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Question about parfor nested loop

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haonan He
haonan He 2021-1-1
评论： haonan He 2021-1-3
Hi,
I have a question about the nested parfor loop. Please see the following codes:
clc
clear
parfor i=1:3
for j=1:3
if j<2
B(i,j)=j;
end
end
end
The result of this code should be B=[1;1;1], but the Matlab gives B=[1,1,1;1,1,1;1,1,1]. I have been confused by this problem for a long time and thank you in advance if you have some time to look into the problem.
Haonan
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haonan He
haonan He 2021-1-2
Thanks Rik. I reran the code on Matlab 2020b and the result was correct, but it was not as expected when I used old versions, e.g, 2016a 2019a. So maybe it is the bug of the old versions.
haonan He
haonan He 2021-1-2
Thanks Ive. I think the problem may be caused by different versions. When I ran your code on old versions, there was a system error "Index beyond matrix dimension", but it is correct on the lateset version 2020b. So maybe it is the bug of the old versions.

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Matt J
Matt J 2021-1-2
编辑：Matt J 2021-1-2
So maybe it is the bug of the old versions.
Yes, it appears to be version-related. I get the same thing in R2018a. Regardless, it is not good practice to use parfor to loop over sliced variables whose slices, in this case the B(i,:), are not allocated in advance. This cleaner version, for example, does not have the issue:
clc
clear
B=nan(3); %pre-allocate
parfor i=1:3
for j=1:3
if j<2
B(i,j)=j;
end
end
end

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