Normality and the Higher Numerical Range
Marvin D. Marcus, B. N. Moyls, Ivan Filippenko · Canadian Journal of Mathematics · 1978
Let Mn(C) be the vector space of all w-square complex matrices. Denote by (• , •) the standard inner product in the space C n of complex n-tuples. For a matrix A ∈ Mn(C) and an n-tuple c = (c1,… , cn) ∈ C n, define the c-numerical range of A to be the set