Matrices in a matrix

I have this matrix in which there are 9 different matrices each one is composed by 6 * 6 elements

I want pre and post multiply each matrix-elements in this way:

A is a matrix with the same size of R

P.S. : I have store R and A as a sparse matrices

How can I do?

Thanks

Answer 1

[David Goodmanson]

Hi UGO, should your top row read R11, R12, R13? at any rate, try

z = zeros(size(A));
C = [A z z;z A z;z z A];
B = C.'*R*C

where C is a block diagonal matrix.

[UGO mela]

It works perfectly!

Thanks!

Answer 2

[John]

try

% if A is 6x6
A = rand(6);
A = repmat(A,3);
% if R is 18x18, constructed from multiple 6x6 sub Rij matrices
B = A'*R*A