# Large braces for specifying values of variables by condition

How do I produce a conditional expression with large brackets?

For example:

X = 0 if a=1, 1 otherwise, with a large left bracket and specifying each condition in a line?

The cases environment from amsmath does the trick.

\documentclass{article}
\usepackage{amsmath}

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


• Should there be space in between a and = ; = and 1? Feb 11 at 11:21

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}

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

\end{document}


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}

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

\end{document}


• should we put . after otherwise? Feb 11 at 11:27
• In most cases, yes we should, based on the context. Feb 11 at 18:07
x = \begin{cases}
0, & \text{if } a = 1, \\
1, & \text{otherwise}.
\end{cases}


amsmath is needed for \text.

• the & characters makes the {cases} environment break for me in equations written in \begin{align*} environments using amsmath - so I put spacing in with \qquad and similar
– tom
Nov 8, 2021 at 2:09

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

• 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 $x = [a \neq 1]$ :-) Jan 16, 2017 at 17:30