Mehler formulae for matching polynomials of graphs and independence polynomials of clawfree graphs

  • Authors:
  • Bodo Lass

  • Affiliations:
  • Université/ de Lyon/ Université/ Lyon 1/ INSA de Lyon, F-69621/ Ecole Centrale de Lyon/ CNRS, UMR5208, Institut Camille Jordan, 43 blvd du 11 novembre 1918, F-69622 Villeurbanne-Cedex, Fra ...

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2012

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Abstract

The independence polynomial of a graph G is the polynomial @?"Ix^|^I^|, summed over all independent subsets I@?V(G). We show that if G is clawfree, then there exists a Mehler formula for its independence polynomial. This was proved for matching polynomials in Lass (2004) [19] and extends the combinatorial proof of the Mehler formula found by Foata (1978) [9]. It implies immediately that all the roots of the independence polynomial of a clawfree graph are real, answering a question posed by Hamidoune (1990) [14] and Stanley (1998) [28] and solved by Chudnovsky and Seymour (2007) [6]. We also prove a Mehler formula for the multivariate matching polynomial, extending results of Lass (2004) [19].