Spectrally degenerate graphs: Hereditary case

  • Authors:
  • Zdenk DvořáK;Bojan Mohar

  • Affiliations:
  • Institute for Theoretical Computer Science (ITI),44Institute for Theoretical Computer Science is supported as project 1M0545 by the Ministry of Education of the Czech Republic. Charles University, ...;Department of Mathematics, Simon Fraser University, Burnaby, BC V5A 1S6, Canada

  • Venue:
  • Journal of Combinatorial Theory Series B
  • Year:
  • 2012

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Abstract

It is well known that the spectral radius of a tree whose maximum degree is @D cannot exceed 2@D-1. A similar upper bound holds for arbitrary planar graphs, whose spectral radius cannot exceed 8@D+10, and more generally, for all d-degenerate graphs, where the corresponding upper bound is 4d@D. Following this, we say that a graph G is spectrally d-degenerate if every subgraph H of G has spectral radius at most d@D(H). In this paper we derive a rough converse of the above-mentioned results by proving that each spectrally d-degenerate graph G contains a vertex whose degree is at most 4dlog"2(@D(G)/d) (if @D(G)=2d). It is shown that the dependence on @D in this upper bound cannot be eliminated, as long as the dependence on d is subexponential. It is also proved that the problem of deciding if a graph is spectrally d-degenerate is co-NP-complete.