Question

I have two 9×9 matrices, A and B.

I would like to create a large matrix C with the following pattern

 A B B B B B
 B A B B B B
 B B A B B B
 B B B A B B
 B B B B A B
 B B B B B A

As you can see, the A matrices are on the diagonal, the B are everywhere else. I’m trying to create a code so that this pattern continues no matter how great the dimensions are.

E.g. 10 matrices x 10 matrices still has matrix A along the diagonal and B’s everywhere else.

Best to use horzcat and vertcat or something else like blkdiag? I’d rather not convert these matrices to cells as matrix A and B already contain information.

Thank you everyone for taking the time to read.

Answer 1

How about (refined)

maskcell = repmat( {ones(size(A))}, 1, 10 );
maskdiag = blkdiag( maskcell{:} );
AA = repmat( {A}, 1, 10 );
AD = blkdiag( AA{:} );
BB = repmat( B, 10, 10 );
C = BB .* (maskdiag == 0) + AD

Following on from the entirely valid comments below, I added the ‘mask’ to ensure that the correct pieces are selected from C.