How to LaTeX the graph of a permutation?

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Slightly annoying indeed: the show method for a permutation

• computes a graph corresponding to that permutation
• displays it
• but does not return it

Instead it returns nothing, which in Python amounts to returning None.

That method should be decomposed into a method that provides the graph and a method that shows it.

Here is a workaround until such a method is provided.

One can check what the show method does by inspecting the source code:

sage: p = Permutation([3, 1, 2])
sage: p.show??

This helps us figure out how to produce the graph.

sage: p = Permutation([3, 1, 2])
sage: g = DiGraph([(i+1, p[i]) for i in range(len(p))], loops=True)
sage: g
Looped digraph on 3 vertices

Now we can get the LaTeX TikZ code for it:

sage: latex(g)

\begin{tikzpicture}
\definecolor{cv0}{rgb}{0.0,0.0,0.0}
\definecolor{cfv0}{rgb}{1.0,1.0,1.0}
\definecolor{clv0}{rgb}{0.0,0.0,0.0}
\definecolor{cv1}{rgb}{0.0,0.0,0.0}
\definecolor{cfv1}{rgb}{1.0,1.0,1.0}
\definecolor{clv1}{rgb}{0.0,0.0,0.0}
\definecolor{cv2}{rgb}{0.0,0.0,0.0}
\definecolor{cfv2}{rgb}{1.0,1.0,1.0}
\definecolor{clv2}{rgb}{0.0,0.0,0.0}
\definecolor{cv0v2}{rgb}{0.0,0.0,0.0}
\definecolor{cv1v0}{rgb}{0.0,0.0,0.0}
\definecolor{cv2v1}{rgb}{0.0,0.0,0.0}
%
\Vertex[style={minimum size=1.0cm,draw=cv0,fill=cfv0,text=clv0,shape=circle},LabelOut=false,L=\hbox{$1$},x=1.6204cm,y=5.0cm]{v0}
\Vertex[style={minimum size=1.0cm,draw=cv1,fill=cfv1,text=clv1,shape=circle},LabelOut=false,L=\hbox{$2$},x=0.0cm,y=0.0cm]{v1}
\Vertex[style={minimum size=1.0cm,draw=cv2,fill=cfv2,text=clv2,shape=circle},LabelOut=false,L=\hbox{$3$},x=5.0cm,y=1.1015cm]{v2}
%
\Edge[lw=0.1cm,style={post, bend right,color=cv0v2,},](v0)(v2)
\Edge[lw=0.1cm,style={post, bend right,color=cv1v0,},](v1)(v0)
\Edge[lw=0.1cm,style={post, bend right,color=cv2v1,},](v2)(v1)
%
\end{tikzpicture}

This might print a couple of warnings about required LaTeX packages.

The urls for them are outdated, see instead

• https://www.ctan.org/pkg/tkz-berge
• https://www.ctan.org/pkg/tkz-graph

Updating those links in the warnings and in the LaTeX tutorial is tracked at

• https://trac.sagemath.org/ticket/30212

Unfortunately, p.show computes the graph internally and just outputs the figure output. Put, we can do it from scratch:

sage: p = Permutation([3,1,2])
sage: edges = list(enumerate(p,start=1))
sage: d = DiGraph(edges, format='list_of_edges', loops=True)
sage: d
Looped digraph on 3 vertices
sage: latex(d) # prints the latexoutput in the default tikz
sage: view(d) # opens the pdf in a viewer

There is another way to use graphviz + dot2tex, but I always forget how to do it. Personnaly, I like to use the TikzPicture class from my package which sets up properly the options to use graphviz + dot2tex to constructs the tikzpicture:

sage: from slabbe import TikzPicture
sage: tikz = TikzPicture.from_graph(d)
sage: print(tikz)
\documentclass[tikz]{standalone}
\standaloneconfig{border=4mm}
\usepackage{amsmath}
\begin{document}
\begin{tikzpicture}[>=latex,line join=bevel,]
%%
\node (node_0) at (23.0bp,104.5bp) [draw,draw=none] {$1$};
  \node (node_2) at (6.0bp,55.5bp) [draw,draw=none] {$3$};
  \node (node_1) at (23.0bp,6.5bp) [draw,draw=none] {$2$};
  \draw [black,->] (node_0) ..controls (18.571bp,91.254bp) and (14.669bp,80.466bp)  .. (node_2);
  \draw [black,->] (node_1) ..controls (23.0bp,27.341bp) and (23.0bp,65.653bp)  .. (node_0);
  \draw [black,->] (node_2) ..controls (10.429bp,42.254bp) and (14.331bp,31.466bp)  .. (node_1);
%
\end{tikzpicture}
\end{document}
sage: tikz.pdf()                        # opens up a viewer
sage: tikz.pdf('filename.pdf')   # saves the pdf file

To install those optional packages, you do:

sage -i dot2tex
sage -pip install slabbe

At some point, I might move the TikzPicture code from my package to sage. Is this something you would like for instance?