TY - JOUR
TI - Point spectrum, residual spectrum, and continuous spectrum of unbounded upper triangular operator matrices
AU - Bai Qingmei
AU - Chen Alatancang
AU - Huang Junjie
JN - Thermal Science
PY - 2025
VL - 29
IS - 3
SP - 1811
EP - 1820
PT - Article
AB - 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.