Michel Crouzeix

collaborators

4 papers

math.SP2025

Spectral estimates in the quantum annulus and in the numerical annulus

Michel Crouzeix

We improve previous estimates for matrices belonging to the quantum annulus or to the numerical annulus.

math.FA2025

Matrices with invariant by rotation numerical ranges

Michel Crouzeix

We characterize the d x d matrices whose numerical ranges are invariant by rotations of angle 2 $I ¨ $ /d.

math.FA2025

Numerical Ranges and Spectral Sets: the unbounded case

Michel Crouzeix

It is known that, if $I^c ◯$ $\subset$ C is a convex set containing the numerical range of an operator A, then $I^c ◯$ is a C $I^c ◯$ -spectral set for A with C $I^c ◯$ $\leq$ 1+ $\sqrt$ 2. We…

math.FA2025

A New Proof that the Numerical Range is a Complete 2-Spectral Set for Weighted Shift Matrices

Michel Crouzeix, Anne Greenbaum

In this paper we give an alternative proof that the family of matrices studied by Daeshik Choi in A proof of Crouzeix's conjecture for a class of matrices, Linear Algebra and its A…