# Sizing for 'given that' symbol - vertical bar

I want to write an equation with $\mid$, but it is too small, can i make it bigger in any way?

I am kinda new to TeX so i have no idea how to do it.

• Perhaps How can you address the size of surrounding parentheses whose size is determined by \left and \right? can help... not sure about the usage of \mid in your case. More detail? – Werner Oct 31 '13 at 4:36
• Well, \Bigm| would help? And what exactly do you need it for (because there're at least 5 different meanings of |)? Maybe you can help us in helping you by providing a Minimal (non-)Working Example... – yo' Oct 31 '13 at 7:37
• Are you sure that you want \mid (which is usually used to such that meaning) or do you want a vertical bar to denote the absolute value, for example, on a fraction? If you want the second option, use \left|...\right|. – Sigur Oct 31 '13 at 10:57
• I'm not sure to have ever heard of a "given that" symbol. Can you show what it is and a context where it's used? – egreg Oct 31 '13 at 15:14
• @egreg: I took it to mean conditional probability, e.g., P(X = x|Y = y). – alexwlchan Nov 2 '13 at 8:59

2017 Update: Since \mid is a relation, under normal circumstances the spaces manually inserted around \middle| should be thick \; instead of thin \,. See table on p.170 of the TEXbook.

Instead of \mid, you can use \middle command to enlarge vertical delimiter and insert spaces manually, here is an example:

\documentclass{article}

\usepackage{mathtools}

\begin{document}
$S=\left(\frac{\sum_{i=1}^{n}X_i}{n}\;\middle|\;X_i\sim\chi^2(k)\right)$
$\left.\frac{\sum_{i=1}^{n}X_i+Y_i}{n}\;\middle|\;X\sim\chi^2_k\;\middle|\;Y\sim\mathcal{N}(\mu,\sigma^2)\right.$

\end{document}


Result:

Better yet, we can make a custom command for our conveniences:

\makeatletter
\newcommand{\@giventhatstar}[2]{\left(#1\;\middle|\;#2\right)}
\newcommand{\@giventhatnostar}[3][]{#1(#2\;#1|\;#3#1)}
\newcommand{\giventhat}{\@ifstar\@giventhatstar\@giventhatnostar}
\makeatother


It works sorta like \DeclarePairedDelimiter in mathtools, for example:

$\giventhat{f(x)=\frac{x^2}{2}}{x=1,2,3,\dotsc}$
$\giventhat[\big]{f(x)=\frac{x^2}{2}}{x=1,2,3,\dotsc}$
$\giventhat[\Big]{f(x)=\frac{x^2}{2}}{x=1,2,3,\dotsc}$
$\giventhat*{f(x)=\frac{x^2}{2}}{x=1,2,3,\dotsc}$


will give you:

• \cdots is not the proper dots to use here – daleif Nov 1 '13 at 7:30

Sounds like conditional probability. In that case I usually recommend our students to use something similar to

\newcommand\given[1][]{\:#1\vert\:}


Which will be manually scalled via, say

\given[\Big]


Then the code makes sense when read

ADDITION. Building further on Francis' suggestion \given can be build into his macros such that the macros only takes one argument.

\documentclass[a4paper]{memoir}
\usepackage{mathtools}
\newcommand\givenbase[1][]{\:#1\lvert\:}
\let\given\givenbase
\newcommand\sgiven{\givenbase[\delimsize]}
\DeclarePairedDelimiterX\Basics[1](){\let\given\sgiven #1}
\newcommand\Average{E\Basics}
\begin{document}
\begin{align*}
\Basics{X} \qquad \Basics[\Big]{ X \given Y}\\
\Average{X} \qquad \Average[\Big]{ X \given Y}\\
\end{align*}
\end{document}


• Maybe \operatorname{E} instead of E? – Francis Nov 1 '13 at 8:54
• It might be yes. Though I think most people think of it in the same manner as f(x), i.e. just a function. Some people use an upright E, some people even use \mathbb{E}. Depends on the tradition. – daleif Nov 1 '13 at 9:45

This uses features of the scalerel package.

\documentclass{article}
\usepackage{scalerel}
\begin{document}
\noindent You can stretch it to a size:\\
$A \mid \mathrel{\stretchto{\mid}{3ex}} \mathrel{\stretchto{\mid}{4ex}} B$\\
or you can stretch it to fit something else:\\
$\stretchrel{\mid}{\displaystyle\frac{A}{B}}$\\
\end{document}