# eqnarray and cases

I have quite a strange tex style from the conference. Everything is fine, but the following code does not work here:

\begin{eqnarray}
a = \begin{cases} 1 \\
2
\end{cases}
\end{eqnarray}


does not seem to work here in conjunction with eqnarray, which is also required. Is it possible to mimic the behaviour of cases in this case?

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I threw that into the tex file contained in your link and it seemed to produce the correct output after adding \usepackage{amsmath} to the preamble. Have you loaded amsmath? – Scott H. Jul 15 '12 at 18:11
Yep, it seems so. Thank you! – Ivan Oseledets Jul 15 '12 at 23:43

eqnarray is not required in order for cases to work. Moreover, it's deprecated in terms of its support/usage and should therefore not be used. Rather use align (see \eqnarray vs \align. You're most likely after:

\documentclass{article}
\usepackage{amsmath}% http://ctan.org/pkg/amsmath
\begin{document}
\begin{align*}
a = \begin{cases}
x & \text{if $y=1$} \\
z & \text{if $b=2$}
\end{cases}
\end{align*}
\end{document}


amsmath provides cases as well as \text and align, although align is technically not needed for such an elementary equation. Using an equation environment (or unnumbered $ ... $) would suffice.

You could also obtain the above output manually using

\documentclass{article}
\begin{document}
$a = \left\{\begin{array}{@{}l@{\quad}l} x & \mbox{if y=1} \\[\jot] z & \mbox{if b=2} \end{array}\right.$
\end{document}

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Why not use a simple $...$? align is not needed here! – Hendrik Vogt Jul 16 '12 at 15:59
@HendrikVogt: That's correct. In the spirit of the original question, I kept the align. I'll update the answer accordingly. – Werner Jul 16 '12 at 16:02
@Werner The original question uses eqnarray where it shouldn't to begin with, because there's no alignment. The "correct" answer would use equation. – egreg Jul 16 '12 at 16:37