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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.