# Vertical bar for “evaluated at”

I would like to create a vertical "evaluation" bar similar to the one in this formula:

This was produced by the code:

df\,_{\big\rvert x} \colon T_x M \to T_y N


It comes close to what I want, but I am not entirely satisfied: I would like the 'x' to be lower (e.g. aligned with the bottom of the vertical bar). Also maybe have the vertical bar slightly less tall.

Suggestions? Thank you!

Like this?

To get the vertical bar a bit larger, you can use \raisebox. This way, the \vert will be in the normal math size and x will be in the \scriptsize style. Alternatively, you can use \mbox if you don't like \raisebox. In this case, the usual font sizes can be used (tiny, scriptsize, footnotesize, small, normalsize, large, Large, LARGE, huge, Huge).

\documentclass{article}
\usepackage{amsmath,mathptmx}
\begin{document}

$df\,\raisebox{-.5em}{\vert_{x}} \colon T_x M \to T_y N$
%
$df\,_{\mbox{\vert_{x}}} \colon T_x M \to T_y N$

\end{document}

• Thank you, that works. For my own taste, I inserted a \big before the \vert. – Seub Jun 24 '17 at 2:17
• +1. Two suggestions. First, consider moving the \, directive inside the argument of \raisebox or \mbox. Second, \, may provide to much whitespace; consider inserting half as much whitespace by issuing the directive \mkern1.5mu instead. – Mico Jun 24 '17 at 5:32
• @Mico: Perfect, thank you! So, for those interested, I did: \newcommand{\evalat}[1]{_{\mbox{${\mkern1.5mu}\big\vert_{#1}$}}} – Seub Jun 24 '17 at 18:48
• @Seub - You may also want to give \newcommand\evalat[1]{_{\mkern1.5mu\big\vert_{\scriptstyle #1}}} a try. – Mico Jun 24 '17 at 19:07
• @Mico Yep, I'm keeping your suggestion! – Seub Jun 24 '17 at 20:01