Limit points of eigenvalues of (di)graphs
The study on limit points of eigenvalues of undirected graphs was initiated by A. J. Hoffman in 1972. Now we extend the study to digraphs. We prove: 1. Every real number is a limit point of eigenvalues of graphs. Every complex number is a limit point of eigenvalues of digraphs. 2. For a digraph , the set of limit points of eigenvalues of iterated subdivision digraphs of is the unit circle in the complex plane if and only if has a directed cycle. 3. Every limit point of eigenvalues of a set...