arXiv subjects
Publications and source records attributed to Somchai Somphotphisut.
We give sufficient conditions of the nonnegative inverse eigenvalue problem (NIEP) for normal centrosymmetric matrices. These sufficient conditions are analogous to the sufficient conditions of the NIEP for normal matrices given by Xu [16] and Julio, Manzaneda and Soto [2].
Let $λ_1 \geq λ_2 \geq λ_3 \geq λ_4 \geq λ_5 \geq -λ_1$ be real numbers such that $\sum_{i=1}^5 λ_i =0$. In \cite{oren}, O. Spector prove that a necessary and sufficient condition for $λ_1, λ_2, λ_3, λ_4, λ_5$ to be the eigenvalues of a symmetric nonnegative $5 \times 5$ matrix is "$λ_2+λ_5<0$ and $\sum_{i=1}^5 λ_{i}^{3} \geq 0"$. In this article, we show that this condition is also a necessary and sufficient condition for $λ_1, λ_2, λ_3, λ_4, λ_5$ to be the spectrum of a traceless bisymmetric nonnegative $5 \times 5$ matrix.
We study the bisymmetric nonnegative inverse eigenvalue problem (BNIEP). This problem is the problem of finding the necessary and sufficient conditions on a list of $n$ complex numbers to be a spectrum of an $n \times n$ bisymmetric nonnegative matrix. Most recently, some of the sufficient conditions for the BNIEP are given by Julio and Soto in 2015. In this article, we give another proof of one result (Theorem 4.3) in [Julio and Soto, 2015] and we obtain the result very similar to the one (Theorem 4.2) in [Julio and Soto, 2015] using a different method to construct our desired bisymmetric nonnegative matrix. We also give some sufficient conditions for the BNIEP based on the sufficient conditions for the nonnegative inverse eigenvalue problem (NIEP) given by Borobia in 1995. We give the condition that is both necessary and sufficient for the BNIEP when $n \leq 4$ and then we show that for $n = 6$, the BNIEP and the symmetric nonnegative eigenvalue problem (SNIEP) are different. Moreover, some sufficient conditions for the bisymmetric positive inverse eigenvalue problem are provided. Finally, we give a new result on a sufficient condition for the BNIEP with the prescribed diagonal entries.