Large braces for specifying values of variables by condition

Question

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?

Answer 1

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}

Answer 2

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}

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}

Answer 3

x = \begin{cases}
  0, & \text{if } a = 1, \\
  1, & \text{otherwise}.
\end{cases}

amsmath is needed for \text.

Answer 4

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

Answer 5

Here is a way to manually control the size of brace, if cases or \left\{ doesn't provide suitable brace size you want.

\begin{math}
\biggl\{
    \begin{array}{l}
        statement1\\
        statement2
    \end{array}
\end{math}

You can choose among \bigl\{ \Bigl\{ \biggl\{ \Biggl\{ to adjust brace size from the smallest to the largest.

From left to right: cases \left\{ biggl\{ Bigl\{