Talks

I will give a short summary of my master thesis as well as a quick introduction of myself.

Was wird aus (Pseudo-)Eigenwerten und -vektoren beim Abschneiden einer unendlichen Matrix? (Sie bleiben welche.)
Gibt es auch Aussagen in die umgekehrte Richtung?
Wie gut lassen sich diese Aussagen quantifizieren?

Talk (PDF, 1.0MB)

We construct extrapolation spaces for non-densely defined (weak) Hille--Yosida operators. In particular, we discuss extrapolation of bi-continuous semigroups. As an application we present a Desch--Schappacher type perturbation result for this kind of semigroups. This talk is based on joint work with B. Farkas.

For two Banach spaces $X,Y$ let $u:\mathbb{R}_{\geq 0}\rightarrow \mathcal{L}(X;Y)$ be an operator valued function and $\mathtt{P}$ a regularity property. Assume that each orbit $t\mapsto u(t)x$ has the regularity property $\mathtt{P}$ on some interval $(t_x,\infty)$ in general depending on $x\in X$. In this paper we prove a Baire-type theorem, which allows to remove the dependency of $x$ in certain situations. Afterwards, we provide some applications which are of interest in semigroup theory. In particular, we generalize and explain the result obtained by Bárta in his article ``\emph{Two notes on eventually differentiable families of operators}'' (Comment. Math. Univ. Carolin. 51,1 (2010), 19-24).

In this presentation we will talk about the application of hierarchical matrices to solve the least squares problem arising in the RBF Approximation of scattered data.

We will shortly introduce hierarchical matrices as well as some central aspects of the RBF approach to scattered data. The main part will be about different ideas regarding the QR decomposition of hierarchical matrices.