5 citations · 5 across the 4 of their papers we have counts for
Showing 2015 · math.FAShow all
3 papers · 2 filters
math.FA2015
Non-commutativity of exponential spectrum
Hubert Klaja, Thomas Ransford
In a Banach algebra, the spectrum satisfies for each pair of elements . We show that this is no longer true for the exponential spe…
math.FA2015
On mapping theorems for numerical range
Hubert Klaja, Javad Mashreghi, Thomas Ransford
Let be an operator on a Hilbert space with numerical radius . According to a theorem of Berger and Stampfli, if is a function in the disk algebra such that $f…
math.FA2015
Rank one perturbations of diagonal operators without eigenvalues
Hubert Klaja
In this paper, we prove that every diagonal operator on a Hilbert space of which is of multiplicity one and has perfect spectrum admits a rank one perturbation without eigenvalues.…