A simplification of the C-realizability criterion for the Nonnegative Inverse Eigenvalue Problem for integers

Abstract

A multiset $\Lambda =\{{\lambda }_1,\dots ,{\lambda }_n\}$ of complex numbers is said to be realizable whenever there exists a nonnegative matrix of order $n$ with spectrum $\Lambda$. One of the broadest criterion that guarantees realizability is the $C-$realizability. It says that $\Lambda$, with real numbers, is $C-$realizable if it can be obtained starting from $n$ basic multisets $\{0\},\dots ,\{0\}$ by successively applying any finite number of times any of the following rules: (a) join two of the multisets; (b) increase by $\epsilon >0$ the Perron root of one of the multisets; (c) increase by $\epsilon >0$ the Perron root of one of the multisets and simultaneously increase or decrease by $\epsilon$ any other value of the same multiset.