Matrix manipulation problem under MATLAB

I want to put a matrix A in another matrix B

example

A= 0 2 9

5 7 3

4 6 1

B= 0 2 9 0 0 0

5 7 3 0 0 0

4 6 1 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

0 0 0 0 0 0

and a C matrix in another place

C= 1 2 3

4 5 6

7 8 9

B= 0 2 9 0 0 0

5 7 3 0 0 0

4 6 1 0 0 0

0 0 0 1 2 3

0 0 0 4 5 6

0 0 0 7 8 9

Answer 1

[Adam]

A = [0 2 9; 5 7 3; 4 6 1];
C = [1 2 3; 4 5 6; 7 8 9];

B = zeros(6);
B(1:3,1:3) = A;
B(4:6,4:6) = C;

[dakhli mohamed]

I want to redo the same work but with a matrix of size 284 * 284

what should I do

[Adam]

Just extend it in the obvious way based on whatever you want to insert.

Answer 2

[Guillaume]

Possibly, you're looking for blkdiag:

A = [0 2 9; 5 7 3; 4 6 1];
C = [1 2 3; 4 5 6; 7 8 9];
B = blkdiag(A, C)