On the boundary of the set of real spectra of nonnegative matrices Original Research Article

The real nonegative eigenvalue problem is concerned with determining which n-tuples of real numbers are the spectrum of some n-by-n nonnegative matrix. Some questions are presented whose answer could help to characterize the boundary of this set, i.e., the set of those spectra of nonnegative matrices which are not the spectrum of any positive matrix.