On the point and residual spectrum of the operator matrix MX
Dragana S. Cvetković‐Ilić, Vladimir Pavlović · Linear and Multilinear Algebra · 2016
In this paper, for given operators , and , we completely describe the set of all such that the operator is injective, in the case when is closed. Then, we give necessary and sufficient conditions for the existence of some such that is not dense in . The results are then used to draw some additional conclusions about the residual spectrum of the operator matrix .