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I'm trying to write a system of 3 equations, subnumerated, left-aligned with a big left brace, compiled with pdflatex.

So far I tried the subequations with empheq environment:

\begin{subequations}
\begin{empheq}[left={\empheqlbrace\,}]{align}
& \delta \underline{v}^{T} \int_{\Omega} \left( \D : \underline{\nabla}^{s} \underline{v} \right) \underline{\nabla}^{s} \mathrm{d} \Omega + \int_{\Omega} \left( \underline{a} \, \underline{a}^{T} \right) \underline{\nabla} T \mathrm{d} \Omega + \int_{\Omega} \underline{\nabla} P \mathrm{d} \Omega - \int_{\Omega} \underline{f}_{b} \mathrm{d} \Omega - \int_{\Gamma} \underline{f}_{s} \mathrm{d} \Gamma \\
& \delta P \int_{\Omega} \underline{\nabla} \cdot \underline{v} \mathrm{d} \Omega \\
& \delta T \int_{\Omega} \underline{\nabla}^{s} \underline{v} : \left( \underline{a} \, \underline{a}^{T} \right) \mathrm{d} \Omega
\end{empheq}
\end{subequations}

resulting in a first equation too long (I can't reduce the size of the font). I then tried adding a split tag:

\begin{subequations}
\begin{empheq}[left={\empheqlbrace\,}]{align}
& \begin{split} \delta \underline{v}^{T} \int_{\Omega} \left( \D : \underline{\nabla}^{s} \underline{v} \right) \underline{\nabla}^{s} \mathrm{d} \Omega + \int_{\Omega} \left( \underline{a} \, \underline{a}^{T} \right) \underline{\nabla} T \mathrm{d} \Omega + \int_{\Omega} \underline{\nabla} P \mathrm{d} \Omega \\ - \int_{\Omega} \underline{f}_{b} \mathrm{d} \Omega - \int_{\Gamma} \underline{f}_{s} \mathrm{d} \Gamma \end{split} \\
& \delta P \int_{\Omega} \underline{\nabla} \cdot \underline{v} \mathrm{d} \Omega \\
& \delta T \int_{\Omega} \underline{\nabla}^{s} \underline{v} : \left( \underline{a} \, \underline{a}^{T} \right) \mathrm{d} \Omega
\end{empheq}
\end{subequations}

resulting in a first equation not properly aligned.

Same alignment problem appears with the align environment:

\begin{align}
& \begin{split} \delta \underline{v}^{T} \int_{\Omega} \left( \D : \underline{\nabla}^{s} \underline{v} \right) \underline{\nabla}^{s} \mathrm{d} \Omega + \int_{\Omega} \left( \underline{a} \, \underline{a}^{T} \right) \underline{\nabla} T \mathrm{d} \Omega + \int_{\Omega} \underline{\nabla} P \mathrm{d} \Omega \\ - \int_{\Omega} \underline{f}_{b} \mathrm{d} \Omega - \int_{\Gamma} \underline{f}_{s} \mathrm{d} \Gamma \end{split} \\
& \delta P \int_{\Omega} \underline{\nabla} \cdot \underline{v} \mathrm{d} \Omega \\
& \delta T \int_{\Omega} \underline{\nabla}^{s} \underline{v} : \left( \underline{a} \, \underline{a}^{T} \right) \mathrm{d} \Omega
\end{align}

so it propbably has something to do with the split tag, but multline is apparently forbidden in subequations or align environment.

How can I format these equations the way I want?

  • Welcome to TeX.SE! Please, expand your code sniped to complete small document. Now we can only guess what is \D ... – Zarko Jun 6 '17 at 17:43
  • Sorry, forgot about that. \D is the letter D with four \underline. I think it's the only one I forgot. – G. Sorba Jun 6 '17 at 17:53
  • OK thanks for the information. Next time I'll be more careful. – G. Sorba Jun 6 '17 at 18:44
2

making a wild guess that \D is meant to be \Delta, here is one approach.

\documentclass{article}
\usepackage{mathtools}
\usepackage{cases}
\newcommand{\D}{\Delta}
\begin{document}

\begin{subnumcases}{}
 \begin{multlined} \delta \underline{v}^{T} \int_{\Omega} \left( \D : \underline{\nabla}^{s} \underline{v} \right) \underline{\nabla}^{s} \mathrm{d} \Omega + \int_{\Omega} \left( \underline{a} \, \underline{a}^{T} \right) \underline{\nabla} T \mathrm{d} \Omega + \int_{\Omega} \underline{\nabla} P \mathrm{d} \Omega \\ - \int_{\Omega} \underline{f}_{b} \mathrm{d} \Omega - \int_{\Gamma} \underline{f}_{s} \mathrm{d} \Gamma \end{multlined} \\
 \delta P \int_{\Omega} \underline{\nabla} \cdot \underline{v} \mathrm{d} \Omega \\
 \delta T \int_{\Omega} \underline{\nabla}^{s} \underline{v} : \left( \underline{a} \, \underline{a}^{T} \right) \mathrm{d} \Omega
\end{subnumcases}

\end{document}

enter image description here

| improve this answer | |
  • This is exactly what I was looking for, thanks! – G. Sorba Jun 6 '17 at 18:08
2

Use aligned instead of split. I also simplified the code and defined a \dd command for the differential symbol with a better spacing. The equation number of the first, multilined equation is vertically centred by default, but it can be aligned with the first line adding the [t] option.

