On [plus/minus] 1 eigenvectors of graphsStevanović, Dragan (Avtor) eigenvectoradjacency matrixWilf's problemWhile discussing his spectral bound on the independence number of a graph, Herbert Wilf asked back in 1986 what kind of a graph admits an eigenvector consisting solely of ▫$\pm 1$▫ entries? We prove that Wilf's problem is NP-complete, but also that the set of graphs having a ▫$\pm 1$▫ eigenvector is quite rich, being closed under a number of different graph compositions.20162022-01-03 00:47:11Neznano17622sl