In other words, the square matrix A = [aij] n × n is an
identity matrix, if 
1
0if
if
ij
i
j
a
i
j
=
= 
≠
 We denote the identity matrix of order n by In When order is clear from the
context, we simply write it as I For example [1], 
1
0
0
1





 , 
1
0
0
0
1
0
0
0
1










 are identity matrices of order 1, 2 and 3,
respectively