Convex Hulls of Point-Sets and Non-uniform Hypergraphs

  • Authors:
  • Hanno Lefmann

  • Affiliations:
  • Fakultät für Informatik, TU Chemnitz, D-09107 Chemnitz, Germany

  • Venue:
  • AAIM '07 Proceedings of the 3rd international conference on Algorithmic Aspects in Information and Management
  • Year:
  • 2007

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Abstract

For fixed integers k茂戮驴 3 and hypergraphs ${\mathcal G}$ on Nvertices, which contain edges of cardinalities at most k, and are uncrowded, i.e., do not contain cycles of lengths 2,3, or 4, and with average degree for the i-element edges bounded by O(Ti茂戮驴 1·(ln T)(k茂戮驴 i)/(k茂戮驴 1)), i= 3, ..., k, for some number T茂戮驴 1, we show that the independence number $\alpha ({\mathcal G})$ satisfies $\alpha ({\mathcal G}) = \Omega ((N/T) \cdot (\ln T)^{1/(k-1)})$. Moreover, an independent set Iof size |I| = 茂戮驴((N/T) ·(ln T)1/(k茂戮驴 1)) can be found deterministically in polynomial time. This extends a result of Ajtai, Komlós, Pintz, Spencer and Szemerédi for uncrwoded uniform hypergraphs. We apply this result to a variant of Heilbronn's problem on the minimum area of the convex hull of small sets of points among npoints in the unit square [0,1]2.