how can i multiply blocks of a block matrix by a non block-matrix, block to elements?

i want multiply blocks of a block matrix by a non block matrix as size of the block matrix is same under blocks, with size non block matrix under elements. for example :

     1     0     1     0                         2   0   3   0 
     0     1     0     1                         0   2   0   3
     1     0     1     0         2     3         4   0   5   0  
                          *      4     5      =  0   4   0   5     
     0     1     0     1

Answer 1

[BhaTTa]

Hey @xosro, I assume that you want to multiply each 2x2 block of A by a corresponding element from B. The element B(i, j) should multiply the block in A located at the same block position. Please refer to below sample code which does the same, please make sure to modify it based on your requirement:

% Block matrix A
A = [1 0 1 0;
     0 1 0 1;
     1 0 1 0;
     0 1 0 1];

% Non-block matrix B
B = [2 3;
     4 5];

% Size of the block
blockSize = 2;

% Initialize the result matrix C
C = zeros(size(A));

% Loop over each block in A
for i = 1:blockSize:size(A, 1)
    for j = 1:blockSize:size(A, 2)
        % Determine the block index
        blockRow = (i-1)/blockSize + 1;
        blockCol = (j-1)/blockSize + 1;
        
        % Extract the block from A
        blockA = A(i:i+blockSize-1, j:j+blockSize-1);
        
        % Multiply the block by the corresponding element in B
        C(i:i+blockSize-1, j:j+blockSize-1) = blockA * B(blockRow, blockCol);
    end
end

% Display the result
disp('Resulting matrix C:');
disp(C);