Spectral continuity for operator matrices
Spectral continuity for operator matrices
In this paper we prove that if M_C=\pmatrix {AA&#TAB;C\cr00&#TAB;B} is a 2\times 2 upper triangular operator matrix on the Hilbert space H\bigoplus K and if \sigma (A)\cap \sigma (B)=\emptyset , then \sigma is continuous at A and B if and only if \sigma is continuous at M_C, for every C\in …