How Fast Is the k-Means Method?

  • Authors:
  • Sariel Har-Peled;Bardia Sadri

  • Affiliations:
  • Department of Computer Science, University of Illinois, 201 N. Goodwin Avenue, Urbana, IL 61801, USA;Department of Computer Science, University of Illinois, 201 N. Goodwin Avenue, Urbana, IL 61801, USA

  • Venue:
  • Algorithmica
  • Year:
  • 2005

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Abstract

We present polynomial upper and lower bounds on the number of iterations performed by the k-means method (a.k.a. Lloyd’s method) for k-means clustering. Our upper bounds are polynomial in the number of points, number of clusters, and the spread of the point set. We also present a lower bound, showing that in the worst case the k-means heuristic needs to perform Ω(n) iterations, for n points on the real line and two centers. Surprisingly, the spread of the point set in this construction is polynomial. This is the first construction showing that the k-means heuristic requires more than a polylogarithmic number of iterations. Furthermore, we present two alternative algorithms, with guaranteed performance, which are simple variants of the k-means method. Results of our experimental studies on these algorithms are also presented.