Dividing a big matrix into small matrices(or Multiply a portion of a matrix to another) to multiply it with a small matrix and after that re add them into the same position.

Question

Syed Yasir Azeem 2022-10-8

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https://ww2.mathworks.cn/matlabcentral/answers/1819925-dividing-a-big-matrix-into-small-matrices-or-multiply-a-portion-of-a-matrix-to-another-to-multiply

评论： Syed Yasir Azeem 2022-10-9

I have a matrix A(400x400) and B(2x2). I want to divide matrix 'A' into 2x2 matrices and multply it with matrix B. Later on Recombine all the matrices from the output into the same locations from where I separated from A.

Example

A = 1 2 3 4 5 6 . . . . B = 1 2

6 5 4 3 2 1 . . . . 3 4

3 2 1 6 5 4 . . . .

5 4 6 1 2 3 . . . .

.

I simple want 1 2 ; 6 5 from A to be multiplied with B and restored in the same position and then multiply 3 4 ; 4 3 with B and so on. I am a beginner. Thank you very much

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Answer 1

KSSV 2022-10-8

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A = [1 2 3 4 5 6 ;                                           
    6 5 4 3 2 1 ;                                                   
    3 2 1 6 5 4 ;
    5 4 6 1 2 3] ;
B = [1 2 ; 3 4] ;
[m,n] = size(A);
k = [2 2];
C = mat2cell(A,k(1)*ones(m/k(1),1),k(2)*ones(n/k(2),1)) ;
[m,n] = size(C) ;
D = cell(m,n) ;
for i = 1:m
    for j = 1:n
        D{i,j} = C{i,j}*B ;
    end
end
iwant = cell2mat(D)
iwant = 4×6
     7    10    15    22    23    34
    21    32    13    20     5     8
     9    14    19    26    17    26
    17    26     9    16    11    16