[Tex/LaTex] eqnarray and cases

math-mode

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?

Best Answer

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:

enter image description here

\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}
Related Question