Extremal problems on triangle areas in two and three dimensions

JOURNAL OF COMBINATORIAL THEORY SERIES A

卷:116

Article

Dumitrescu, Adrian¹  Sharir, Micha^2,3  Toth, Csaba D.⁴ 

[1] Univ Wisconsin, Dept Comp Sci, Milwaukee, WI 53201 USA

[2] Tel Aviv Univ, Sch Comp Sci, IL-69978 Tel Aviv, Israel

[3] NYU, Courant Inst, New York, NY USA

[4] Univ Calgary, Dept Math, Calgary, AB T2N 1N4, Canada

关键词: Geometric incidences;    Extremal combinatorics;    Crossing number;    Unit-area triangles;    Distinct triangle areas;    Minimum-area triangles;    Maximum-area triangles;    Incidences between points and curves;    Incidences between points and cylinders;   

DOI  :  10.1016/j.jcta.2009.03.008

来源: Elsevier

【 摘 要 】

The study of extremal problems on triangle areas was initiated in a series of papers by Erdos and Purdy in the early 1970s. In this paper we present new results on such problems, concerning the number of triangles of the same area that are spanned by finite point sets in the plane and in 3-space, and the number of distinct areas determined by the triangles. In the plane, our main result is an O(n(44/19)) = O(n(2.3158)) upper bound on the number of unit-area triangles spanned by n points, which is the first breakthrough improving the classical bound of O(n(7/3)) from 1992. We also make progress in a number of important special cases. We show that: (i) For points in convex position, there exist n-element point sets that span Omega(n log n) triangles of unit area. (ii) The number of triangles of minimum (nonzero) area determined by n points is at most 2/3(n(2) - n): there exist n-element point sets (for arbitrarily large n) that span (6/pi(2) - o(1))n(2) minimum-area triangles. (iii) The number of acute triangles of minimum area determined by n points is 0(n); this is asymptotically tight. (iv) For n points in convex position, the number of triangles of minimum area is 0(n); this is asymptotically tight. (v) If no three points are allowed to be collinear. there are n-element point sets that span Omega(n log n)

【 授权许可】

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