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I want to produce big parenthesis like this: Left brace including several lines in eqnarray How do I do this with align instead of array? I do not want to use eqnarray though. Thanks.

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Ka Wa Yip
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    Why align? Is it because you want the components of the cases environment numbered? For that you can use numcases. Could please describe exactly what you want? – Werner May 14 '15 at 04:08
  • spacing between rows are tighter if i use array – Ka Wa Yip May 14 '15 at 05:22
  • If you want the rows to be spaced tightly, definitely do not use an align environment, since it'll typeset the material in display math mode. – Mico May 14 '15 at 06:23
  • Yes, the appearances are different. I want the rows to be spaced widely, so I hope to use align environment. Also, there are multiple advantages to use align over array (described in multiple posts in stack-exchange here). – Ka Wa Yip May 14 '15 at 21:40

1 Answers1

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You can use empheq

\documentclass{article}
\usepackage{empheq}
\begin{document}
\begin{empheq}[left={\alpha(x)= \empheqlbrace}]{align}
               &  x\\
               & \frac{1}{1+e^{-kx}}\\
               & \frac{e^x-e^{-x}}{e^x+e^{-x}}
\end{empheq}
\end{document}

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