Only matrices of the same order (same number of rows and same number of columns) may be added by adding corresponding elements.

Example:

1. [2 -3] [7 3] [2 + 7 -3 + 3] [9 0]

[4 5] + [-2 7] = [4 + (-2) 5 + 7] = [2 12]

[6 0] [1 -5] [6 + 1 0 + (-5)] [7 -5]

2. [2 -3] [7 3 5]

[4 5] + [-2 7 -9]

[6 0] [1 -5 0]

The addition above is undefined since the two matrices do not have the same number of columns.