The macro \EdgeDoubleMod is convenient when drawing some complicated graphs. Consider the following picture of the line graph of the Petersen graph.

Line graph of the Petersen graph

produced by: 

\begin{tikzpicture}
  \SetVertexNormal[MinSize=12pt]
  \tikzset{VertexStyle/.append style=
    {inner sep=0pt,font=\footnotesize\sffamily}}
  \begin{scope}[rotate=-90]
    \grCirculant[RA=0.6,prefix=a]{5}{2}
  \end{scope}
  \begin{scope}[rotate=-18]
    \grEmptyCycle[RA=1.5,prefix=b]{5}{2}
  \end{scope}
  \begin{scope}[rotate=18]
    \grCycle[RA=2.5,prefix=c]{5}
  \end{scope}
  \EdgeIdentity{a}{b}{5} 
  \EdgeIdentity{b}{c}{5}
  {\tikzset{EdgeStyle/.append style = {blue,line width=3pt}}
  \EdgeDoubleMod{b}{5}{0}{1}{a}{5}{2}{1}{5}}
  {\tikzset{EdgeStyle/.append style = {green,line width=2pt}}
  \EdgeDoubleMod{c}{5}{0}{1}{b}{5}{1}{1}{5}}
\end{tikzpicture}

We construct the graph using tree cycles: a circulant, an “empty” cycle and a usual cycle. The code \EdgeIdentity{a}{b}{5} just joins, for each i from 0 to 4 (that is, five times) the vertex labeled a_i to the vertex labeled b_i.

Finally \EdgeDoubleMod{b}{5}{0}{1}{a}{5}{2}{1}{5} joins, for each i between 0 and 4 (that is the 5 in the last argument), the vertex labeled b_{0+1\cdot i} to the vertex labeled a_{2+1\cdot i}. In both cases, the sub-index is calculated mod 5 (because of the second and the sixth argument).

See also: Original Source by Rafael

Note: The copyright belongs to the blog author and the blog. For the license, please see the linked original source blog.