How to subsequently adding the matrix from row to row.

Question

Chin 2011-12-15

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/23998-how-to-subsequently-adding-the-matrix-from-row-to-row

I have a matrix

    x = [360   672   467     0     0     0     0     0     0     0
         892   963     0   400     0     0     0     0     0     0
         738   696     0   504   517     0     0     0     0     0
          10     0    20     0    20   840     0     0     0     0]

and another matrix

    y = [0 0 1 2
         0 0 0 0
         0 0 0 4
         3 0 5 6];

The coding that I wrote has some problem when it meet the first row which start at 0. The following is my code.

    %Initialization.
    a = 1;
    z = zeros();
    for t = 1 : size(y, 1)
        for b = 1 : size(y, 2)
            if y(a, b) ~= 0
                z(b) = x(t, y(a, b));
                p = 1;
                for  q = 1 : size(y, 1)
                    if q == 1
                       if y(a, b) ~= 0
                            z(b) = x(t, y(a, b));
                            p = p - 1;
                        end
                    elseif y(a + p, b) ~= 0
                        z(b) = z(b) + x(t, y(a + p, b));
                    end
                    p = p + 1;
                end
            end
        end
        z
    end

How do I get the result such as

0  360  672
0  892 1363
0 1255 1200
0   30  840

what do i missing?

Thank you.

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Answer 1

Andrei Bobrov 2011-12-15

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/23998-how-to-subsequently-adding-the-matrix-from-row-to-row#answer_31483

在 MATLAB Online 中打开

m = size(y,2);
out = zeros(size(x,1),m)
for j1 = 1:m
    out(:,j1) = sum(x(:,nonzeros(y(:,j1))),2);
end

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Chin 2011-12-15

Thank you. Your answer is helpful.

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Answer 2

the cyclist 2011-12-15

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/23998-how-to-subsequently-adding-the-matrix-from-row-to-row#answer_31484

在 MATLAB Online 中打开

x = [360   672   467     0     0     0     0     0     0     0
     892   963     0   400     0     0     0     0     0     0
     738   696     0   504   517     0     0     0     0     0
      10     0    20     0    20   840     0     0     0     0];
y = [0 0 1 2
     0 0 0 0
     0 0 0 4
     3 0 5 6];
z = zeros(size(x,1),size(y,2));
for j = 1:size(y,2)
    ycol = y(:,j);
    idx = ycol(ycol>0);
    z(:,j) = sum(x(:,idx),2);
end