3 research outputs found
Laplacian Distribution and Domination
Let denote the number of Laplacian eigenvalues of a graph in an
interval , and let denote its domination number. We extend the
recent result , and show that isolate-free graphs also
satisfy . In pursuit of better understanding Laplacian
eigenvalue distribution, we find applications for these inequalities. We relate
these spectral parameters with the approximability of , showing that
. However, for -cyclic graphs, . For trees ,
Laplacian eigenvalue distribution, diameter and domination number of trees
For a graph with domination number , Hedetniemi, Jacobs and
Trevisan [European Journal of Combinatorics 53 (2016) 66-71] proved that
, where means the number of Laplacian
eigenvalues of in the interval . Let be a tree with diameter
. In this paper, we show that . However, such a
lower bound is false for general graphs. All trees achieving the lower bound
are completely characterized. Moreover, for a tree , we establish a relation
between the Laplacian eigenvalues, the diameter and the domination number by
showing that the domination number of is equal to if and only if
it has exactly Laplacian eigenvalues less than one. As an
application, it also provides a new type of trees, which show the sharpness of
an inequality due to Hedetniemi, Jacobs and Trevisan
Proof of a conjecture on distribution of Laplacian eigenvalues and diameter, and beyond
Ahanjideh, Akbari, Fakharan and Trevisan proposed a conjecture in [Linear
Algebra Appl. 632 (2022) 1--14] on the distribution of the Laplacian
eigenvalues of graphs: for any connected graph of order with diameter that is not a path, the number of Laplacian eigenvalues in the interval
is at most . We show that the conjecture is true, and give a
complete characterization of graphs for which the conjectured bound is
attained. This establishes an interesting relation between the spectral and
classical parameters