\documentclass{article}
\usepackage{empheq}
\newcommand\D{{D}}
\newcommand*{\dd}{\mathop{\kern0pt\mathrm{d}}\mkern-2.5mu{}}%

    \begin{document}

\begin{subequations}
\begin{empheq}[left={\empheqlbrace\,}]{align}
&\begin{aligned}\delta \underline{v}^{T}\int_{\Omega}( \D : \underline{\nabla}^{s} \underline{v}) \underline{\nabla}^{s} \dd \Omega+ \int_{\Omega} \bigl( \underline{a} \, \underline{a}^{T} \bigr) \underline{\nabla} T \dd \Omega+ \int_{\Omega} \underline{\nabla} P \dd \Omega \\ - \int_{\Omega} \underline{f}_{b} \dd \Omega - \int_{\Gamma} \underline{f}_{s} \dd \Gamma\end{aligned} \\
& \delta P \int_{\Omega} \underline{\nabla} \cdot \underline{v} \dd\Omega \\
& \delta T \int_{\Omega} \underline{\nabla}^{s} \underline{v} : \bigl( \underline{a} \, \underline{a}^{T} \bigr) \dd \Omega
\end{empheq}
\end{subequations}

\end{document} 

enter image description here

Edit: Adding this code to your preamble:

\DeclareFontFamily{U}{mathx}{\hyphenchar\font45}
\DeclareFontShape{U}{mathx}{m}{n}{
<-6> mathx5 <6-7> mathx6 <7-8> mathx7
<8-9> mathx8 <9-10> mathx9
<10-12> mathx10 <12-> mathx12
}{}
\DeclareSymbolFont{mathx}{U}{mathx}{m}{n}
\DeclareFontSubstitution{U}{mathx}{m}{n}
\DeclareMathSymbol{\bigboxvoid}{\mathop}{mathx}{"DC}
\DeclareMathAccent{\widebar}{0}{mathx}{"73}
\newcommand\uwidebar[1]{\underaccent{\widebar}{#1}}
\newcommand\D{\uwidebar{\uwidebar{\uwidebar{\uwidebar{D}}}}}
\newcommand\unabla{\uwidebar{\nabla\mkern2mu}\mkern-2mu}

you can use the widebar command from mathbx as an \underaccent, which looks nicer in my opinion. The new mainbody code will be:

\begin{subequations}
\begin{empheq}[left={\empheqlbrace\,}]{align}
&\begin{aligned}[t]\delta \uwidebar{v}^{T}\int_{\Omega}( \D : \unabla^{s} \uwidebar{v}) \unabla^{s} \dd \Omega+ \int_{\Omega} \bigl( \uwidebar{a} \, \uwidebar{a}^{T} \bigr) \unabla T \dd \Omega+ \int_{\Omega} \unabla P \dd \Omega \\%
 - \int_{\Omega} \uwidebar{f}_{b} \dd \Omega - \int_{\Gamma} \uwidebar{f}_{s} \dd \Gamma\end{aligned} \\
& \delta P \int_{\Omega} \unabla \cdot \uwidebar{v} \dd\Omega \\
& \delta T \int_{\Omega} \unabla^{s} \uwidebar{v} : \bigl( \uwidebar{a} \, \uwidebar{a}^{T} \bigr) \dd \Omega
\end{empheq}
\end{subequations}

enter image description here

| improve this answer | |
0

Like this?

enter image description here

\documentclass{article}
\usepackage{empheq}
\begin{document}
with \verb+multlined+:
\begin{subequations}
\begin{empheq}[left={\empheqlbrace\,}]{align}
& \begin{multlined}[0.75\linewidth]
    \delta \underline{v}^{T} 
    \int_{\Omega} \left( D : \underline{\nabla}^{s} \underline{v} \right) \underline{\nabla}^{s} \mathrm{d} \Omega    \\ 
    + \int_{\Omega} \left( \underline{a} \, \underline{a}^{T} \right) \underline{\nabla} T \mathrm{d} \Omega
    + \int_{\Omega} \underline{\nabla} P \mathrm{d} \Omega 
    - \int_{\Omega} \underline{f}_{b} \mathrm{d} \Omega - \int_{\Gamma} \underline{f}_{s} \mathrm{d} \Gamma
    \end{multlined} \\
& \delta P \int_{\Omega} \underline{\nabla} \cdot \underline{v} \mathrm{d} \Omega \\
& \delta T \int_{\Omega} \underline{\nabla}^{s} \underline{v} : \left( \underline{a} \, \underline{a}^{T} \right) \mathrm{d} \Omega
\end{empheq}
\end{subequations}

with \verb+split+:
\begin{subequations}
\begin{empheq}[left={\empheqlbrace\,}]{align}
\begin{split}
&
    \delta \underline{v}^{T}
    \int_{\Omega} \left( D??? : \underline{\nabla}^{s} \underline{v} \right) \underline{\nabla}^{s} \mathrm{d} \Omega    \\
& + \int_{\Omega} \left( \underline{a} \, \underline{a}^{T} \right) \underline{\nabla} T \mathrm{d} \Omega
    + \int_{\Omega} \underline{\nabla} P \mathrm{d} \Omega
    - \int_{\Omega} \underline{f}_{b} \mathrm{d} \Omega - \int_{\Gamma} \underline{f}_{s} \mathrm{d} \Gamma
    \end{split} \\
& \delta P \int_{\Omega} \underline{\nabla} \cdot \underline{v} \mathrm{d} \Omega \\
& \delta T \int_{\Omega} \underline{\nabla}^{s} \underline{v} : \left( \underline{a} \, \underline{a}^{T} \right) \mathrm{d} \Omega
\end{empheq}
\end{subequations}

\end{document}
| improve this answer | |
  • That is also what I was looking for, but I prefer the layout of the previous answer. – G. Sorba Jun 6 '17 at 18:09

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