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Enclosure of the numerical range of a class of non-selfadjoint rational operator functions. (English) Zbl 06805232

Summary: We introduce an enclosure of the numerical range of a class of rational operator functions. In contrast to the numerical range, the presented enclosure can be computed exactly in the infinite-dimensional case as well as in the finite-dimensional case. Moreover, the new enclosure is minimal given only the numerical ranges of the operator coefficients and many characteristics of the numerical range can be obtained by investigating the enclosure. We introduce a pseudonumerical range and study an enclosure of this set. This enclosure provides a computable upper bound of the norm of the resolvent.

MSC:

47A56 Functions whose values are linear operators (operator- and matrix-valued functions, etc., including analytic and meromorphic ones)
47B28 Nonselfadjoint operators
47A12 Numerical range, numerical radius
47J10 Nonlinear spectral theory, nonlinear eigenvalue problems

Software:

Eigtool

References:

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