On the shape of the generalized numerical ranges
Nam‐Kiu Tsing · Linear and Multilinear Algebra · 1981
Let A be an n × n complex matrix. For 1 ≤ k ≤ n, let Λ k be the set of all k-tuples of orthonormal vectors in ¢ n and ck = (γ1,…,γ k ) ε ¢ k . In this note, it is proved that the sets and are star-shaped.