3

How do I put multiple empheq environments side-by-side? Like this:

\documentclass{article}

\usepackage{empheq}

\begin{document}

\begin{empheq}[left=\empheqlbrace]{align*}
&\frac{1}{n} > \frac{1}{n^2} \\
&{a'}^2 - \frac{2a'}{n} + \frac{1}{n^2} > 2
\end{empheq}

\begin{empheq}[left=\empheqlbrace]{align*}
&\frac{1}{n} > \frac{1}{n^2} \\
&\frac{1 - 2a'}{n} > 2 - {a'}^2
\end{empheq}

\end{document}

but side-by-side and with a mandatory \implies between the environments.

  • I don't think you need align* nor empheq, as cases (requires amsmath) is sufficient. – egreg May 30 '14 at 22:59
  • @egreg, is it possible to insert braces on the left of equation systems using cases? – Egor Tensin May 30 '14 at 23:04
  • Yes, that's the purpose of cases. – egreg May 30 '14 at 23:04
2

I'd go with dcases from mathtools:

\documentclass{article}

\usepackage{mathtools}

\begin{document}
\[
\begin{dcases}
\frac{1}{n} > \frac{1}{n^2} \\[1ex]
a'^2 - \frac{2a'}{n} + \frac{1}{n^2} > 2
\end{dcases}
\quad\implies\quad
\begin{dcases}
\frac{1}{n} > \frac{1}{n^2} \\[1ex]
\frac{1 - 2a'}{n} > 2 - a'^2
\end{dcases}
\]
\end{document}

enter image description here

  • thanks! Any chance the brace can be lengthy enough to cover 1s? I just don't particularly like the fact that they're above the brace. – Egor Tensin May 30 '14 at 23:12
  • @EgorTensin that's a feature of dcases, I guess, but I don't dislike it. Try with cases, but changing every \frac into \dfrac and [1ex] into [2ex]. – egreg May 30 '14 at 23:23
  • Ok, I just went with the regular cases environment, but with the fractions displayed in a lesser size. Could you please guide me on weather it's good style or not? – Egor Tensin May 30 '14 at 23:40
  • @EgorTensin As I said, use \dfrac – egreg May 30 '14 at 23:44
  • Yeah, it turned out to be ok with the fractions (as far as I understand) being typeset in "display style". The issue with the spacing though. There are no spacing issues with the regular fracs, I just thought it might be an example of bad style to typeset this way. Or isn't it? It looks more or less OK to me. – Egor Tensin May 30 '14 at 23:48
1

You can roll your own in a number of ways. Here's one using an array:

enter image description here

\documentclass{article}

\usepackage{amsmath}

\begin{document}

\[
  \renewcommand{\arraystretch}{2.1}% http://tex.stackexchange.com/q/31672/5764
  \left\{\begin{array}{l@{}}
    \dfrac{1}{n} > \dfrac{1}{n^2} \\
    {a'}^2 - \dfrac{2a'}{n} + \dfrac{1}{n^2} > 2
  \end{array}\right. \quad \implies \quad
  \left\{\begin{array}{l@{}}
    \dfrac{1}{n} > \dfrac{1}{n^2} \\
    \dfrac{1 - 2a'}{n} > 2 - {a'}^2
  \end{array}\right.
\]

\end{document}
  • thanks, not the first time you save my day! I'll try to stick to the ready-made solution using mathtools though. – Egor Tensin May 30 '14 at 23:07

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