7 papers
Computing Klein-Gordon Spectra
Frank Rösler, Christiane Tretter
We study the computational complexity of the eigenvalue problem for the Klein-Gordon equation in the framework of the Solvability Complexity Index Hierarchy. We prove that the eige…
Everything is possible for the domain intersection dom T \cap dom T*
Yury Arlinskii, Christiane Tretter
This paper shows that for the domain intersection $\dom T\cap\dom T^*$ of a closed linear operator and its Hilbert space adjoint everything is possible for very common classes of o…
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…
On a spectral problem in magnetohydrodynamics and its relevance for the geodynamo
Frank Stefani, Christiane Tretter
One of the most remarkable features of the geodynamo is the irregular occurrence of magnetic field reversals. Starting with the operator theoretical treatment of a non-selfadjoint…
The damped wave equation with unbounded damping
Pedro Freitas, Petr Siegl, Christiane Tretter
We analyze new phenomena arising in linear damped wave equations on unbounded domains when the damping is allowed to become unbounded at infinity. We prove the generation of a cont…
Numerical Range and Quadratic Numerical Range for Damped Systems
Birgit Jacob, Christiane Tretter, Carsten Trunk +1
We prove new enclosures for the spectrum of non-selfadjoint operator matrices associated with second order linear differential equations $\ddot{z}(t) + D \dot{z} (t) + A_0 z(t) = 0…