On tree-partition-width

  • Authors:
  • David R. Wood

  • Affiliations:
  • Department of Mathematics and Statistics, The University of Melbourne, Melbourne, Australia

  • Venue:
  • European Journal of Combinatorics
  • Year:
  • 2009

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Abstract

A tree-partition of a graph G is a proper partition of its vertex set into 'bags', such that identifying the vertices in each bag produces a forest. The width of a tree-partition is the maximum number of vertices in a bag. The tree-partition-width of G is the minimum width of a tree-partition of G. An anonymous referee of the paper [Guoli Ding, Bogdan Oporowski, Some results on tree decomposition of graphs, J. Graph Theory 20 (4) (1995) 481-499] proved that every graph with tree-width k=3 and maximum degree @D=1 has tree-partition-width at most 24k@D. We prove that this bound is within a constant factor of optimal. In particular, for all k=3 and for all sufficiently large @D, we construct a graph with tree-width k, maximum degree @D, and tree-partition-width at least (18-@e)k@D. Moreover, we slightly improve the upper bound to 52(k+1)(72@D-1) without the restriction that k=3.