Linear preservers of parallel matrix pairs with respect to the $k$-numerical radius

Bojan Kuzma, Chi-Kwong Li, Edward Poon +1

Let $1\le k<n$ be integers. Two $n\times n$ matrices $A$ and $B$ form a parallel pair with respect to the $k$-numerical radius $w_k$ if $w_k(A+\mu B)=w_k(A)+w_k(B)$ for som…