On the dependence polynomial of a graph

  • Authors:
  • Jianguo Qian;Andreas Dress;Yan Wang

  • Affiliations:
  • Department of Mathematics, Xiamen University, Xiamen, Fujian, PR China and Department of Mathematics, University of Bielefeld, Bielefeld, Germany;Department of Mathematics, University of Bielefeld, Bielefeld, Germany and Max Planck Institute for Mathematics in the Sciences, Leipzig, Germany;Department of Mathematics, Xiamen University, Xiamen, Fujian, PR China

  • Venue:
  • European Journal of Combinatorics
  • Year:
  • 2007

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Abstract

The dependence polynomial PG = PG(z) of a graph G is defined by PG(z) := Σi=0n (-1)icizi where ci = ci(G) is the number of complete subgraphs of G of cardinality i. It is clear that the complete subgraphs of G form a poset relative to subset inclusion. Using Möbius inversion, this yields various identities involving dependence polynomials implying in particular that the dependence polynomial of the line graph L(G) of G is determined uniquely by the (multiset of) vertex degrees of G and the number of triangles in G. Furthermore, the dependence polynomial of the complement of the line graph of G is closely related to the matching polynomial of G, one of the most 'prominent' polynomials studied in graph theory.