Long Dominating Cycles in Graphs

All graphs considered in this paper will be finite and simple. We use Bondy & Murty for terminology and notations not defined here

Long dominating cycles and paths in graphs with large neighborhood unions

Let G be a graph of order n and define NC(G) = min{|N(u)U N(v)| |uv E(G)}. A cycle C of G is called a dominating cycle or D-cycle if V(G) - V(C) is an independent set. A D-path is defined analogously. The following result is proved: if G is 2-connected and contains a D-cycle, then G contains a D-cycle of length at least min{n, 2NC(G)} unless G is the Petersen graph. By combining this result with a known sufficient condition for the existence of a D-cycle, a common generalization of Ore's Theorem and several recent neighborhood union results is obtained. An analogous result on long D-paths is also established

A note on dominating cycles in 2-connected graphs

Let G be a 2-connected graph on n vertices such that d(x) + d(y) + d(z) n for all triples of independent vertices x, y, z. We prove that every longest cycle in G is a dominating cycle unless G is a spanning subgraph of a graph belonging to one of four easily specified classes of graphs