parfor using

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N. Yildirim
N. Yildirim 2012-3-3
Hi everybody, i have a question about parfor using. I tried a classical example for parfor on my PC but i couldn't get gainly results. How ?
nmax=1000;
y = zeros(nmax,1);
tic
parfor n = 1:nmax
z = randn(n);
y(n) = max(svd(z));
end
toc
Results:
(nmax, pool size, time)
(500, 0, 12.51) (500, 2, 8.71) (500, 4, 5.16) That's OK.
(750, 0, 46.03) (750, 2, 38.65) (750, 4, 30.32) Maybe OK.
(1000, 0, 141.40) (1000, 2, 156.19) (1000, 4, 174.81) Why ?
Thanks for replies.

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采纳的回答

Laurens Bakker
Laurens Bakker 2012-3-7
Hi Yildirim,
There is considerable overhead in gathering the data back into a single variable. I removed the assignments and that improves the situation.
nmax=1000;
y = zeros(nmax,1);
tic
parfor n = 1:nmax
max( svd( randn(n) ));
end
toc
Cheers,
Laurens

更多回答（1 个）

N. Yildirim
N. Yildirim 2012-3-17
Hi Laurens,
thanks a lot for your reply. It's also very logical to me. But I havent still time saving. Nothing has changed :(
Cheers, Yildirim

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