[Tex/LaTex] Vertical bar for “evaluated at”

delimitersmath-modesubscriptssymbols

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!

Best Answer

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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