A conjecture of marcus on the generalized numerical range
Yik-Hoi Au-Yeung, Nam‐Kiu Tsing · Linear and Multilinear Algebra · 1983
Let A be an n × n complex normal matrix with eigenvalues . In the present paper the authors show that if are not collinear, then the set is an orthonormal sct in is not convex which answers a conjecture posed by Marcus concerning the convexity of the generalized numerical range.