Point spectrum, residual spectrum, and continuous spectrum of unbounded upper triangular operator matrices
Qingmei Bai, Alatancang Chen, Junjie Huang · Thermal Science · 2025
This paper examines the completion of the point spectrum, residual spectrum, and continuous spectrum of an unbounded operator matrix acting in a Hilbert space. The necessary and sufficient conditions for the point spectrum of an unbounded operator matrix to be equal to the union of the point spectra of its diagonal entries are presented.