empheq 中的新行

Question

我有一个大等式，想用 empheq 来拆分：

\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}

我曾尝试用\\和来破解我的方程式，\newline但没有用……？

Answer 1

我会使用align*环境和单个换行符指令。我不会自动调整括号的大小，而是使用\bar而不是\overline。为了提高可读性，如果您使用 Computer Modern 作为文档字体，请考虑在或后跟右括号时插入\,(thinspace) 。\vec{r}\vec{\xi}

\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}

Answer 2

不是使用empheq，而是使用更标准的工具：

\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}

经过一些改进，基本上\,是在向量后面紧跟着一个括号时添加：

\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}

Answer 3

我不知道这个建议的替代方案是否适合使用堆栈，而不是??请注意，我保留了您最初的empheq数学运算。\textstyle

\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}

如果想要方程\displaystyle，那么

1. 添加\TABstackMathstyle{\displaystyle}到序言中；

2. 改为;\ensurestackMath并且\ensureTABstackMath

3. 改成。\Shortunderstack​\tabbedShortunderstack

结果如下：

Answer 4

一种变体，始终使用rcases，使用\widebar从借用的命令mathabx和从中借用的 bvector 箭头，在我看来，esvect它比基本的看起来更好看：vec

\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}