109

How do I typeset something like, X = 0 if a=1, 1 otherwise, using those huge left braces and specifying each condition in a line?

155

The cases environment from amsmath does the trick.

\documentclass{article}
\usepackage{amsmath}

\begin{document}
  \begin{equation}
    X=
    \begin{cases}
      0, & \text{if}\ a=1 \\
      1, & \text{otherwise}
    \end{cases}
  \end{equation}
\end{document}

Result

| improve this answer | |
25

Another method, which is especially helpful if one needs to have more control over the items alignment, is the array construct.

\documentclass{article}
\usepackage{amsmath}    
\begin{document}

\begin{equation}
  X=\left\{
  \begin{array}{@{}ll@{}}
    0, & \text{if}\ a=1 \\
    1, & \text{otherwise}
  \end{array}\right.
\end{equation} 

\end{document}

enter image description here

Instead of ll, one may choose cc, rr, rl, etc. Besides, all the array capabilities can be applied here (\arraycolsep, \arraystretch, \extrarowheight by loading the array package, etc).

One more alternative could be using the aligned environment and adding the pseudo-parenthesis ., which can be used to terminate an opening parenthesis {.

\documentclass{article}
\usepackage{amsmath}    
\begin{document}

\begin{equation}
  X = \left \{
  \begin{aligned}
    &0, && \text{if}\ a=1 \\
    &1, && \text{otherwise}
  \end{aligned} \right.
\end{equation} 

\end{document}

enter image description here

| improve this answer | |
21
x = \begin{cases}
  0, & \text{if } a = 1, \\
  1, & \text{otherwise}.
\end{cases}

amsmath is needed for \text.

| improve this answer | |
4

Iverson bracket can also be used: $x=[a \neq 1]$.

| improve this answer | |
  • Knuth is a fan of Iverson notation, using it heavily in Concrete Mathematics among other publications. BTW, here to match the original question, I think you mean $x = [a \neq 1]$ :-) – ShreevatsaR Jan 16 '17 at 17:30

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