Numerical Ranges and Spectral Sets: the unbounded case
Michel Crouzeix
公開日: 2025/9/24
Abstract
It is known that, if $\Omega$ $\subset$ C is a convex set containing the numerical range of an operator A, then $\Omega$ is a C $\Omega$ -spectral set for A with C $\Omega$ $\le$ 1+ $\sqrt$ 2. We improve this estimate in unbounded cases.