205

I want to write a conditional expression such as the following.

enter image description here

What is the best way to express such conditional expressions in Latex?

1
  • 4
    use cases or dcases. Mar 7 '12 at 20:05
260

I think this is a job for cases from the amsmath package

enter image description here

\documentclass{article}
\usepackage{amsmath}

\begin{document}
\[
    f(x)= 
\begin{cases}
    \frac{x^2-x}{x},& \text{if } x\geq 1\\
    0,              & \text{otherwise}
\end{cases}
\]
\end{document}

or if you would prefer a displaystyle fraction, then you could use dcases from the mathtools package, which extends (and loads) the amsmath package.

enter image description here

\documentclass{article}
\usepackage{mathtools}

\begin{document}
\[
    f(x)= 
\begin{dcases}
    \frac{x^2-x}{x},& \text{if } x\geq 1\\
    0,              & \text{otherwise}
\end{dcases}
\]
\end{document}
2
  • I had thought you usually want a \, before text punctuation inline with math, no?
    – Translunar
    Sep 12 '17 at 14:56
  • Is it possible to change the curly braces to bracket in this environment? Sep 19 '17 at 7:31
39

Just for the sake of completeness (i.e. environments where amsmath may not be available): There is a pseudo-parenthesis . that can be used to terminate an opening parenthesis:

\documentclass{standalone}

\begin{document}

$\left\{ 
  \begin{array}{ c l }
    \frac{x^2 - x}{2} & \quad \textrm{if } x \geq 1 \\
    0                 & \quad \textrm{otherwise}
  \end{array}
\right.$

\end{document}

Output:

enter image description here

5
  • 10
    You should expand this answer to show how to use this to produce the output in the original image. Mar 10 '12 at 1:04
  • 5
    @PeterGrill: Well, there are ways, but cases and dcases are much much more suitable for this task. Are there conditions where these environments are not available?
    – krlmlr
    Mar 10 '12 at 5:48
  • 2
    I actually like your answer better.
    – 0rkan
    Sep 25 '15 at 3:09
  • I like this answer for its flexibility. It shows how to create a single-sided brace (or any other grouping symbol) for applications where cases isn't suitable.
    – drmuelr
    Oct 13 '18 at 5:31
  • @krlmlr I have found environments where I don't have access to the amsmath package, so expanding this to perform what the question asked for would certainly help me! Jan 25 at 16:26

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