Convex Polygons in Cartesian Products

Authors Jean-Lou De Carufel, Adrian Dumitrescu, Wouter Meulemans, Tim Ophelders, Claire Pennarun, Csaba D. Tóth, Sander Verdonschot



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Author Details

Jean-Lou De Carufel
  • School of Electrical Engineering and Computer Science, University of Ottawa, Canada
Adrian Dumitrescu
  • Department of Computer Science, University of Wisconsin-Milwaukee, USA
Wouter Meulemans
  • Department of Mathematics and Computer Science, TU Eindhoven, The Netherlands
Tim Ophelders
  • Department of Computational Mathematics, Science and Engineering, Michigan State University, East Lansing, MI, USA
Claire Pennarun
  • LIRMM, CNRS & Université de Montpellier, France
Csaba D. Tóth
  • Department of Mathematics, California State University Northridge, Los Angeles, CA, USA
  • Department of Computer Science, Tufts University, Medford, MA, USA
Sander Verdonschot
  • School of Computer Science, Carleton University, Ottawa, ON, Canada

Acknowledgements

This work was initiated at the 2017 Fields Workshop on Discrete and Computational Geometry (Carleton University, Ottawa, ON, July 31 - August 4, 2017).

Cite AsGet BibTex

Jean-Lou De Carufel, Adrian Dumitrescu, Wouter Meulemans, Tim Ophelders, Claire Pennarun, Csaba D. Tóth, and Sander Verdonschot. Convex Polygons in Cartesian Products. In 35th International Symposium on Computational Geometry (SoCG 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 129, pp. 22:1-22:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)
https://doi.org/10.4230/LIPIcs.SoCG.2019.22

Abstract

We study several problems concerning convex polygons whose vertices lie in a Cartesian product of two sets of n real numbers (for short, grid). First, we prove that every such grid contains a convex polygon with Omega(log n) vertices and that this bound is tight up to a constant factor. We generalize this result to d dimensions (for a fixed d in N), and obtain a tight lower bound of Omega(log^{d-1}n) for the maximum number of points in convex position in a d-dimensional grid. Second, we present polynomial-time algorithms for computing the longest convex polygonal chain in a grid that contains no two points with the same x- or y-coordinate. We show that the maximum size of such a convex polygon can be efficiently approximated up to a factor of 2. Finally, we present exponential bounds on the maximum number of convex polygons in these grids, and for some restricted variants. These bounds are tight up to polynomial factors.

Subject Classification

ACM Subject Classification
  • Theory of computation → Computational geometry
Keywords
  • Erdős-Szekeres theorem
  • Cartesian product
  • convexity
  • polyhedron
  • recursive construction
  • approximation algorithm

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