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