On k-convex polygons

  • Authors:
  • Oswin Aichholzer;Franz Aurenhammer;Erik D. Demaine;Ferran Hurtado;Pedro Ramos;Jorge Urrutia

  • Affiliations:
  • Institute for Software Technology, University of Technology, Graz, Austria;Institute for Theoretical Computer Science, University of Technology, Graz, Austria;Computer Science and Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, USA;Departament de Matemítica Aplicada II, Universitat Politècnica de Catalunya, Barcelona, Spain;Departamento de Matemáticas, Universidad de Alcalá, Madrid, Spain;Instituto de Matemáticas, Universidad Nacional Autónoma de México, Autónoma de México, Mexico

  • Venue:
  • Computational Geometry: Theory and Applications
  • Year:
  • 2012

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Abstract

We introduce a notion of k-convexity and explore polygons in the plane that have this property. Polygons which are k-convex can be triangulated with fast yet simple algorithms. However, recognizing them in general is a 3SUM-hard problem. We give a characterization of 2-convex polygons, a particularly interesting class, and show how to recognize them in O(nlogn) time. A description of their shape is given as well, which leads to Erdos-Szekeres type results regarding subconfigurations of their vertex sets. Finally, we introduce the concept of generalized geometric permutations, and show that their number can be exponential in the number of 2-convex objects considered.