Adding two matrixes with different row numbers.

Question

Santos García Rosado 2021-2-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/756964-adding-two-matrixes-with-different-row-numbers

评论： Santos García Rosado 2021-2-26

Hi Mathworks community!

I have a matrix A(mxn) and a matrix B(lxn) such as:

A = [1,2,3,4,5,6,7,8,9,10; 10,11,12,13,14,15,16,17,18,19; 19,20,21,22,23,24,25,26,27,28];
B = [1,2,3,4,5,6,7,8,9,10; 2,4,6,8,10,12,14,18,18,20];

I'd like to get an output such as:

out = [sum(A(1,:),B(1,:)); sum(A(1,:),B(2,:)); sum(A(2,:),B(1,:)); sum(A(2,:),B(2,:)); sum(A(3,:),B(1,:)); sum(A(3,:),B(2,:))];

Any idea about how I could code this efficiently?

Thank's in advance!

Santos García

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Answer 1

Stephen23 2021-2-26

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https://ww2.mathworks.cn/matlabcentral/answers/756964-adding-two-matrixes-with-different-row-numbers#answer_633989

A = [1,2,3,4,5,6,7,8,9,10; 10,11,12,13,14,15,16,17,18,19; 19,20,21,22,23,24,25,26,27,28];
B = [1,2,3,4,5,6,7,8,9,10; 2,4,6,8,10,12,14,18,18,20];
[Y,X] = ndgrid(1:size(B,1),1:size(A,1));
out = A(X(:),:) + B(Y(:),:)
out = 6×10
     2     4     6     8    10    12    14    16    18    20
     3     6     9    12    15    18    21    26    27    30
    11    13    15    17    19    21    23    25    27    29
    12    15    18    21    24    27    30    35    36    39
    20    22    24    26    28    30    32    34    36    38
    21    24    27    30    33    36    39    44    45    48

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Santos García Rosado 2021-2-26

Great Stephen! I really appreciate avoiding a loop. Thank's for the help!

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Answer 2

Hernia Baby 2021-2-26

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/756964-adding-two-matrixes-with-different-row-numbers#answer_633979

Following your output image,

out = [sum(A(1,:),B(1,:)); sum(A(1,:),B(2,:)); sum(A(2,:),B(1,:)); sum(A(2,:),B(2,:)); sum(A(3,:),B(1,:)); sum(A(3,:),B(2,:))];

the code is like below

A = [1,2,3,4,5,6,7,8,9,10; 10,11,12,13,14,15,16,17,18,19; 19,20,21,22,23,24,25,26,27,28];
B = [1,2,3,4,5,6,7,8,9,10; 2,4,6,8,10,12,14,18,18,20];
A_sum = sum(A,2);
B_sum = sum(B,2);
for i = 1:length(A_sum)
    for j = 1:length(B_sum)
        C(i,j) = A_sum(i) + B_sum(j);
    end
end
out = rehape(C,[],1);