[Tex/LaTex] 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: