Decorating path with math symbols causes pdflatex to hang?

Question

I need to decorate a path with some text that includes math symbols. I followed this example, which works fine as long as I only include text. Here is the MWE (minor changes compared to example to replace \def\myshift by raise=):

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{decorations.text}

\begin{document}

\begin{tikzpicture}
\node (One) at (-3,0) [shape=circle,draw] {$One$}; 
\node (Two) at (3,0) [shape=circle,draw] {$Two$};
\draw [->,thick,postaction={decorate,decoration={text along path,text align=center,raise=2pt,text={$b$}}}] (One) to [bend right=45]  (Two);
\draw [->,thick,postaction={decorate,decoration={text along path,text align=center,raise=-7pt,text={$a$}}}] (One) to [bend left=45] (Two);
\end{tikzpicture}

\end{document}

However, as soon as I replace a by \alpha (as an example), the MWE does not compile anymore. It seems to hang and when I interrupt it with ctrl-C, I get:

! Interruption.
<to be read again> 
                   \let 
l.12 ...\alpha$}}}] (One) to [bend left=45] (Two);

(I'm running pdfTeX, Version 3.14159265-2.6-1.40.20 (TeX Live 2019).)

@Schrödinger's cat: I updated my MacTeX distribution before posting, so I'm also using the latest available version (log file shows Package: pgf 2019/12/21 v3.1.5a (3.1.5a)). Maybe my post is confusing - since the MWE I posted is the code that works, but it breaks if I change a to \alpha? — user1362373, Dec 31 '19 at 17:13

score 2 · Accepted Answer · answered Dec 31 '19 at 17:14

Put braces around the macros. Why? Because in the manual v3.1.5 on p. 659 it says

Once I add braces, there is no problem.

\documentclass{standalone}

\usepackage{tikz}
\usetikzlibrary{decorations.text}

\begin{document}

\begin{tikzpicture}
\node (One) at (-3,0) [shape=circle,draw] {$One$}; 
\node (Two) at (3,0) [shape=circle,draw] {$Two$};
\draw [->,thick,postaction={decorate,decoration={text along path,text
align=center,raise=2pt,text={${\beta}$}}}] (One) to [bend right=45]  (Two);
\draw [->,thick,postaction={decorate,decoration={text along path,text
align=center,raise=-7pt,text={${\alpha}$}}}] (One) to [bend left=45] (Two);
\end{tikzpicture}

\end{document}

Alain Matthes · Answer 2 · 2019-12-31T18:32:29.210

Not exactly an answer ... Always in my list of packages for the math teacher, this one is called tkz-graph. You need to know some options from TikZ.

\documentclass[border=.25cm]{standalone}
\usepackage{tkz-graph}

\begin{document}
 \begin{tikzpicture}
   \SetGraphUnit{4}
   \Vertex{One}
   \EA(One){Two}
   \Edge[style={<-,bend left},labelstyle={above},label=$\beta$](Two)(One) 
   \Edge[style={<-,bend right},labelstyle={below},label=$\alpha$](Two)(One)
\end{tikzpicture}
\end{document}

With one line of code you get the graph below (if you need probability graph or example of graph theory)

\documentclass[border=.25cm]{standalone}
\usepackage{tkz-graph}
\begin{document}
\begin{tikzpicture}
  \grProb{A}{B}{NO}{SO}{WE}{EA}
\end{tikzpicture}
\end{document}

Decorating path with math symbols causes pdflatex to hang?

2 Answers2