The L(2,1)-labelling problem for cubic Cayley graphs on dihedral groups
A k-L(2,1)-labelling of a graph G is a mapping f:V(G)?{0,1,2,,k} such that |f(u)?f(v)|?2 if uv?E(G) and f(u)?f(v) if u,v are distance two apart. The smallest positive integer k such that G admits a k-L(2,1)-labelling is called the ?-number ofG. In this paper we study this quantity for cubic Cayley graphs (other than the prism graphs) on dihedral groups, which are called brick product graphs or honeycomb toroidal graphs. We prove that the ?-number of such a graph is between5 and7, and moreover we give a characterisation of such graphs with ?-number5.
cayley graph dihedral group ?-number brick product honeycomb toroidal graph l(2 1)-labelling honeycomb torus