6

I am using the following code to draw a Petersen graph in LaTeX beamer:

\documentclass{article}
\usepackage{tkz-berge}
\begin{document}
\begin{tikzpicture}[rotate=90]
\GraphInit[vstyle=Art]
\grPetersen[RA=5, RB=3]
\end{tikzpicture}
\end{document}

The graph, all vertices with the same colour

It outputs a Petersen graph with all the nodes. I can't find how to color the vertices differently. I figured out how to change the color of all the vertices, but this is not what I need. I need to color one vertex red, then an adjacent one say blue, and so on. How to do this?

Martin Schröder
  • 15,156
Mat
  • 73

1 Answers1

2

Generally, I find tkz-berge is useful for doing standard graphs quickly in a pinch, but if I need to deviate from a standard graph, it's usually faster to break out plain TikZ and write it from scratch. That's what I've done in the example below.

A tkz guru may be able to colour the vertices differently with ease, but I found this method easier (and fairly simple).

Here's what it looks like:

enter image description here

and here's the associated code:

\documentclass{article}
\usepackage{tkz-berge}
\begin{document}

% Draw a cycle of vertices
\newcommand*{\drawvertices}[7]{
  \foreach \t/\mycolor in {1/#1, 2/#2, 3/#3, 4/#4, 5/#5} {
    \begin{scope}[rotate = \t * 72, xshift=#6,
      VertexStyle/.append style = {ball color = \mycolor}]
      \Vertex{#7\t}
    \end{scope}
  }
}

% Inner 5-cycle
\newcommand*{\innervertices}[5]{
  \drawvertices{#1}{#2}{#3}{#4}{#5}{\RA}{a}
}

% Outer 5-cycle
\newcommand*{\outervertices}[5]{
  \drawvertices{#1}{#2}{#3}{#4}{#5}{\RB}{b}
}

% The star-like edges in the inner cycle
\newcommand*{\staredges}[5]{
  \foreach \u/\v/\edgecolor in {1/3/#1, 3/5/#2, 5/2/#3, 2/4/#4, 4/1/#5} {
    \tikzstyle{EdgeStyle} = [color = \edgecolor]
    \Edges(a\u, a\v)
  }
}

% The outermost edges
\newcommand*{\outeredges}[5]{
  \foreach \u/\v/\edgecolor in {1/2/#1, 2/3/#2, 3/4/#3, 4/5/#4, 5/1/#5} {
    \tikzstyle{EdgeStyle} = [color = \edgecolor]
    \Edges(b\u, b\v)
  }
}

% The edges that join the inner and the outer five cycle
\newcommand*{\betweenedges}[5]{
  \foreach \u/\edgecolor in {1/#1, 2/#2, 3/#3, 4/#4, 5/#5} {
    \tikzstyle{EdgeStyle} = [color = \edgecolor]
    \Edges(a\u, b\u)
  }
}

\begin{tikzpicture}[rotate=90]
\GraphInit[vstyle=Art]

% Set the inner and outer radius as with \grPetersen
\newcommand*{\RA}{2.4cm}
\newcommand*{\RB}{5cm}

\innervertices{green}{red}{orange}{yellow}{blue}
\outervertices{purple}{cyan}{magenta}{lime}{pink}

\staredges{red}{orange}{green}{blue}{pink}

\outeredges{green}{blue}{purple}{cyan}{yellow}

\betweenedges{blue}{pink}{cyan}{teal}{yellow}

% Get numbered labels (like in the picture)
% \foreach \number in {1,...,5} {
%  \begin{scope}[rotate = \number * 72, xshift=\RB+0.8cm]
%    \draw (0,0) node {\LARGE{$\number$}};
%  \end{scope}
% }

\end{tikzpicture}
\end{document}

What you change

You need to set \RA and \RB to the inner/outer radii that you want; there are analogous to the parameters RA and RB in \grPetersen.

In each of the commands from \innervertices{} to \betweenedges{}, change the colours for those that you'd like. Each time, you start at the vertex or edge incident with 1, and head counter-clockwise. (Look at the picture if it helps.)

The colors are defined by xcolor. You can find a list of the standard colors on page 17 of the package documentation, or find out how to define your own colours in the same document.

I set up vertices just as you do in tkz-berge normally: with a \Vertex command, and they're moved to the appropriate position with a scope. These are then joined with the tkz-berge command \Edges().

alexwlchan
  • 5,417