The generalizedK- numerical range
Yiu‐Tung Poon · Linear and Multilinear Algebra · 1980
Let U n be the set of all n×n unitary matrices and A an n×n normal matrix. For any 1 k n, denote the n× n matrix (aij ) with aii =1 for all 1 i k and all other entries 0 by In,k . In this note, the author gives a necessary and sufficient condition for the set to be convex.