3
\documentclass{beamer}
\usepackage{amsmath} 
\usepackage{tikz-cd}

\begin{document}
\begin{frame}[fragile, t]{My slides}
\only<1>{
\begin{equation*}
\begin{tikzcd}
a 
\end{tikzcd}
\end{equation*}}
\only<2>{
\begin{equation*}
\begin{tikzcd}
a  \arrow{r} &  b
\end{tikzcd}
\end{equation*}}
\end{frame}
\end{document}

All I want is to show 'a' first, then a point to b, like this 'a->b' (and it has to use Tikz-cd!). But Tikzcd is making it impossible because I get the following error:

Package pgf Error: Single ampersand used with wrong catcode.

See the pgf package documentation for explanation. Type H for immediate help. ...
l.13 \end{equation*}} This error message was generated by an \errmessage command, so I can't give any explicit help. Pretend that you're Hercule Poirot: Examine all clues, and deduce the truth by order and method.

Is there any way to solve this issue? The & works fine when it is on its own frame. But when I put it into a \only block things go bonkers.

I thought [fragile] was supposed to prevent these things!

1 Answer 1

5

Normal ampersand (&) does not work well with beamer, so you have to change it. I change to \&.

\documentclass{beamer}
\usepackage{amsmath} 
\usepackage{tikz-cd}

\begin{document}
\begin{frame}[fragile, t]{My slides}
\only<1>{
\begin{equation*}
\begin{tikzcd}
a 
\end{tikzcd}
\end{equation*}}
\only<2>{
\begin{equation*}
\begin{tikzcd}[ampersand replacement=\&]
a  \arrow{r} \&  b
\end{tikzcd}
\end{equation*}}
\end{frame}
\end{document}
5
  • Great. Thanks. I didn't try that solution because I thought this was for the case when you actually want to write an ampersand. I thought Tikzcd is using that ampersand as an anchor to the next node
    – Concu Bine
    May 20, 2019 at 8:03
  • @Themanofyourdream TikZ-cd is, literally, a TikZ matrix, nothing more.
    – user156344
    May 20, 2019 at 8:03
  • I'm guessing that the & issue here comes from the fact that the tikzcd is being used inside a macro and that closses the catcodes prematurely.
    – daleif
    May 20, 2019 at 10:01
  • @daleif I have very little knowledge with beamer, so I can't explain it fully. But after some issues I had to deal with, and looking at some questions here, I found that & and beamer are not friends.
    – user156344
    May 20, 2019 at 10:43
  • @JouleV it has nothing to do with beamer, try wrapping an tikzcd env in the following command: \newcommand\test[1]{#1} you get the same issue, and the same solution.
    – daleif
    May 20, 2019 at 11:37

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