How to get the diagonal and a subdiagonal in the same matrix?

I'm trying to get matrix that only has the diagonal and the first subdiagonal values only. Say I have a 4x4 matrix

A=[ 1  2  3  4;
    5  6  7  8;
    9 10 11 12;
   13 14 15 16]

I want to get a matrix

B=[1 2  0  0;
   0 6  7  0;
   0 0 11 12;
   0 0  0 16].

I know using

diag(diag(A))

will give me a 4x4 matrix with the diagonal but the part I'm hung up on is getting the subdiagonal in the form of a 4x4 matrix, I used

diag(diag(A,1))

and it gave me a 3x3 matrix of the subdiagonal. To conclude, is there a way of getting a subdiagonal in the original matrix dimensions?

Answer 1

[Mohammad Abouali]

A=[ 1  2  3  4;
    5  6  7  8;
    9 10 11 12;
   13 14 15 16]

B=triu(A)-triu(A,2)

B =

       1     2     0     0
       0     6     7     0
       0     0    11    12
       0     0     0    16

[Jose]

Thank you, much appreciated!

[Mohammad Abouali]

you are welcome