2

Here's my problem : I'd like to a write many equivalent systems of equations. Therefore, I'd like the first to be at the left, then an arrow (\Leftrightarrow, for example, since they're equivalent :)), a second one on the right, and then, the others vertically aligned with the second. Basically, I want to do the same thing that can be done with the align environment, but with systems. Nevertheless, I didn't figure it out.

Here's what I tried :

\documentclass[11pt]{article}
\usepackage{envmath}
\begin{document} 
\[
\begin{System} 
  x + y = 3 \\ 
  x - y = 1
\end{System} \Leftrightarrow 
\begin{System}
 x=2\\ 
 y=1
\end{System}
\]
\end{document}

Would you have any solution ?

  • Would you have examples of these systems to start with? – percusse Mar 16 '14 at 16:48
  • @Araen, you can edit your posts Although the "edit" link is a little hard to see. I've moved your comment into your post. – Thruston Mar 16 '14 at 17:00
  • amsmath is better than envmath. – egreg Mar 17 '14 at 8:59
2

You could use aligned and \iff which produces the correct math spacing:

enter image description here

Code:

\documentclass[11pt]{article}
\usepackage{amsmath}

\begin{document} 
\[
    \left\{\begin{aligned} 
      x + y &= 3 \\ 
      x - y &= 1
    \end{aligned}\right. \iff 
    \left\{\begin{aligned}
     x &= 2\\ 
     y &= 1
    \end{aligned}\right.
\]
\end{document}
1

Put everything in a tabular environment:

\documentclass[11pt]{article}

\begin{document}

\begin{tabular}{lll}
    $\left\{\begin{tabular}{l}x+y=3 \\ x-y=1 \\ \end{tabular}\right.$ & $\Leftrightarrow$ & $\left\{\begin{tabular}{l}x=2 \\ y=1 \\ \end{tabular}\right.$ \\
    & & \\
    & $\Leftrightarrow$ & $\left\{\begin{tabular}{l}x=2 \\ y=1 \\ \end{tabular}\right.$ \\
\end{tabular}

\end{document}

enter image description here

  • Are you sure about tabular? Shouldn't it be array? – egreg Mar 17 '14 at 8:53
0

Without any package:

\documentclass{article}
\begin{document} 
\[
\left\{\!\!\begin{array}{c}
x+y=3\\
x-y=1
\end{array}\right. 
\!\!\Leftrightarrow
\left\{\!\!
\begin{array}{c}
x=2\\
y=1 
\end{array}
\right. 
\]
\end{document}

The negative spaces \!\! are to obtain a spacing similar to Peter's answer, but may be is OK for you with some more spacing around the brackets. This is the difference:

MWE

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