Combination of rows of two different matrices
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Sorry if this is a repeated question but I failed to find an answer myself. I have two matrices:
A = [-0.6, -0.2;
-60, 2;
6, -20];
B = [-0.4, -0.8;
-40, 8;
4, -80];
I want to find all the possible combinations of sum of each row (sum of individual elements of a row) of A with each row of B, i.e., my desired result is (order does not matter):
ans = [-1, -1;
-40.6, 7.8;
3.4, -80.2;
-60.4, 1.2;
-100, 10;
-56, -78;
5.6, -20.8;
-34, -12;
10, -100];
which is a matrix resulting from possible combinations of A and B.
Thanks in advance.
(Please no for loops. It is pretty trivial then.)
EDIT: I have used 2 columns and 3 rows as an example. Looking for more general solution, i.e., for n number of columns and m number of rows.
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Accepted Answer
Fangjun Jiang
on 23 Jul 2020
Edited: Fangjun Jiang
on 23 Jul 2020
Feels non-ideal. Any better solution?
>> C=A(:,1)+B(:,1)';
D=A(:,2)+B(:,2)';
reshape([C(:),D(:)],[],2)
ans =
-1.0000 -1.0000
-60.4000 1.2000
5.6000 -20.8000
-40.6000 7.8000
-100.0000 10.0000
-34.0000 -12.0000
3.4000 -80.2000
-56.0000 -78.0000
10.0000 -100.0000
better one
>> m=size(A,1);
ind1=repmat(1:m,1,m);
ind2=repelem(1:m,m);
A(ind1,:)+B(ind2,:)
ans =
-1.0000 -1.0000
-60.4000 1.2000
5.6000 -20.8000
-40.6000 7.8000
-100.0000 10.0000
-34.0000 -12.0000
3.4000 -80.2000
-56.0000 -78.0000
10.0000 -100.0000
More Answers (1)
Bruno Luong
on 23 Jul 2020
Edited: Bruno Luong
on 23 Jul 2020
A = [-0.6, -0.2;
-60, 2;
6, -20];
B = [-0.4, -0.8;
-40, 8;
4, -80];
Single statement
reshape(permute(A,[3 1 2])+permute(B,[1 3 2]),[],size(A,2))
or a variation
reshape(reshape(A,1,size(A,1),[])+reshape(B,size(B,1),1,[]),[],size(A,2))
Gives
ans =
-1.0000 -1.0000
-40.6000 7.8000
3.4000 -80.2000
-60.4000 1.2000
-100.0000 10.0000
-56.0000 -78.0000
5.6000 -20.8000
-34.0000 -12.0000
10.0000 -100.0000
>>
3 Comments
Bruno Luong
on 23 Jul 2020
Yes the variation version does no more no less than the required combination sums and puts at the results at the right place. Not a hair uneccesary arithmetic or memory moving (first version).
Fangjun Jiang
on 24 Jul 2020
Brilliant, Bruno Luong! I learned implicit expansion in a whole new dimension.
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