Reduce the computional time to calculate the mutilplying two matrixes

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Thu Nguyen
Thu Nguyen 2019-5-17
评论： Thu Nguyen 2019-5-17
I calculate this loop for thousands of time.
How can i optimize it to reduce the computational time?
for i=1:n
f(i,:)=w'*Q0(:,:,i)
end
with w =(2000,1) matrix and Q0=(2000,2000,100)
Thanks a lot.
  2 个评论
dpb
dpb 2019-5-17
  1. Preallocate f -- f=zeros(n,numel(w));
  2. Reorient w outside the loop
The first may help enough to be noticeable if haven't; the second is very minor aid to the optimizer and likely will make little, if any, difference.
Thu Nguyen
Thu Nguyen 2019-5-17
Thank you a lot. I also made preallocate and reorient as you made and only reduce little time. I need reduce more such as ~ 100 times.

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回答（1 个）

David Goodmanson
David Goodmanson 2019-5-17
编辑：David Goodmanson 2019-5-17
Hi Thu,
try
% N = 1000;
% M = 200;
Q00 = reshape(Q0,N,N*M);
ff = reshape(w'*Q00,N,M)';
This is approximately four times faster on my PC, compared to the first way with f preallocated.
  1 个评论
Thu Nguyen
Thu Nguyen 2019-5-17
Thank you so much. I found this solution very interesting. But on my PC, it reduce time a little. I want to reduce the computational time about 100 times. Any solution?

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