3 papers
math.FA2025
Contractive upper triangular matrices with prescribed diagonals and superdiagonals
Axel Renard
A characterization of the matrix representation of the compressed shift acting on a finite-dimensional model space endowed with the Takenaka-Malmquist-Walsh basis, among all upper…
math.FA2025
A criterion of contractivity for four by four upper-triangular matrices
Axel Renard
We establish an explicit criterion for determining whether a upper-triangular matrix is a contraction with respect to the Euclidean operator norm.
math.FA2024
Schwarz-Pick type inequalities from an operator theoretical point of view
Catalin Badea, Axel Renard
We use (versions of) the von Neumann inequality for Hilbert space contractions to prove several Schwarz-Pick inequalities. Specifically, we derive an alternate proof for a multi-po…