Create Table for a Family of Curves

Question

Following the issue Color Management with a Family of Curves I couldn't find a proper way of creating the associated table for a family of curves.

I tried to create new columns with respect to the parameter \y (exponent), but without success using \foreach or \pgfplotsinvokeforeach (see comment lines).

Here is the code:

\documentclass[border=1mm]{standalone}
\usepackage{pgfplotstable}
\pgfplotsset{compat=1.8}

\pgfplotstableread{
1   1
2   4
3   9
4   16
5   25
}\dataQuad

\begin{document}
    \begin{minipage}[c]{0.75\textwidth}
        \begin{tikzpicture}
            \begin{axis}[%
                legend pos=north west,
                domain=0:5,
                cycle list name=color,
                xlabel=${x}$,
                ylabel=${y}$]
            \addplot [smooth] table[x index=0, y index=1] {\dataQuad};
            \legend{$y=x^2$}
            \foreach \y/\c in {3/green,4/red,5/brown}{%
                \edef\temp{\noexpand\addplot [color=\c,smooth] table[x index=0, y expr=\noexpand\thisrowno{0}^\y] {\noexpand\dataQuad};}
            \temp
            \addlegendentryexpanded{$y=x^\y$}
            }
            \end{axis}
        \end{tikzpicture}
    \end{minipage}
%
    \begin{minipage}[c]{0.75\textwidth}
        \pgfplotstablecreatecol[
            create col/assign/.code={%
                \foreach \y in {3,4,5} {%
%                   \pgfplotsinvokeforeach{3,4,5} {%
                    \pgfmathparse{\thisrow{1}*\y}
%                   \thisrow{1}*#1
                }
            \pgfkeyslet{/pgfplots/table/create col/next content}\pgfmathresult
            }
        ]{exp}\dataQuad
        \pgfplotstabletypeset[columns={[index]0,[index]1,exp}]\dataQuad
    \end{minipage}
\end{document}

What goes wrong here? Additionally, a header for each column with reference to each list entry from '{3,4,5}' would be great.

Thanks again, Paul

---

OK, the error '! Package PGF Math Error: Sorry, an internal routine of the floating point unit' from above occurs when defining a list with \newcommand{\param}{2,3,4,5}, see following MWE:

\documentclass[border=1mm]{standalone}
\usepackage{pgfplotstable}
\pgfplotsset{compat=1.8}

\pgfplotstableread{
1
2
3
4
5
}\dataQuad

\newcommand{\param}{2,3,4,5}

\pgfplotsforeachungrouped \y in \param {%
    \pgfplotstablecreatecol[
        create col/expr={\thisrow{0}^\y}
    ]{\y}\dataQuad
}

\begin{document}
    \begin{minipage}[c]{0.75\textwidth}
        \begin{tikzpicture}
            \begin{axis}[%
                legend pos=north west,
                domain=0:5,
                cycle list={green, red, black, purple, orange},
                xlabel=${x}$,
                ylabel=${y}$]
            \pgfplotsinvokeforeach{2,...,5}{
                    \addplot +[smooth] table [x index=0, y=#1] \dataQuad;
            }
            \end{axis}
        \end{tikzpicture}
    \end{minipage}

    \begin{minipage}[c]{0.75\textwidth}
        \pgfplotstabletypeset\dataQuad
    \end{minipage}
\end{document}

Do I have to use another approach for predefine a list?

Thanks, Paul

Answer 1

If I understand your question correctly, you want to create one column for each exponent, and in that column, the content of the first column in the table should be raised to the power of the current column index.

For that, you can loop over the desired exponents, and run \pgfplotstablecreatecol each time. Note that it's much easier to use create col/expr than create col/assign (the latter is a really powerful general purpose method, but if all you want is a mathematical expression, expr is the way to go).

\documentclass[border=1mm]{standalone}
\usepackage{pgfplotstable}
\pgfplotsset{compat=1.8}

\pgfplotstableread{
1
2
3
4
5
}\dataQuad

\pgfplotsforeachungrouped \y in {2,...,5}{
    \pgfplotstablecreatecol[
        create col/expr={\thisrow{0}^\y}
    ]{\y}\dataQuad
}

\begin{document}
    \begin{minipage}[c]{0.75\textwidth}
        \begin{tikzpicture}
            \begin{axis}[%
                legend pos=north west,
                domain=0:5,
                cycle list={green, red, black, purple, orange},
                xlabel=${x}$,
                ylabel=${y}$]
            \pgfplotsinvokeforeach{2,...,5}{
                    \addplot +[smooth] table [x index=0, y=#1] \dataQuad;
            }
            \end{axis}
        \end{tikzpicture}
    \end{minipage}

    \begin{minipage}[c]{0.75\textwidth}
        \pgfplotstabletypeset\dataQuad
    \end{minipage}
\end{document}