Block diagonal matrix from columns

Question

Suppose I have an mxn matrix A .
Is there a way to create B , a (nxm) xn matrix whose "diagonal" is formed by A 's columns ?

Example:

A = [1 2;
     3 4]  

B = [1 0;
     3 0;
     0 2;
     0 4]

Answer 1

Here is a way:

1. Convert A to a cell array of its columns, using mat2cell ;
2. From that cell array generate a comma-separated list , and use it as an input to blkdiag .

Code:

A = [1 2; 3 4];                                   %// example data
C = mat2cell(A, size(A,1), ones(1,size(A,2)));    %// step 1
B = blkdiag(C{:});                                %// step 2

This produces

B =
     1     0
     3     0
     0     2
     0     4

Answer 2

Here is a short script to accomplish this. It works for any dimensions of A.

A=[1 2; 3 4];
[R C] = size(A);

for i=1:C
    B( 1+R*(i-1) : R*i , i ) = A(:,i);
end