181 citations · 771 across the 48 of their papers we have counts for
5 papers · 1 filter
A distance between operators acting in different Hilbert spaces and operator convergence
Olaf Post, Jan Simmer
The aim of the present article is to give an introduction to the concept of quasi-unitary equivalence and to define several (pseudo-)metrics on the space of self-adjoint operators…
Generalised norm resolvent convergence: comparison of different concepts
Olaf Post, Sebastian Zimmer
In this paper, we show that the two concepts of generalised norm resolvent convergence introduced by Weidmann and the first author of this paper are equivalent. We also focus on th…
On a generalisation of Krein's example
Olaf Post, Christoph Uebersohn
We generalise a classical example given by Krein in 1953. We compute the difference of the resolvents and the difference of the spectral projections explicitly. We further give a f…
Boundary pairs associated with quadratic forms
Olaf Post
We introduce an abstract framework for elliptic boundary value problems in a variational form. Given a non-negative quadratic form in a Hilbert space, a boundary pair consists of a…
Convergence of sectorial operators on varying Hilbert space
Delio Mugnolo, Robin Nittka, Olaf Post
Convergence of operators acting on a given Hilbert space is an old and well studied topic in operator theory. The idea of introducing a related notion for operators acting on aryin…