Non-negative spectrum of a digraph
Digraphs are considered by means of eigenvalues of the matrix AAT, and similarly ATA, where A is the adjacency matrix of a digraph. The common spectrum of these matrices is called non-negative spectrum or N-spectrum of a digraph. Several properties of the N-spectrum are proved. The notion of cospectrality is generalized, and some examples of cospectral (multi)(di)graphs are constructed.
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