A new technique for the characterization of graphs with a maximum number of spanning trees

  • Authors:
  • L. Petingi;J. Rodriguez

  • Affiliations:
  • Computer Science Department, 1N-211, College of Staten Island, City University of New York, 2800 Victory Blvd, Staten Island, NY;Computer Science Department, LLC 206, Long Island University, 1 University Plaza, Brooklyn, NY

  • Venue:
  • Discrete Mathematics - Algebraic and topological methods in graph theory
  • Year:
  • 2002

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Abstract

Let Γ(n,e) denote the class of all simple graphs on n nodes and e edges. The number of spanning trees of a graph G is denoted by t(G). A graph G0 ∈ Γ(n,e) is said to be t-optimal if t(G0) ≥ t(G) for all G ∈ Γ(n,e). The problem of characterizing t-optimal graphs for arbitrary n and e is still open, although characterizations of t-optimal graphs for specific pairs (n,e) are known. We introduce a new technique for the characterization of t-optimal graphs, based on an upper bound for the number of spanning trees of a graph G in terms of the degree sequence and the number of induced paths of length two of the complement of G. The technique yields the following new results: (1) Complete, almost-regular multipartite graphs are t-optimal. (2) A complete characterization of t-optimal graphs in Γ(n,e) for n(n - 1)/2 - 3n/2 ≤ e ≤ n(n - 1)/2- n is obtained for n ≥ n0, where n0 can be explicitly determined.