A characterization of trace zero bisymmetric nonnegative $5 \times 5$ matrices

Abstract

Let $\lambda_1 \geq \lambda_2 \geq \lambda_3 \geq \lambda_4 \geq \lambda_5 \geq -\lambda_1$ be real numbers such that $\sum_{i=1}^5 \lambda_i =0$. In \cite{oren}, O. Spector prove that a necessary and sufficient condition for $\lambda_1, \lambda_2, \lambda_3, \lambda_4, \lambda_5$ to be the eigenvalues of a symmetric nonnegative $5 \times 5$ matrix is "$\lambda_2+\lambda_5<0$ and $\sum_{i=1}^5 \lambda_{i}^{3} \geq 0"$. In this article, we show that this condition is also a necessary and sufficient condition for $\lambda_1, \lambda_2, \lambda_3, \lambda_4, \lambda_5$ to be the spectrum of a traceless bisymmetric nonnegative $5 \times 5$ matrix.