MATLAB: Create a block diagonal matrix with same repeating block

matlab matrix vectorization
steadyfish picture steadyfish · May 4, 2013 · Viewed 17k times · Source

I have a matrix K of dimensions n x n. I want to create a new block diagonal matrix M of dimensions N x N, such that it contains d blocks of matrix K as its diagonal.

I would have directly used M = blkdiag(K,K,K) etc. had d been smaller. Unfortunately, d is very large and I don't want to manually write the formula with d exactly same arguments for the blkdiag() function.

Is there any shorter, smarter way to do this?

Answer

bla picture bla · May 4, 2013

you can use kron for that. 

M = kron(X,Y)

returns the Kronecker tensor product of X and Y. The result is a large array formed by taking all possible products between the elements of X and those of Y. If X is m-by-n and Y is p-by-q, then kron(X,Y) is m*p-by-n*q. So in your case something like this will do:

M = kron(eye(L),K)

with L the # of blocks.

Related questions

How can I apply a function to every row/column of a matrix in MATLAB?

You can apply a function to every item in a vector by saying, for example, v + 1, or you can use the function arrayfun. How can I do it for every row/column of a matrix without using a for loop?

Read More
How do I compare all elements of two arrays?

I have two big arrays with about 1000 rows and 1000 columns. I need to compare each element of these arrays and store 1 in another array if the corresponding elements are equal. I can do this with for loops but that takes …

Read More
Multiply a 3D matrix with a 2D matrix

Suppose I have an AxBxC matrix X and a BxD matrix Y. Is there a non-loop method by which I can multiply each of the C AxB matrices with Y?

Read More