how do I vectorize a loop with multi-dimensional arrays/ outer product
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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
Risposta accettata
Andrei Bobrov
il 21 Giu 2013
B1 = B(:,:,4);
out = reshape(B1(:)*(0:N-1),[size(B1) N]);
3 Commenti
James Tursa
il 22 Giu 2013
Modificato: James Tursa
il 22 Giu 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).
Più risposte (1)
Iain
il 21 Giu 2013
Modificato: Iain
il 21 Giu 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);
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