Adding two matrixes with different row numbers.

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

Answer 1

[Stephen Cobeldick]

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

[Santos García Rosado]

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

Answer 2

[Hernia Baby]

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);

[Santos García Rosado]

Thank's Hernia. Your code works fine!