For only 3 blocks, it is simplest just to do this.
A = blkdiag([1 1],[1 1],[1 1])
Or, you could do this, if you have more than just 3 blocks. So for 5 blocks, you might do this:
A = kron(eye(5),[1 1])
For many blocks, I would suggest creating a sparse matrix. A simple way of doing that would be to gain use kron, but make one of the pieces sparse.
A = kron(speye(1000),[1 1]);
As you can see, A is a sparse matrix now, so it requires much lles space to store, and many computations using this sparse matrix will be faster.
whos A
spy(A)
