Take the 2-minute tour ×
TeX - LaTeX Stack Exchange is a question and answer site for users of TeX, LaTeX, ConTeXt, and related typesetting systems. It's 100% free, no registration required.

I'd like to generate PDF's for some ad hoc screenshots, but I'm getting an undefined control error. I tried \usepackage{amsmath} after the line \usepackage{pgfplots} but that didn't work. I thought maybe that package was required for use of \frac{x}{2}

I'm using TeXworks with the following to try and generate a generic plot of x/2:

\documentclass{article}
\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}[>=stealth]
    \begin{axis}[
        xmin=-10,xmax=10,
        ymin=-10,ymax=10,
        axis x line=middle,
        axis y line=middle,
        axis line style=<->,
        xlabel={$x$},
        ylabel={$y$},
        ]
        \addplot[no marks,blue,<->] expression[domain=-10:10,samples=100]{\frac{x}{2}} 
                    node[pos=0.65,anchor=south west]{$y=\frac{x}{2}$}; 
    \end{axis}
\end{tikzpicture}
\end{document}

The error is on the node line 16 I believe, but I can't tell if it's syntax or otherwise.

! Undefined control sequence.
\pgfmath@dimen@ ...men@@ #1=0.0pt\relax \pgfmath@ 

l.16 ...=0.65,anchor=south west]{$y=\frac{x}{2}$};

Please consider me very new to LaTeX. I guess I'm assuming there is a missing package, since I can successfully plot simple linear graphs that don't include \frac.

share|improve this question
    
I realized as I was reading John's answer that the node was the annotation and should use \frac while the plot should be the generic expression. –  David Jun 4 '13 at 16:13

1 Answer 1

up vote 8 down vote accepted

You should write x/2 instead of \frac{x}{2}.

  • In the equation of the graph, you want a mathematical expression that PGFplots can understand. The syntax for division in PGFplots is simply /.
  • In the label for the graph, you just want a piece of text, so y=\frac{x}{2} is fine here.

Fixed code

\documentclass{article}
\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}[>=stealth]
    \begin{axis}[
        xmin=-10,xmax=10,
        ymin=-10,ymax=10,
        axis x line=middle,
        axis y line=middle,
        axis line style=<->,
        xlabel={$x$},
        ylabel={$y$},
        ]
        \addplot[no marks,blue,<->] expression[domain=-10:10,samples=100]{x/2} 
                    node[pos=0.65,anchor=south west]{$y=\frac{x}{2}$}; 
    \end{axis}
\end{tikzpicture}
\end{document}

enter image description here

share|improve this answer
    
I see--the node is the annotation which is essentially text while the addplot is the expression. –  David Jun 4 '13 at 16:14

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.