Weyl spectra of operator matrices
Weyl spectra of operator matrices
In this paper it is shown that if $M_{C}=\left (\begin {smallmatrix}A&C 0&B\end {smallmatrix} \right )$ is a $2\times 2$ upper triangular operator matrix acting on the Hilbert space $\mathcal {H}\oplus \mathcal {K}$ and if $\omega (\cdot )$ denotes the "Weyl spectrum", then the passage from $\omega (A)\cup \omega (B)$ to …