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I need to have an arrow that has a vertical bar in the middle, something like this:

----|---->

in commutative diagrams. Tikzcd does not have such an arrow supported directly, as far as I can tell.

Any ideas on how to do this? Ideally I would like to still be able to have labels.

I found a way to do this in the math environment using \mathclap and + as shown in code for arrow with a short vertical line in the middle of the shaft (not perfect but good enough) but this does not work well within a commutative diagram.

1 Answer 1

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tikz-cd supports markings.

\documentclass{article}
\usepackage{tikz-cd}
\begin{document}
\begin{tikzcd}[]
    a \arrow[r,"|" marking] & b
\end{tikzcd}
\end{document}

enter image description here

If you want to have full control over all aspects of the bar, you can use a TikZy decoration.

\documentclass{article}
\usepackage{tikz-cd}
\usetikzlibrary{decorations.markings}
\tikzset{mid vert/.style={/utils/exec=\tikzset{every node/.append style={outer sep=0.8ex}},
postaction=decorate,decoration={markings,
mark=at position 0.5 with {\draw[-] (0,#1) -- (0,-#1);}}},
mid vert/.default=0.75ex}
\begin{document}
\begin{tikzcd}[]
    a \arrow[r,mid vert,"pft"] & b \arrow[r,"pht"] & c
\end{tikzcd}
\end{document}

enter image description here

In this version, the parameter is the length of the arrow, with the default being 2*0.75ex, but you can adjust the other parameters as well.

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  • Great this works! Is it possible to add to the definition of mid vert the fact that all the labels should have outer sep of, say, 0.8ex? I am not familiar with decorations
    – geguze
    May 29, 2019 at 4:29
  • @geguze Yes, it is. (I actually like the idea!) I modified the code accordingly. (And this change is only local, as shown in the example, i.e. the other arrows will have business as usual.)
    – user121799
    May 29, 2019 at 4:40
  • Wonderful! One last question. The definition of the arrow with a bar in running math, suggested at the link included in my question, does not look very good, especially when compared to a tikz-cd diagram. Any suggestion on how to make that better? One could put a tikz-cd inline based on the mid vert definition you provided, not sure that's the best way though.
    – geguze
    May 29, 2019 at 4:51
  • 1
    @geguze How about $a\mathrel{\tikz[baseline=-0.5ex]{\draw[->,mid vert](0,0) --(1.2em,0);}}b\longrightarrow c$ with the above preamble? Or \newcommand{\tobar}{\mathrel{\tikz[baseline=-0.5ex]{\draw[->,mid vert](0,0) --(1.2em,0);}}} $a\tobar b\longrightarrow c$? There is a long discussion how to make this symbol adjust to the font size, see this thread. (For a simple vertical bar you could also use \rule ...)
    – user121799
    May 29, 2019 at 4:57

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