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A connected graph is called Q-controllable if its signless Laplacian eigenvalues are mutually distinct and main. Two graphs G and H are said to be Q-cospectral if they share the same signless Laplacian spectrum. In this paper, infinite families of Q-controllable graphs are constructed, by using the operator of rooted product introduced by Godsil and McKay. In the process, infinitely many non-is...

In this paper, we present a sharp upper and lower bounds for the signless Laplacian spectral radius of graphs in terms of clique number. Moreover, the extremal graphs which attain the upper and lower bounds are characterized. In addition, these results disprove the two conjectures on the signless Laplacian spectral radius in [P. Hansen and C. Lucas, Bounds and conjectures for the signless Lapla...

For a connected graph G on n vertices, recall that the reciprocal distance signless Laplacian matrix of is defined to be RQ(G)=RT(G)+RD(G), where RD(G) matrix, RT(G)=diag(RT1,RT2,⋯,RTn) and RTi degree vertex vi. In 2022, generalized which by RDα(G)=αRT(G)+(1−α)RD(G),α∈[0,1], was introduced. this paper, we give some bounds spectral radius RDα(G) characterize its extremal graph. addition, also li...

The signless Laplacian Q and edge-Laplacian S of a given graph may or not be invertible. Moore-Penrose inverses are studied. In particular, using the incidence matrix, we find combinatorial formulas for trees. Also, present odd unicyclic graphs.

Parallel to the signless Laplacian spectral theory, we introduce and develop the nonlinear spectral theory of signless 1-Laplacian on graphs. Again, the first eigenvalue μ1 of the signless 1-Laplacian precisely characterizes the bipartiteness of a graph and naturally connects to the maxcut problem. However, the dual Cheeger constant h+, which has only some upper and lower bounds in the Laplacia...

For n ≥ 11, we determine all the unicyclic graphs on n vertices whose signless Laplacian spectral radius is at least n− 2. There are exactly sixteen such graphs and they are ordered according to their signless Laplacian spectral radii.