symbols
I have the following expression
$$\left\{\varphi\in\text{End}\left({\widetilde{E}/\overline{\F}_{\Pf}}\right)\mid \varphi\text{Frob}_{\Pf}=\text{Frob}_{\Pf}\varphi\right\}$$
and would like to know how to match the length of \mid to the length of \left\{ and \right\}. Thanks!
Try
\left.\frac{\partial f}{\partial x}\right|_{x_0}
Or if you have \usepackage{amsmath}, you can use \rvert instead of the |. In fact, this is probably the better way to go.
If you want to get \middle| to behave exactly as \mid on all accounts (spacing, stacking in the form \mid\mid, etc.), you need to use \mathrel{} on both sides of \middle| (manual spaces like \; won't do the job correctly in all situations):
\newcommand{\relmiddle}[1]{\mathrel{}\middle#1\mathrel{}}
Here's a code that compares \mid and the new command \relmiddle on two different formulas and shows that the spacing is identical:
\documentclass{article}
\newcommand{\relmiddle}[1]{\mathrel{}\middle#1\mathrel{}}
\begin{document}
\nulldelimiterspace=0pt% to kill the little space before \left and after \right (not a good idea in a real document)
$a \mid -b$\par
$\left. a \relmiddle| -b \right.$
$a \mid\mid -b$\par
$\left. a \relmiddle|\relmiddle| -b \right.$
\end{document}
Best Answer
For middle stretchable delimiters you can use
\middle:Notice also the use of
\DeclareMathOperatorto produce the right font and spacing for "End" and "Frob". Also,$$...$$shouldn't be used in modern LaTeX documents; use\[...\]instead. Since I didn't know the definitions of some commands, I defined them provisionally.