Note: Independence in connected graphs

  • Authors:
  • Jochen Harant;Dieter Rautenbach

  • Affiliations:
  • Institut für Mathematik, TU Ilmenau, Postfach 100565, D-98684 Ilmenau, Germany;Institut für Optimierung und Operations Research, Universität Ulm, D-89069 Ulm, Germany

  • Venue:
  • Discrete Applied Mathematics
  • Year:
  • 2011

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Abstract

We prove that if G=(V"G,E"G) is a finite, simple, and undirected graph with @k components and independence number @a(G), then there exist a positive integer k@?N and a function f:V"G-N"0 with non-negative integer values such that f(u)@?d"G(u) for u@?V"G, @a(G)=k=@?"u"@?"V"""G1d"G(u)+1-f(u), and @?"u"@?"V"""Gf(u)=2(k-@k). This result is a best possible improvement of a result due to Harant and Schiermeyer [J. Harant, I. Schiermeyer, On the independence number of a graph in terms of order and size, Discrete Math. 232 (2001) 131-138] and implies that @a(G)n(G)=2(d(G)+1+2n(G))+(d(G)+1+2n(G))^2-8 for connected graphs G of order n(G), average degree d(G), and independence number @a(G).