How do I find the additive identity matrix?

The sum between two matrices can be done if and only if the two matrices are similar, that means that they have the same numbers of rows and columns.

Also the additive has to be similar to the other, so every shape of matrix has its identity matrix.

The elements, obviously, are all .

E.G.

The matrix with the shape: 3 rows and 4 columns has this identity matrix:

##0000## ##0000## ##0000##