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

enter image description here

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!

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1 Answer 1

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Like this?

enter image description here

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}
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  • Thank you, that works. For my own taste, I inserted a \big before the \vert.
    – Seub
    Jun 24, 2017 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, 2017 at 5:32
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    @Mico: Perfect, thank you! So, for those interested, I did: \newcommand{\evalat}[1]{_{\mbox{${\mkern1.5mu}\big\vert_{#1}$}}}
    – Seub
    Jun 24, 2017 at 18:48
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    @Seub - You may also want to give \newcommand\evalat[1]{_{\mkern1.5mu\big\vert_{\scriptstyle #1}}} a try.
    – Mico
    Jun 24, 2017 at 19:07
  • @Mico Yep, I'm keeping your suggestion!
    – Seub
    Jun 24, 2017 at 20:01

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