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matlabmatrixdiagonal

Matrix to Diagonal Matrix in MATLAB

Let's say I have a matrix in MATLAB like

A = [1 2 3; 
     4 5 6; 
     7 8 9]

and I would like to obtain a matrix of the form

B = [1 0 0;  
     0 4 0; 
     0 0 7;
     2 0 0;
     0 5 0;
     0 0 8;
     3 0 0;
     0 6 0;
     0 0 9]

i.e. a matrix that is a concatenation of three diagonal matrices, with each having the columns of matrix A at their diagonals. I know how to do this using a for loop over the columns of A and then concatenating all the results but I am looking for a shorter way to do this. Please share your ideas.

Solution 
  • B(repmat(eye(3),3,1)==1) = A;
reshape(B, [], 3)