I have a 3x3 matrix (let's say G) and a 3x3 matrix of zeros (let's say zero). I want a diagonal matrix in the form Diag[G; G; G; zero] such that the size of matrix becomes 12x12. I actually have to add this diagonal matrix to another 12x12 matrix.
I have already tried the solutions of How to form a block-diagonal matrix from a list of matrices? and Create a matrix of matrices using Band and ArrayFlatten but they don't give me a correct result when I check the dimensions of the diagonal matrix. Is there a method that I can use to achieve this result?