Better expansion for Ramanujan graphs

  • Authors:
  • Nabil Kahale

  • Affiliations:
  • -

  • Venue:
  • SFCS '91 Proceedings of the 32nd annual symposium on Foundations of computer science
  • Year:
  • 1991

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Abstract

The expansion properties of regular graphs are investigated. The best previously known expansion of subsets of linear size of explicit k-regular graphs is k/4. This bound is achieved by nonbipartite Ramanujan graphs of degree k=p+1, which have the property that all but the largest eigenvalue have absolute value at most 2 square root p. The expansion coefficient for linear subsets for nonbipartite Ramanujan graphs is improved to 3(k-2)/8. Other results are established, including improved results about random walks on expanders.