This paper presents a remarkable formula for spectral distance of a given block normal matrix $G_{D_0} = begin{pmatrix} A & B \ C & D_0 end{pmatrix} $ to set of block normal matrix $G_{D}$ (as same as $G_{D_0}$ except block $D$ which is replaced by block $D_0$), in which $A in mathbb{C}^{ntimes n}$ is invertible, $ B in mathbb{C}^{ntimes m}, C in mathbb{C}^{mti...
