Essential numerical ranges of linear operators and applications to PDEs

Wann
Donnerstag, 2. Februar 2023

Wo

Veranstaltet von

Vortragende Person/Vortragende Personen:
Christiane Tretter, University of Bern, CH

Abstract: In this talk the concept of essential numerical range for unbounded Hilbert space operators is introduced and studied, including possible equivalent characterizations and perturbation results. Compared to the bounded case, new interesting phenomena arise which we illustrate by some striking examples. A key feature of the essential numerical range is that it captures, in a unified and minimal way, spectral pollution which is an unwanted effect e.g. when approximating PDEs by projection methods or domain truncation methods.