- Do you have a parallel pool open? I.e. created using parpool, or automatically? If no pool is open then a parfor loop will not be run in parallel anyway.
- Don't use parfor.
Why accessing 2d matrix in parfor so slow?
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Let's say I have a large matrix A:
A = rand(10000,10000);
The following serial code took around 0.5 seconds
tic
for i=1:5
r=9999*rand(1);
disp(A(round(r)+1, round(r)+1))
end
toc
Whereas the following code with parfor took around 47 seconds
tic
parfor i=1:5
r=9999*rand(1);
disp(A(round(r)+1, round(r)+1))
end
toc
How can I speed this up?
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Antworten (1)
Stephen23
am 9 Aug. 2018
Bearbeitet: Stephen23
am 9 Aug. 2018
"How can I speed this up?"
Why do you think that parfor should be faster? The only time that parfor is faster is when the time saved doing the operations in parallel is greater than the overhead required. This topic has been discussed many time on this forum, which also suggest possible improvements to your code:
This is also explained in the documentation:
Your loop contains very fast commands anyway, mostly just round and indexing, so it is quite possible that you will not see any benefit from parfor.
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