A diagonal matrix is called an identity matrix, if all diagonal entries are one, means numeric number 1.if we multiply any matrix on left side or right side the resulting value is same. Multiplicative identity matrix image is:

Called 3 by 3 identity matrix. And

Called 2 by 2 identity matrix. And

Called 1 by 1 identity matrix.

EXAMPLE:

Identity matrix multiply diagonal:

Let A be a matrix. Another matrix B is called identity matrix of A under multiplication if