Infinite-dimensional features of matrices and pseudospectra

Avijit Pal, Dmitry V. Yakubovich

Given a Hilbert space operator $T$, the level sets of function ${\Psi }_T(z)=\Vert (T-z{)}^{-1}{\Vert }^{-1}$ determine the so-called pseudospectra of $T$. We set ${\Psi }_T$ to be zero on the spectrum of…