For example 
3
1
0
3
A
3 2
1
42
3
1
−






= 


−


 is a square matrix of order 3 In general, A = [aij] m × m is a square matrix of order m ANote  If A = [aij] is a square matrix of order n, then elements (entries) a11, a22, , ann
are said to constitute the diagonal, of the matrix A