1
0
0
C
0
2
0
0
0
3
−



= 





, are diagonal matrices
of order 1, 2, 3, respectively (v)
Scalar matrix
A diagonal matrix is said to be a scalar matrix if its diagonal elements are equal,
that is, a square matrix B = [bij] n × n is said to be a scalar matrix if
bij = 0,    when i  ≠ j
bij = k,    when i  = j, for some constant k 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