i want to make identity matrix

i want to make a matrix that look like this

How could i achieve this efficiently .Thanks in advace

Answer 1

[John D'Errico]

For only 3 blocks, it is simplest just to do this.

A = blkdiag([1 1],[1 1],[1 1])

A = 3×6

1 1 0 0 0 0 0 0 1 1 0 0 0 0 0 0 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])

A = 5×10

1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 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

  Name         Size              Bytes  Class     Attributes

  A         1000x2000            48008  double    sparse    

spy(A)