Recursive construction for 3-regular expanders

  • Authors:
  • M. Ajtai

  • Affiliations:
  • -

  • Venue:
  • SFCS '87 Proceedings of the 28th Annual Symposium on Foundations of Computer Science
  • Year:
  • 1987

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Abstract

We present an algorithm which in n3(log n)3 time constructs a 3- regular expander graph on n vertices. In each step we substitute a pair of edges of the graph by a new pair of edges so that the total number of cycles of length s = [c log n] decreases (for some fixed absolute constant c). When we reach a local minimum in the number of cycles of length s the graph is an expander. The proof is completely elementary, we use only the basic results about the eigenvalues and eigenvectors of symmetric matrices.