On the Complexity of Convex Hulls of Subsets of the Two-Dimensional Plane

  • Authors:
  • Ker-I Ko;Fuxiang Yu

  • Affiliations:
  • Department of Computer Science, Stony Brook University, Stony Brook, NY 11794, USA;Department of Computer Science, Stony Brook University, Stony Brook, NY 11794, USA

  • Venue:
  • Electronic Notes in Theoretical Computer Science (ENTCS)
  • Year:
  • 2008

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Abstract

We investigate the computational complexity of computing the convex hull of a two-dimensional set. We study this problem in the polynomial-time complexity theory of real functions based on the oracle Turing machine model. We show that the convex hull of a two-dimensional Jordan domain S is not necessarily recursively recognizable even if S is polynomial-time recognizable. On the other hand, if the boundary of a Jordan domain S is polynomial-time computable, then the convex hull of S must be NP-recognizable, and it is not necessarily polynomial-time recognizable if PNP. We also show that the area of the convex hull of a Jordan domain S with a polynomial-time computable boundary can be computed in polynomial time relative to an oracle function in #P. On the other hand, whether the area itself is a #P real number depends on the open question of whether NP=UP.