Why does \addplot shift my graph of a \pgfmathdeclarefunction function to the right?

Question

When plotting a \pgfmathdeclarefunctioned function the graph gets an offset to the right that is proportional to the number of times the function is called in the formula.

I have boiled my initial code down to following example, which exhibits the behaviour:

\documentclass[12pt]{scrbook}
\usepackage{tikz,pgfplots}
\begin{document}
    \pgfmathdeclarefunction{f}{1}{ \pgfmathparse{#1 * #1} }
    \begin{figure}
        \centering
        \begin{tikzpicture}
            \begin{axis}
                \addplot {x + 2 * x * x}; %no shift (clearly centered
                %\addplot {x + 2 * f(x)}; %little shift to the right
                %\addplot {x + f(x) + f(x)}; %shifted nearly off the sheet
            \end{axis}
        \end{tikzpicture}
    \end{figure}
\end{document}

In this example it is obviously easy to write the function inside the \addplot command. But I have a more complex function which is used all over the place and shifts my plots off the page.

I am pretty new to LaTex and probably did an error somewhere, but I can't find it. So what is wrong with this?

Answer 1

That's because you have spurrious spaces in your function definition. Get rid of them and the problem is solved:

\documentclass[12pt]{scrbook}
\usepackage{tikz,pgfplots}
\begin{document}
    \pgfmathdeclarefunction{f}{1}{%
        \pgfmathparse{#1*#1}%
    }
    % or \pgfmathdeclarefunction{f}{1}{\pgfmathparse{#1*#1}}
    \begin{figure}
        \centering
        \begin{tikzpicture}
            \begin{axis}
                \addplot {x + 2 * x * x}; %no shift (clearly centered
                \addplot {x + 3 * f(x)}; %little shift to the right
                \addplot {x + f(x) + f(x) + f(x) + f(x)}; %shifted nearly off the sheet
            \end{axis}
        \end{tikzpicture}
    \end{figure}
\end{document}