how do I vectorize a loop with multi-dimensional arrays/ outer product
1 view (last 30 days)
Show older comments
Hi, would someone happen to know how I could vectorize the following loop?
L=4;
for t=1:N;
A(:,:,t)=exp(a*(t-1)).*B(:,:,L);
end
many thanks, Eli
Accepted Answer
Andrei Bobrov
on 21 Jun 2013
B1 = B(:,:,4);
out = reshape(B1(:)*(0:N-1),[size(B1) N]);
3 Comments
James Tursa
on 22 Jun 2013
Edited: James Tursa
on 22 Jun 2013
Your timing is comparing apples to oranges. You preallocate the answer for your loop but do not include it in your timing, whereas you penalize the reshaped outer product by including its intrinsic allocation in the timing. Your loop timing should be this instead, which includes both the allocation and the operations:
tic
C=NaN(128,256,N);
for t=1:N
C(:,:,t)=B(:,:,4)*a(t);
end
toc
Also, the timings should be run several times to make sure background functions are loaded into memory (I assume you do not want the function loading times to bias your results). So don't clear all between timing runs, just clear the variables you allocate (e.g., C, B1, and C1).
More Answers (1)
Iain
on 21 Jun 2013
Edited: Iain
on 21 Jun 2013
A = bsxfun(@times,exp(bsxfun(@times,a,0:(t-1)),B);
You need to make sure that a, 0:t-1 and B are all in the correct dimensions, and that "times", is the correct multiplication for your needs.
A = bsxfun(@times,exp(bsxfun(@times,a,reshape(0:(t-1),1, 1,[]),B);
See Also
Categories
Find more on Creating and Concatenating Matrices in Help Center and File Exchange
Products
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!