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math.SP2019
Essential numerical ranges for linear operator pencils
Sabine Bögli, Marco Marletta
We introduce concepts of essential numerical range for the linear operator pencil . In contrast to the operator essential numerical range, the pencil essential numer…
math.SP2019
The essential numerical range for unbounded linear operators
Sabine Bögli, Marco Marletta, Christiane Tretter
We introduce the concept of essential numerical range for unbounded Hilbert space operators and study its fundamental properties including possible equivalent char…