Doing math inside of pgfplotsset

Question

I am declaring an environment to help with drawing binomial distributions. One of the natural parameters to give to such a function is "n", the number of trials. My plotting function, however, needs to plot 0 .. n-1 samples. I am finding that I am unable to do the "-1" within a pgfplotsset. Can anyone help me do this? MWE:

\documentclass{minimal}

\usepackage{pgfplots}

\newenvironment{BinomDist}[1]{%                                                 
  \pgfplotsset{DistAxis/.style={%                                               
      samples at={0,...,#1} % Want this to say ``#1-1'' or equiv.               
    }
  }
}{}

\begin{document}

\begin{BinomDist}{8}
  \begin{tikzpicture}
    \begin{axis}[DistAxis]
      \addplot [draw=black] {x};
    \end{axis}
  \end{tikzpicture}
\end{BinomDist}

\end{document}

score 3 · Accepted Answer · answered Jan 26 '20 at 03:37

This is very simple: samples at={0,...,\the\numexpr#1-1}.

\documentclass{article}
\usepackage{pgfplots}
%\pgfplotsset{compat=1.16} %<-consider using this
\newenvironment{BinomDist}[1]{%                                                 
  \pgfplotsset{DistAxis/.style={%                                               
      samples at={0,...,\the\numexpr#1-1} 
    }
  }
}{}

\begin{document}

\begin{BinomDist}{8}
  \begin{tikzpicture}
    \begin{axis}[DistAxis]
      \addplot [draw=black] {x};
    \end{axis}
  \end{tikzpicture}
\end{BinomDist}

\end{document}

BTW, please consider not to use the minimal class, and to indicate the version.

For more complicated cases you might want to use code with \pgfmathtruncatemacro.

\documentclass{article}
\usepackage{pgfplots}
\pgfplotsset{compat=1.16} %<-consider using this
\newenvironment{BinomDist}[1]{%                                                 
  \pgfplotsset{DistAxis/.code={%   
    \pgfmathtruncatemacro{\iMax}{pow(2,#1-1)}%
     \pgfplotsset{samples at={0,...,\iMax}}%
    }
  }
}{}

\begin{document}

\begin{BinomDist}{8}
  \begin{tikzpicture}
    \begin{axis}[DistAxis]
      \addplot [draw=black] {x};
    \end{axis}
  \end{tikzpicture}
\end{BinomDist}
\end{document}

Why is using the minimal environment a poor choice? I thought it existed for situations like this where I want to create an example with the simplest possible environment so that the situation is focused on the issue. I was following the guidance here: https://tex.stackexchange.com/questions/20974/what-is-the-advantage-of-using-minimal-over-article-when-creating-a-standalone-g where the answer suggests using minimal for MWE's. — Christopher Donham, Jan 26 '20 at 03:49
@ChristopherDonham My worries can be found under this thread. While I do not think that for the current example these concerns are too important, I feel that the reasons mentioned there are enough motivation to try to avoid propagating this class more than necessary. — , Jan 26 '20 at 03:52

Doing math inside of pgfplotsset

1 Answers1