The non-negative spectrum of a digraph.

Given the adjacency matrix A of a digraph, the eigenvalues of the matrix AA^T constitute the so-called non-negative spectrum of this digraph. We investigate the relation between the structure of digraphs and their non-negative spectra and associated eigenvectors. In particular, it turns out that the non-negative spectrum of a digraph can be derived from the traditional (adjacency) spectrum of certain undirected bipartite graphs. [ABSTRACT FROM AUTHOR]