The algorithmic aspects of the regularity lemma

  • Authors:
  • N. Alon

  • Affiliations:
  • Dept. of Math., Raymond&Beverly Sackler Faculty of Exact Sciences, Tel Aviv Univ., Israel

  • Venue:
  • SFCS '92 Proceedings of the 33rd Annual Symposium on Foundations of Computer Science
  • Year:
  • 1992

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Abstract

The regularity lemma of Szemeredi (1978) is a result that asserts that every graph can be partitioned in a certain regular way. This result has numerous applications, but its known proof is not algorithmic. The authors first demonstrate the computational difficulty of finding a regular partition; they show that deciding if a given partition of an input graph satisfies the properties guaranteed by the lemma is co-NP-complete. However, they also prove that despite this difficulty the lemma can be made constructive; they show how to obtain, for any input graph, a partition with the properties guaranteed by the lemma, efficiently. The desired partition, for an n-vertex graph, can be found in time O(M(n)), where M(n)=O(n/sup 2.376/) is the time needed to multiply two n by n matrices with 0,1-entries over the integers. The algorithm can be parallelized and implemented in NC/sup 1/.