Fastest pairwise row sums
3 Ansichten (letzte 30 Tage)
Ältere Kommentare anzeigen
Alexander Shtof
am 26 Feb. 2019
Beantwortet: Jos (10584)
am 26 Feb. 2019
I have two matrices A and B, and I would like to compute a matrix C whose rows are all possible combinations of the sum of a row of A and a row of B. What would be the fastest way to perform the computation?
Additional question - what if A and B are both gpuArrays?
Update - Example
Say A is a matrix of 3 rows and B is a matrix of 2 rows, then I would like C to be the matrix
C = [A(1, :) + B(1, :);
A(1, :) + B(2, :);
A(2, :) + B(1, :);
A(2, :) + B(2, :);
A(3, :) + B(1, :);
A(3, :) + B(2, :)];
2 Kommentare
Akzeptierte Antwort
Adam
am 26 Feb. 2019
Bearbeitet: Adam
am 26 Feb. 2019
C = repelem( A, size( B, 1 ), 1 ) + repmat( B, size( A, 1 ), 1 );
Should be the same for gpuArrays too. Whether it is fastest for runtime or not is another matter entirely. There are any number of possible ways of doing it - this is just one. I certainly don't have time to think up, implement and time all of them!
2 Kommentare
Adam
am 26 Feb. 2019
Yeah, it's one of those useful components to know. It is a relatively recent addition, added in R2015a, although the years seem to be flying past so I guess that is already 4 years ago now!
Weitere Antworten (1)
Jos (10584)
am 26 Feb. 2019
% An old-school 20th century indexing trick:
A = randi(9,3,2)
B = 100*randi(9,4,2)
[ia, ib] = ndgrid(1:size(A,1),1:size(B,1))
C = A(ia,:) + B(ib,:)
0 Kommentare
Siehe auch
Kategorien
Mehr zu Matrices and Arrays finden Sie in Help Center und File Exchange
Produkte
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!