Graphs with a small number of nonnegative eigenvalues
Using a mixture of computer search and theoretical consideration, the author determines all graphs with at most two nonnegative eigenvalues. Having noted that \(2K_1\) is the only minimal graph with two nonnegative eigenvalues, the author goes on to determine all minimal graphs with three nonnegative eigenvalues. There are exactly 285 such graphs.
scientific article; zbMATH DE number 1332854