This macro is useful for circulants. Observe:

\begin{tikzpicture}
\grCycle[prefix=a,RA=3]{14}
\EdgeInGraphMod{a}{8}{3}
\end{tikzpicture}


which produces:

This means that the edges ai – ai+3 are added to the graph, starting when i=0 and whenever i+3<8. The “3” here is the third argument of the macro, and the “8” is the second. The “a” is the identifier of the vertices joined by the added edges.

Hence the circulant is obtained by:

\begin{tikzpicture}
\grCycle[RA=3]{14}
\EdgeInGraphMod{a}{14}{3}
\end{tikzpicture}


that is: