2

Is there a fast way to add a central vertex connected to all others after drawing the cycle graph using the graph library of the tikz package?

This is what the code currently looks like:

\documentclass{article}
\begin{document}                                             
\usepackage{tikz}
\usetikzlibrary{graphs,graphs.standard}

\begin{tikzpicture}[scale=0.8,every node/.style={scale=0.8}]
    \graph  [nodes={circle,fill=black!25}, edges={black!60, semithick}, clockwise, radius=8em,
    n=9, p=0.3] 
        { subgraph C_n [n=6,m=3,clockwise,radius=2cm] };
\end{tikzpicture}
\end{document}
1
  • 2
    Please make your code compilable by adding documentclass, \begin{document}, ... – hpekristiansen Sep 17 '20 at 23:11
7

Give a name to subgraph and then you can use the vertices. Finally find the center of subgraph and draw from center to each vertices.

\documentclass[tikz,margin=3mm]{standalone}

\usetikzlibrary{graphs,graphs.standard,calc}
\begin{document}
\begin{tikzpicture}[scale=0.8,every node/.style={scale=0.8}]
    \graph  [nodes={circle,fill=black!25}, edges={black!60, semithick}, clockwise, radius=8em,
    n=9, p=0.3] 
        { subgraph C_n [n=6,m=3,clockwise,radius=2cm,name=A] };
        \node at  ($(A 1)!.5!(A 4)$) (C){};
        \foreach \i in {1,2,...,6}{
        \draw (C)-- (A \i); }
        \draw [fill=black!25](C) circle (0.4em);
\end{tikzpicture}
\end{document}

enter image description here

ADDENDUM: According to pgf manual on page 212, you can use mid definition.

\documentclass[tikz,margin=3mm]{standalone}

\usetikzlibrary{graphs,graphs.standard,calc}
\begin{document}
\begin{tikzpicture}[scale=0.8,every node/.style={scale=0.8}]
    \graph  [empty nodes, nodes={circle,fill=black!25}, edges={black!60, semithick}, clockwise, radius=8em,
    n=9, p=0.3] 
        { subgraph C_n [n=6,m=3,clockwise,radius=2cm,name=A]-- mid};
        \node at  ($(A 1)!.5!(A 4)$) (C){1};
        \foreach \i [count=\xi from 2]  in {1,2,...,6}{
        \node at (A \i){\xi}; }
\end{tikzpicture}
\end{document}

enter image description here

4
  • Thank you. If I wanted the central vertex to look the same as all others, and number it as 1 (so that current number 1 becomes 2, etc...), how should I modify your code? I set its size to 0.8em and added the tag 1, but I'm note sure how to remove the boundary and change the other numbers... – BigDinosaur Sep 18 '20 at 11:25
  • 1
    I like very much your work. – Sebastiano Sep 18 '20 at 11:38
  • 1
    @BigDinosaur, your welcome. I have edited my answer. – user31034 Sep 18 '20 at 12:16
  • 1
    @Sebastiano, thank you very much. – user31034 Sep 18 '20 at 12:17

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