New Constructions of Weak ε-Nets

  • Authors:
  • Jirí Matousek;Uli Wagner

  • Affiliations:
  • Department of Applied Mathematics and Institute for Theoretical Computer Science (ITI), Charles University, Malostranskénám 25, 118 00 Praha 1, Czech Republic;Institut für Theoretische Informatik, ETH Zürich, CH-8092 Zürich, Switzerland

  • Venue:
  • Discrete & Computational Geometry
  • Year:
  • 2004

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Abstract

A finite set $N \subset \R^d$ is a {\em weak $\eps$-net} for an $n$-point set $X\subset \R^d$ (with respect to convex sets) if $N$ intersects every convex set $K$ with $|K\,\cap\,X|\geq \eps n$. We give an alternative, and arguably simpler, proof of the fact, first shown by Chazelle et al., that every point set $X$ in $\R^d$ admits a weak $\eps$-net of cardinality $O(\eps^{-d}\polylog(1/\eps))$. Moreover, for a number of special point sets (e.g., for points on the moment curve), our method gives substantially better bounds. The construction yields an algorithm to construct such weak $\eps$-nets in time $O(n\ln(1/\eps))$.