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Question

I am trying to compile tree diagrams using the mptrees package (I like this) with LuaLaTeX and luamplib. On TeX Stack Exchange, I found only one question on this topic,

background color with \mpcolor

but it does not clarify what minimal code is required to compile the drawings of mptrees package to compile correctly.

I have downloaded the mptrees package's ZIP file and I am trying to understand what to add or remove to the following code to get the tree diagrams to compile successfully, starting from:

\documentclass[10pt]{article}
\begin{document}
\mplibforcehmode
\begin{exampleblock}{}\centering
    \extractcolorspecs{block body example.bg}\modelcmd\colorcmd
    \begin{mplibcode}
      input mptrees;
      beginfig(1)
      dirtree:=-90;
      typeprob:=2;
      background:=(\colorcmd);
      draw tree[1][1](1.25cm,5cm)("P","$\frac{1}{2}$","F","$\frac{1}{2}$");
      draw tree[2][1](1.25cm,1.5cm)("R","$\frac{1}{5}$","B","$\frac{1}{5}$","N","$\frac{3}{5}$");
      draw tree[2][2](1.25cm,1.5cm)("R","$\frac{1}{5}$","B","$\frac{1}{5}$","N","$\frac{3}{5}$");
      endfig;
    \end{mplibcode}
  \end{exampleblock}
\end{document}

Hence:

What is the minimal working example (MWE) to get the mptrees drawings to compile?

Any guidance or example codes would be greatly appreciated.

Answer 1

You have not loaded luamplib to use mplib commands, and the example block is a beamer command you haven't defined. here I just set the color using three rgb values

\documentclass[10pt]{article}
\usepackage{luamplib}
\begin{document}
\mplibforcehmode
%\begin{exampleblock}{}\centering
%    \extractcolorspecs{block body example.bg}\modelcmd\colorcmd
    \begin{mplibcode}
      input mptrees;
      beginfig(1)
      dirtree:=-90;
      typeprob:=2;
      background:=(.7,.5,0);
      draw tree[1][1](1.25cm,5cm)("P","$\frac{1}{2}$","F","$\frac{1}{2}$");
      draw tree[2][1](1.25cm,1.5cm)("R","$\frac{1}{5}$","B","$\frac{1}{5}$","N","$\frac{3}{5}$");
      draw tree[2][2](1.25cm,1.5cm)("R","$\frac{1}{5}$","B","$\frac{1}{5}$","N","$\frac{3}{5}$");
      endfig;
    \end{mplibcode}
%  \end{exampleblock}
\end{document}

Answer 2

The exampleblock environment and the block body example.bg colour are beamer specific things. They will work if you use the beamer class like in the linked answer:

% !TeX TS-program = lualatex -interaction=nonstopmode % | txs:///view-pdf | txs:///view-log
\documentclass[10pt]{beamer}
\usepackage{luamplib}
\usecolortheme{orchid}
\begin{document}
\mplibforcehmode
\begin{frame}
  \begin{exampleblock}{}\centering
    \extractcolorspecs{block body example.bg}\modelcmd\colorcmd
    \begin{mplibcode}
      input mptrees;
      beginfig(1)
      dirtree:=-90;
      typeprob:=2;
      background:=(\colorcmd);
      draw tree[1][1](1.25cm,5cm)("P","$\frac{1}{2}$","F","$\frac{1}{2}$");
      draw tree[2][1](1.25cm,1.5cm)("R","$\frac{1}{5}$","B","$\frac{1}{5}$","N","$\frac{3}{5}$");
      draw tree[2][2](1.25cm,1.5cm)("R","$\frac{1}{5}$","B","$\frac{1}{5}$","N","$\frac{3}{5}$");
      endfig;
    \end{mplibcode}
  \end{exampleblock}
\end{frame}
\end{document}