How to write conditional equations with one-sided curly brackets

Question

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?

use cases or dcases. – Peter Grill Mar 07 '12 at 20:05 — Peter Grill, Mar 07 '12 at 20:05

score 305 · Accepted Answer · edited Feb 17 '17 at 15:34

305

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}

edited Feb 17 '17 at 15:34

barbara beeton

88,848

answered Mar 07 '12 at 20:06

cmhughes

100,947

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? – Hosein Rahnama Sep 19 '17 at 07:31

score 50 · Answer 2 · edited Jul 15 '21 at 22:44

50

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:

edited Jul 15 '21 at 22:44

Werner

603,163

answered Mar 09 '12 at 21:16

krlmlr

12,530

11

You should expand this answer to show how to use this to produce the output in the original image. – Peter Grill Mar 10 '12 at 01:04
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 05:48
3

I actually like your answer better. – 0rkan Sep 25 '15 at 03:09
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 05:31
@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 '21 at 16:26

How to write conditional equations with one-sided curly brackets

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