Distinct Triangle Areas in a Planar Point Set

  • Authors:
  • Adrian Dumitrescu;Csaba D. Tóth

  • Affiliations:
  • Deptartment of Computer Science, University of Wisconsin-Milwaukee, WI 53201-0784, USA;Department of Mathematics, MIT, Cambridge, MA 02139, USA

  • Venue:
  • IPCO '07 Proceedings of the 12th international conference on Integer Programming and Combinatorial Optimization
  • Year:
  • 2007

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Abstract

Erdős, Purdy, and Straus conjectured that the number of distinct (nonzero) areas of the triangles determined by nnoncollinear points in the plane is at least $\lfloor \frac{n-1}{2} \rfloor$, which is attained for 茂戮驴n/ 2茂戮驴 and respectively $\lfloor n/2\rfloor$ equally spaced points lying on two parallel lines. We show that this number is at least $\frac{17}{38}n -O(1) \approx 0.4473n$. The best previous bound, $(\sqrt{2}-1)n-O(1)\approx 0.4142n$, which dates back to 1982, follows from the combination of a result of Burton and Purdy [5] and Ungar's theorem [23] on the number of distinct directions determined by nnoncollinear points in the plane.