Oliveira, Carla Silva, de Lima, Leonardo Silva, de Abreu, Nair Maria Maia and Kirkland, Steve (2010) Bounds on the Q-spread of a graph. Linear Algebra and its Applications, 432 (9). pp. 2342-2351. ISSN 0024-3795
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Abstract
The spread s(M) of an n × n complex matrix M is s(M) = maxij |_i − _j |, where
the maximum is taken over all pairs of eigenvalues of M, _i, 1 ≤ i ≤ n, [9] and
[11]. Based on this concept, Gregory et al. [7] determined some bounds for the
spread of the adjacency matrix A(G) of a simple graph G and made a conjecture
regarding the graph on n vertices yielding the maximum value of the spread of
the corresponding adjacency matrix. The signless Laplacian matrix of a graph G,
Q(G) = D(G)+A(G), where D(G) is the diagonal matrix of degrees of G and A(G)
is its adjacency matrix, has been recently studied, [4], [5]. The main goal of this
paper is to determine some bounds on s(Q(G)). We prove that, for any graph on
n ≥ 5 vertices, 2 ≤ s(Q(G)) ≤ 2n − 4, and we characterize the equality cases in
both bounds. Further, we prove that for any connected graph G with n ≥ 5 vertices,
s(Q(G)) < 2n − 4. We conjecture that, for n ≥ 5, sQ(G) ≤ √4n2 − 20n + 33 and
that, in this case, the upper bound is attained if, and only if, G is a certain path-
complete graph.
  
  | Item Type: | Article | 
|---|---|
| Additional Information: | Preprint submitted to Elsevier | 
| Keywords: | spectrum; signless Laplacian matrix; spread; path complete graph; | 
| Academic Unit: | Faculty of Science and Engineering > Research Institutes > Hamilton Institute | 
| Item ID: | 2187 | 
| Depositing User: | Professor Steve Kirkland | 
| Date Deposited: | 13 Oct 2010 15:34 | 
| Journal or Publication Title: | Linear Algebra and its Applications | 
| Publisher: | Elsevier | 
| Refereed: | No | 
| Related URLs: | |
| Use Licence: | This item is available under a Creative Commons Attribution Non Commercial Share Alike Licence (CC BY-NC-SA). Details of this licence are available here | 
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