Example

> a = rand(3,5)
 a =
        1      0.333      0.665      0.167       0.91  
    0.975     0.0369     0.0847      0.655      0.112  
    0.647      0.162      0.204      0.129      0.299  
> diag(a)
        1  
   0.0369  
    0.204  
> diag(a,0)
        1  
   0.0369  
    0.204  
> diag(a,-1)
    0.975  
    0.162  
> diag(a,2)
    0.665  
    0.655  
    0.299  
> b = 1:3
 b =
        1          2          3  
> diag(b)
        1          0          0  
        0          2          0  
        0          0          3  
> diag(b,1)
        0          1          0          0  
        0          0          2          0  
        0          0          0          3  
        0          0          0          0