A spectral lower bound for the treewidth of a graph and its consequences

  • Authors:
  • L. Sunil Chandran;C. R. Subramanian

  • Affiliations:
  • Max-Planck Institute for Informatik, Stuhlsatzenhausweg 85, 66123 Saarbrücken, Germany;The Institute of Mathematical Sciences, Chennai, 600113, India

  • Venue:
  • Information Processing Letters
  • Year:
  • 2003

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Abstract

We give a lower bound for the treewidth of a graph in terms of the second smallest eigenvalue of its Laplacian matrix. We use this lower bound to show that the treewidth of a d-dimensional hypercube is at least ⌊3ċ2d/(2(d + 4))⌋ - 1. The currently known upper bound is O(2d/√d). We generalize this result to Hamming graphs. We also observe that every graph G on n vertices, with maximum degree Δ (1) contains an induced cycle (chordless cycle) of length at least 1 + logΔ (µn/8) (provided G is not acyclic), (2) has a clique minor Kh for some h = Ω((nµ2/(Δ + 2µ)2)1/3), where µ is the second smallest eigenvalue of the Laplacian matrix of G.