4 papers
Enclosure of the Numerical Range and Resolvent Estimates of Non-selfadjoint Operator Functions
Axel Torshage
In this paper we discuss the relationship between the numerical range of an extensive class of unbounded operator functions and the joint numerical range of the operator coefficien…
Accumulation of Complex Eigenvalues of a Class of Analytic Operator Functions
Christian Engström, Axel Torshage
For analytic operator functions, we prove accumulation of branches of complex eigenvalues to the essential spectrum. Moreover, we show minimality and completeness of the correspond…
On Equivalence and Linearization of Operator Matrix Functions with Unbounded Entries
Christian Engström, Axel Torshage
In this paper we present equivalence results for several types of unbounded operator functions. A generalization of the concept equivalence after extension is introduced and used t…
Enclosure of the Numerical Range of a Class of Non-Selfadjoint Rational Operator Functions
Christian Engström, Axel Torshage
In this paper 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…