Independent set of intersection graphs of convex objects in 2D

  • Authors:
  • Pankaj K. Agarwal;Nabil H. Mustafa

  • Affiliations:
  • Department of Computer Science, Duke University, Durham, NC;Department of Computer Science, Duke University, Durham, NC

  • Venue:
  • Computational Geometry: Theory and Applications
  • Year:
  • 2006

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Abstract

The intersection graph of a set of geometric objects is defined as a graph G = (S, E) in which there is an edge between two nodes si, sj ∈ S if si ∩ sj ≠ 0. The problem of computing a maximum independent set in the intersection graph of a set of objects is known to be NP-complete for most cases in two and higher dimensions. We present approximation algorithms for computing a maximum independent set of intersection graphs of convex objects in R2. Specifically, given (i) a set of n line segments in the plane with maximum independent set of size α, we present algorithms that find an independent set of size at least (α/(2 log(2n/α)))1/2 in time O(n3) and (α/(2log(2n/α)))1/4 in time O(n4/3 logcn), (ii) a set of n convex objects with maximum independent set of size α, we present an algorithm that finds an independent set of size at least (α/(2log(2n/α)))1/3 in time O(n3 + τ (S)), assuming that S can be preprocessed in time τ(S) to answer certain primitive operations on these convex sets, and (iii) a set of n rectangles with maximum independent set of size βn, for β≤ 1, we present an algorithm that computes an independent set of size Ω (β2n). All our algorithms use the notion of partial orders that exploit the geometric structure of the convex objects.