Spectral approximations of unbounded operators of the type ``normal plus compact''
The author investigates the spectral approximation of the operator \(A=S+B\), where \(S\) is a normal operator in the separable Hilbert space \(H\) with compact resolvent and \(B\) is a compact operator in \(H\). Namely, he studies the approximations of the eigenvalues of the operator \(A\) by the eigenvalues of the operators \(A_n=S+B_n\), \(n=1,2,\dots\), where \(B_n\) are \(n\)-dimensional operators. An error estimate of the approximation is also obtained.
scientific article; zbMATH DE number 6361353
scientific article