Some Extensions of the Crouzeix-Palencia Result

Trevor Caldwell, Anne Greenbaum, Kenan Li

In [{\em The Numerical Range is a $(1+\sqrt{2})$-Spectral Set}, SIAM J. Matrix Anal. Appl. 38 (2017), pp.~649-655], Crouzeix and Palencia show that the numerical range of a squar…