Zero Matrices - Expii

The "m-by-n zero matrix" is just the m×n matrix 0{m,n} with all entries 0. For any m×n matrix A, the sum A + 0{m,n} is just A, and there is an "additive inverse" -A (with the sign of every entry of A flipped) so that A + (-A) = 0_{m,n}.