Sufficient conditions for graphs to be λ′-optimal, super-edge-connected, and maximally edge-connected

  • Authors:
  • Angelika Hellwig;Lutz Volkmann

  • Affiliations:
  • Lehrstuhl II Für Mathematik, RWTH Aachen University, 52056 Aachen, Germany;Lehrstuhl II Für Mathematik, RWTH Aachen University, 52056 Aachen, Germany

  • Venue:
  • Journal of Graph Theory
  • Year:
  • 2005

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Abstract

The restricted-edge-connectivity of a graph G, denoted by λ′(G), is defined as the minimum cardinality over all edge-cuts S of G, where G-S contains no isolated vertices. The graph G is called λ′-optimal, if λ′(G) = ξ(G), where ξ(G) is the minimum edge-degree in G. A graph is super-edge-connected, if every minimum edge-cut consists of edges adjacent to a vertex of minimum degree. In this paper, we present sufficient conditions for arbitrary, triangle-free, and bipartite graphs to be λ′-optimal, as well as conditions depending on the clique number. These conditions imply super-edge-connectivity, if δ (G) ≥ 3, and the equality of edge-connectivity and minimum degree. Different examples will show that these conditions are best possible and independent of other results in this area. © 2005 Wiley Periodicals, Inc. J Graph Theory 48: 228–246, 2005