Some properties of the quartic numerical range for 4x4 operator matrices
Hakimboy M. Latipov · Bulletin of National University of Uzbekistan Mathematics and Natural Sciences · 2023
In the present paper we consider self-adjoint 4x4 operator matrices A. For some special cases the alternative formulas for the calculating the quartic numerical range of 4x4 operator matrices A are derived. Using the obtained alternative formula for the quartic numerical range of A we estimate the lower and upper bound of A.