Dehn-Sommerville relations, upper bound theorem, and levels in arrangements

  • Authors:
  • Ketan Mulmuley

  • Affiliations:
  • -

  • Venue:
  • SCG '93 Proceedings of the ninth annual symposium on Computational geometry
  • Year:
  • 1993

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Abstract

In this note, we generalize theh-vector for simple, bounded convexpolytopes [14] to the h-matrix forsimple, bounded k-complexes. Weobserve that the h-matrix isinvariant with respect to the defining linear function, and that theDehn-Sommerville relations and McMullen's Upper Bound Theorem [13] forconvex polytopes follow from the invariance ofthe 0-th row and column ofthis matrix. The invariance of the other entries in theh-matrix should, perhaps, beinvestigated more. One new consequence is that, given any non-degeneratelinear function z, the number oflocal z-minima on thelth level of anyd-dimensional arrangement is boundedby l+d-1d-1, with exact equality if thel-th level is bounded andsimple.