A bad instance for k-means++

  • Authors:
  • Tobias Brunsch;Heiko Röglin

  • Affiliations:
  • -;-

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2013

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Abstract

k-means++ is a seeding technique for the k-means method with an expected approximation ratio of O(logk), where k denotes the number of clusters. Examples are known on which the expected approximation ratio of k-means++ is @W(logk), showing that the upper bound is asymptotically tight. However, it remained open whether k-means++ yields a constant approximation with probability 1/poly(k) or even with constant probability. We settle this question and present instances on which k-means++ achieves an approximation ratio no better than (2/3-@e)@?logk with probability exponentially close to 1.