How to do a quick division between a column array and a matrix?

2 views (last 30 days)
Hello, All,
I want to divid a column array b (N x 1) by each column in a big sparse matrix A (N x M). My code is as follows:
dividCol = zeros(N,M);
for i = 1 : M
nonCol = find(abs(A(:,i))>0);
dividCol(nonCol,i) = b(nonCol)./A(nonCol,i);
end
But it is very slow. I do know if there exist a faster approach to write this code.
Thanks a lot in advance.
Benson

Accepted Answer

Omer Yasin Birey
Omer Yasin Birey on 28 Jan 2019
Edited: Omer Yasin Birey on 28 Jan 2019
Hi Benson, try this
% b = randi(25,25,1);
% A = randi(25,25,5);
[row,col] = find(abs(A(:,:))>0);
dividCol = bsxfun(@rdivide,b(row,1),A(row,col));
  3 Comments
Omer Yasin Birey
Omer Yasin Birey on 28 Jan 2019
Yes I checked the code and it does every operation twice. I had to use loop and updated the code. Try it instead.
% b = randi(25,7,1);
% A = randi(25,7,14);
for i = 1:M
nonCol = find(abs(A(:,i))>0);
dividCol = bsxfun(@rdivide,b(nonCol),A(nonCol,i));
end
Benson Gou
Benson Gou on 28 Jan 2019
Omer,
Thanks for your prompt reply.
Is it possible to do this without using a loop? because loop normally takes more time.
Benson

Sign in to comment.

More Answers (0)

Categories

Find more on Denoising and Compression in Help Center and File Exchange

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!