I need to combine those three martix into a single big one. How do I do that?

Answer 1

[Voss]

See blkdiag:

https://www.mathworks.com/help/matlab/ref/blkdiag.html

Answer 2

[David Hill]

blkdiag(randi(10,2),randi(10,2),randi(10,2))

ans = 6×6

8 9 0 0 0 0 8 7 0 0 0 0 0 0 2 6 0 0 0 0 1 4 0 0 0 0 0 0 4 8 0 0 0 0 10 9