Showing math.FAShow all
3 papers · 1 filter
math.FA2025
Numerical Ranges and Spectral Sets: the unbounded case
Michel Crouzeix
It is known that, if C is a convex set containing the numerical range of an operator A, then is a C -spectral set for A with C 1+ $\sqrt$ 2. We impr…
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…
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/d.