Numerical ranges of conjugations and antilinear operators
Injo Hur, Ji Eun Lee · Linear and Multilinear Algebra · 2019
In this paper, we examine the numerical ranges of conjugations and antilinear operators, which will be shown to be annuli in general. This result indicates that Toeplitz–Hausdorff Theorem, which says the convexity on the numerical ranges of linear operators, does not hold for the ones of antilinear operators.