multiplication of rows by range in a matrix

i have two matrices

matrix A:

50 44 80 0

50 0 80 52

50 0 80 52

49 49 2 2

matrix B:

5 4 9 7

10 3 10 6

If 1,2,3,4 or 5 is written in matrix b, multiply the last row in matrix A with the first row.

If matrix b says 6 or 7, multiply the last row in matrix A with the second row.

If 8 is written in matrix b, multiply the last row in matrix A with the third row.

However, let him continue this by examining both columns separately. It should return for each row of matrix B.And display them in a new matrix

For example the new matrix:

2450 2156 160 104

2450 132 160 104

Is such a code possible?

Thank u for help

[Voss]

Where does the 132 come from in the new matrix? The only way I can see 132 resulting from multiplying two of the given numbers is A(1,2)*B(2,2) = 44*3 = 132, but the rules don't say anything about multiplying elements from A with elements from B - they always say to multiply elements from two rows of A.

[Berfin Çetinkaya]

True, 132 come from A(1,2)*B(2,2) = 44*3 = 132.

These matrices relate to a real-life problem. So there is no way to multiply these two matrices?

[Torsten]

It's possible, but you stated the rules differently.

Answer 1

[Moksh]

Hi Berfin,

I understand that you have defined two matrices “A” and “B” and defined some multiplication rules to generate a new matrix.

You can try using a “for-loop” with matrix indexing in MATLAB to iterate over the elements of “B” for generating the new resulting matrix.

Since the multiplication rule for “9” and “10” are not specified, I am assuming that the rules for these two are same as when the encountered element is “8”.

Kindly refer to the following code snippet, to perform these operations:

% A and B matrices
A = [50 44 80 0; 50 0 80 52; 50 0 80 52; 49 49 2 2];
B = [5 4 9 7; 10 3 10 6];

% Resulting new matrix
res = zeros(size(B));

% Sizes of A and B
szB = size(B);
szA = size(A);

for i = 1 : szB(1)
    for j = 1 : szB(2)
        row1 = -1;
        row2 = -1;

        if B(i, j) >= 1 && B(i, j) <= 5
            row1 = 1;
            row2 = szA(end);
        end
        
        if B(i, j) >= 6 && B(i, j) <= 7
            row1 = 2;
            row2 = szA(end);
        end

        if B(i, j) >= 8 && B(i, j) <= 10
            row1 = 3;
            row2 = szA(end);
        end

        row_res = A(row1, :) .* A(row2, :);
        res(i, j) = row_res(j);

    end
end

disp(res)

        2450        2156         160         104
        2450        2156         160         104

For more information about indexing arrays and “for-loops”, please refer to the following documentation:

• indexing: https://in.mathworks.com/help/matlab/math/array-indexing.html
• for-loops: https://in.mathworks.com/help/matlab/ref/for.html

Hope this helps resolve the problem.

Best Regards,

Moksh Aggarwal