Abstract

"Let Λ= {λ1, λ2, . . . , λn} be a set of complex numbers. The nonnegative inverse eigenvalue problem (NIEP) is the problem of determining necessary and su.cient conditions in order that Λmay be the spectrum of an entrywise nonnegative n Χ n matrix. If there exists a nonnegative matrix A with spectrum Λ we say that Λ is realized by A.If the matrix A must be symmetric we have the symmetric nonnegative inverse eigenvalue problem (SNIEP). This paper presents a simple realizability criterion by symmetric nonnegative matrices. The proof is constructive in the sense that one can explicitly construct symmetric nonnegative matrices realizing Λ"