Another proof of a conjecture of marcus on thec-numerical range
Natália Bebiano, João da Providência · Linear and Multilinear Algebra · 1996
Let A be an n × n complex matrix andc = (γ1, …, γ n ) t ∊Cn. The c-numerical range of A is the set In this note we present another proof of a result of Au-Yeung and Tsing concerning the convexity of Wc (A), which answers a conjecture of Marcus. A new proof of the concavity of the boundary of Wc (A) at regular points, for A normal, is also given.