An extended tree-width notion for directed graphs related to the computation of permanents

  • Authors:
  • Klaus Meer

  • Affiliations:
  • Lehrstuhl Theoretische Informatik, BTU Cottbus, Cottbus, Germany

  • Venue:
  • CSR'11 Proceedings of the 6th international conference on Computer science: theory and applications
  • Year:
  • 2011

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Abstract

It is well known that permanents of matrices of bounded treewidth are efficiently computable. Here, the tree-width of a square matrix M = (mij) with entries from a field K is the tree-width of the underlying graph GM having an edge (i, j) if and only if the entry mij ≠ 0. Though GM is directed this does not influence the tree-width definition. Thus, it does not reflect the lacking symmetry when mij ≠ 0 but mji = 0. The latter however might have impact on the computation of the permanent. In this paper we introduce and study an extended notion of tree-width called triangular tree-width. We give examples where the latter parameter is bounded whereas the former is not. As main result we show that permanents of matrices of bounded triangular tree-width are efficiently computable. This result holds as well for the Hamiltonian Cycle problem.