Jens de Vries

activity

20232026

most citedThe algebraic numerical range as a spectral set in Banach algebras

2 citations · 2 across the 3 of their papers we have counts for

collaborators

3 papers

math.FA2026

Complete functional calculus bounds for $ρ$ -contractions

Michael Hartz, Jens de Vries

Let $T$ be a $ρ$ -contraction on a Hilbert space. We establish sharp bounds for the functional calculus of $T$ for matrix-valued analytic functions on the unit disc. These are compl…

math.FA2024★ 2 cited

The algebraic numerical range as a spectral set in Banach algebras

Hanna Blazhko, Daniil Homza, Felix L. Schwenninger +2

We investigate when the algebraic numerical range is a $C$ -spectral set in a Banach algebra. While providing several counterexamples based on classical ideas as well as combinatori…

math.FA2023

On Abstract Spectral Constants

Felix L. Schwenninger, Jens de Vries

We prove bounds for a class of unital homomorphisms arising in the study of spectral sets, by involving extremal functions and vectors. These are used to recover three celebrated r…

Complete functional calculus bounds for ρ-contractions

The algebraic numerical range as a spectral set in Banach algebras

On Abstract Spectral Constants

Complete functional calculus bounds for $ρ$ -contractions