237

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?

Improve this question
1
  • 4
    use cases or dcases.
    – Peter Grill
    Mar 7, 2012 at 20:05

2 Answers 2

Reset to default
297

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}
Improve this answer
2
  • I had thought you usually want a \, before text punctuation inline with math, no?
    – Translunar
    Sep 12, 2017 at 14:56
  • Is it possible to change the curly braces to bracket in this environment?
    – Hosein Rahnama
    Sep 19, 2017 at 7:31
48

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

Improve this answer
5
  • 11
    You should expand this answer to show how to use this to produce the output in the original image.
    – Peter Grill
    Mar 10, 2012 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, 2012 at 5:48
  • 3
    I actually like your answer better.
    – 0rkan
    Sep 25, 2015 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, 2018 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!
    – Connor McCormick
    Jan 25, 2021 at 16:26

Not the answer you're looking for? Browse other questions tagged .