}} \newcommand{\oov}[1]{\overline{\overline{#1}}} \newcommand{\ooov}[1]{\overline{\overline{\overline{#1}}}} \begin{document} \begin{equation*} \begin{rcases} \text{si V \in V_p,} & 0 \\ \text{si V \notin V_p,} & \vec{v}_p \end{rcases} =\begin{aligned}[t] & - \oint_S \frac{\oov{G}(\vec{r} - \vec{\xi})}{8\pi \mu} (\oov{\sigma}(\vec{r})\vec{n})\,dS + \oint_S \vec{v}(\vec{r})\Biggl(\frac{\ooov{\Sigma}(\vec{r} - \vec{\xi})}{8\pi \mu} \vec{n}\Biggr)\,dS \\ & - \oint_S \frac{ \oov{G}(\vec{r} - \vec{\xi})}{8\pi \mu} (\oov{\sigma}(\vec{r})\vec{n})\,dS + \oint_S \vec{v}(\vec{r})\Biggl(\frac{\ooov{\Sigma}(\vec{r} -\vec{\xi})}{8\pi \mu} \vec{n}\Biggr)\,dS \end{aligned} \end{equation*} \end{document}  With some refinements, basically adding \, when a vector is immediately followed by a parenthesis: \documentclass{article} \usepackage{amsmath} \usepackage{mathtools} \newcommand{\ov}[1]{\overline{#1}} \newcommand{\oov}[1]{\overline{\overline{#1}}} \newcommand{\ooov}[1]{\overline{\overline{\overline{#1}}}} \begin{document} \begin{equation*} \begin{rcases} \text{si V \in V_p,} & 0 \\ \text{si V \notin V_p,} & \vec{v}_p \end{rcases} =\begin{aligned}[t] & - \oint_S \frac{\oov{G}(\vec{r} - \vec{\xi}\,)}{8\pi \mu} (\oov{\sigma}(\vec{r}\,)\vec{n}\,)\,dS + \oint_S \vec{v}(\vec{r})\Biggl(\,\frac{\ooov{\Sigma}(\vec{r} - \vec{\xi}\,)}{8\pi \mu} \vec{n}\Biggr)\,dS \\ & - \oint_S \frac{ \oov{G}(\vec{r} - \vec{\xi}\,)}{8\pi \mu} (\oov{\sigma}(\vec{r}\,)\vec{n}\,)\,dS + \oint_S \vec{v}(\vec{r}\,)\Biggl(\,\frac{\ooov{\Sigma}(\vec{r} -\vec{\xi}\,)}{8\pi \mu} \vec{n}\Biggr)\,dS \end{aligned} \end{equation*} \end{document}  I don't know if this proposed alternative might suit, using stacks, rather than empheq?? Note I left the math in \textstyle as you originally had it. \documentclass{scrartcl} \usepackage{empheq,tabstackengine} \begin{document} Was: \begin{empheq}[right={\empheqrbrace = - \oint_S \frac{\overline{\overline{G}}(\vec{r}-\vec{\xi})}{8\pi \mu}\left(\overline{\overline{\sigma}}(\vec{r})\vec{n}\right)dS + \oint_S \vec{v}(\vec{r})\left(\frac{\overline{\overline{\overline{\Sigma}}}(\vec{r}-\vec{\xi})}{8\pi \mu}\vec{n}\right)dS - \oint_S \frac{ \overline{\overline{G}}(\vec{r}-\vec{\xi})}{8\pi \mu}\left(\overline{\overline{\sigma}}(\vec{r})\vec{n}\right)dS + \oint_S \vec{v}(\vec{r})\left(\frac{\overline{\overline{\overline{\Sigma}}}(\vec{r}-\vec{\xi})}{8\pi \mu}\vec{n}\right)dS }]{align*} \text{si V \in V_p,}& 0 \\ \text{si V \notin V_p,}& \vec{v}_p \end{empheq} Proposed: \[ \left. \begin{aligned} \text{si V \in V_p,}& 0 \\ \text{si V \notin V_p,}& \vec{v}_p \end{aligned} \right\}= \ensurestackMath{\Shortunderstack {- \oint_S \frac{\overline{\overline{G}}(\vec{r}-\vec{\xi})}{8\pi \mu}\left(\overline{\overline{\sigma}}(\vec{r})\vec{n}\right)dS + \oint_S \vec{v}(\vec{r})\left(\frac{\overline{\overline{\overline{\Sigma}}}(\vec{r}-\vec{\xi})}{8\pi \mu}\vec{n}\right)dS \\ -\oint_S \frac{ \overline{\overline{G}}(\vec{r}-\vec{\xi})}{8\pi \mu}\left(\overline{\overline{\sigma}}(\vec{r})\vec{n}\right)dS + \oint_S \vec{v}(\vec{r})\left(\frac{\overline{\overline{\overline{\Sigma}}}(\vec{r}-\vec{\xi})}{8\pi \mu}\vec{n}\right)dS }}
\end{document}


If one wanted the equation in \displaystyle, then

1. add \TABstackMathstyle{\displaystyle} to the preamble;

2. change \ensurestackMath to \ensureTABstackMath; and

3. change \Shortunderstack to \tabbedShortunderstack.

Here is the result:

A variant, always with rcases, using the \widebar command, borrowed from mathabx, and the bvector arrows from esvect, which look nicer than the basic vec, in my opinion:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{empheq}
\usepackage[f]{esvect} %
\DeclareFontFamily{U}{mathx}{\hyphenchar\font45}
\DeclareFontShape{U}{mathx}{m}{n}{
<5><6><7><8><9><10>
<10.95><12><14.4><17.28><20.74><24.88>
mathx10
}{}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}
\DeclareFontSubstitution{U}{mathx}{m}{n}
\DeclareMathSymbol{\bigboxvoid}{\mathop}{mathx}{"DC}
\DeclareMathAccent{\widebar}{0}{mathx}{"73}

\begin{document}

\begin{align*}
\begin{rcases} \text{si } V ∈ V_p , & 0 \\
\text{si }V ∉ V_p, & \vv{v}_p
\end{rcases}
= & - ∮_S \frac{\widebar{\widebar{G}}(\vv{r}-\vv{ξ})}{8πμ}\left(\widebar{\widebar{σ}}(\vv{r})\vv{n}\right)dS + ∮_S \vv{v}(\vv{r})\left(\frac{\widebar{\widebar{\widebar{Σ}}}(\vv{r}-\vv{ξ})}{8πμ}\vv{n}\right)dS \\
& - ∮_S \frac{ \widebar{\widebar{G}}(\vv{r}-\vv{ξ})}{8πμ}\left(\widebar{\widebar{σ}}(\vv{r})\vv{n}\right)dS + ∮_S \vv{v}(\vv{r})\left(\frac{\widebar{\widebar{\widebar{Σ}}}(\vv{r}-\vv{ξ})}{8πμ}\vv{n}\right)dS
\end{align*}

\end{document}