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When I make presentations (with beamer), I like to have a bar along the bottom showing progress through the presentation visually. The interesting bit of the code below is the division on the node[fill=navfg,...] line:

\usebeamercolor{palette primary}
    \tikz\draw[text height=2*\navradius,inner sep=0ex,rounded corners=\navradius]
        node[fill=navbg,minimum width=\textwidth-\navradius](back){} (back.west)
        node[fill=navfg,minimum width=(\insertframenumber-1)/(\inserttotalframenumber-1)*(\textwidth-\navradius),right]{}
        (back.south) node[below]{}

This works great, except during the first attempt to build a presentation using this snippet. During the first build, \inserttotalframenumber has the value 1, so this makes a division by zero. The obvious fix is to use max:

node[fill=navfg,minimum width=(\insertframenumber-1)/max(1,\inserttotalframenumber-1)*(\textwidth-\navradius),right]{}

But this results in an error:

! Missing \endcsname inserted.
<to be read again> 
l.10 \begin{document}

!  ==> Fatal error occurred, no output PDF file produced!

Why do I get this error? What can I do to solve this problem correctly?

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up vote 4 down vote accepted

If TikZ doesn't want to evaluate some expression correctly, you can often help it by surrounding the expression with braces. In your case,

node[fill=navfg,minimum width={(\insertframenumber-1)/max(1,inserttotalframenumber-1)*(\textwidth-\navradius)},right]{}

works correctly.

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While that does make the errors disappear, it unfortunately also makes the navigation bar disappear. – Daniel Wagner Jul 20 '12 at 1:06
It works for me. Maybe you could add a complete MWE. – Caramdir Jul 20 '12 at 1:07
Whoops, you're right, this works perfectly. My PDF viewer was just cutting off the bottom of each page during the test. – Daniel Wagner Jul 20 '12 at 1:10

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