For example
A = [3],     
1
0
B
0
1
−

= 
−


,      
3
0
0
C
0
3
0
0
0
3




= 





are scalar matrices of order 1, 2 and 3, respectively (vi)
Identity matrix
A square matrix in which elements in the diagonal are all 1 and rest are all zero
is called an identity matrix 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