Matrices with hyperbolical Krein space numerical range
Natália Bebiano, Rute Lemos, Graça Soares · Advances in Operator Theory · 2024
Abstract This paper is devoted to matrices with hyperbolical Krein space numerical range. This shape characterizes the 2-by-2 case and persists for certain classes of matrices, independently of their size. Necessary and sufficient conditions for low dimensional tridiagonal matrices to have this shape are obtained involving only the matrix entries.