Sizing for 'given that' symbol - vertical bar

Question

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.

Answer 1

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.

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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:

Answer 2

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

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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}

Answer 3

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}

Answer 4

Use \left.\right|

For example $$\mathbb{E}(Y^3) = \left.\frac{d^3 M_Z(t)}{d t^3}\right|_{t=0}$$