Linear operators that strongly preserves the sign-central matrices
G.Y. Lee, S.G. Lee, Seok-Zun Song · Bulletin of the Korean Mathematical Society · 1997
Let $M_{m,n}$ be the set of all $m \times n$ real matrices. For a matrix $A = [a_{ij}] \in M_{m,n}$, the sign of $a_{ij}$ is defined by $$ sgn a_{ij} = { 0 if a_{ij} = 0, { +1 if a_{ij} > 0, { -1 if a_{ij}