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New theorems for signless Laplacian eigenvalues. (English) Zbl 1199.05212
The author extends his previous surveys of properties of $$Q$$-spectrum (i.e., the spectrum of a graph based on its signless Laplacian matrix). Some new contributions are included. In particular, graphs whose largest eigenvalue (with respect to signless Laplacian) does not exceed $$4$$ are characterized. The $$Q$$-spectra of all connected graphs on six vertices are given in Appendix.

##### MSC:
 05C50 Graphs and linear algebra (matrices, eigenvalues, etc.)
##### Keywords:
graph spectrum; subdivision graph; tree; unicyclic graph
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