Characteristic and Ehrhart Polynomials

  • Authors:
  • Andreas Blass;Bruce E. Sagan

  • Affiliations:
  • Department of Mathematics, University of Michigan, Ann Arbor, MI 48109-1003. E-mail: ablass@umich.edu;Department of Mathematics, Michigan State University, East Lansing, MI 48824-1027. E-mail: sagan@math.msu.edu

  • Venue:
  • Journal of Algebraic Combinatorics: An International Journal
  • Year:
  • 1998

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Abstract

Let A be a subspace arrangement and let χ(A,t) be thecharacteristic polynomial of its intersection lattice L( A). We show thatif the subspaces in A are taken from L(B_n), whereB_n is the type B Weyl arrangement, then χ(A,t) counts acertain set of lattice points. One can use this result to study the partialfactorization of χ(A,t) over the integers and the coefficients of itsexpansion in various bases for the polynomial ring R[t]. Next we prove thatthe characteristic polynomial of any Weyl hyperplane arrangement can beexpressed in terms of an Ehrhart quasi-polynomial for its affine Weylchamber. Note that our first result deals with all subspace arrangementsembedded in B_n while the second deals with all finite Weylgroups but only their hyperplane arrangements.