MATLAB: Parfor using

parfor time parallel

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.

Best Answer

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
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