How to resolve warning message about broadcast variable while using 'parfor'?

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Atanu
Atanu 2024-7-14
评论： Atanu 2024-7-16
males = {'animal1', 'animal2', 'animal3'};
treatmentGrps = {'T1', 'T2', 'T3'};
nrows = size(featureLists, 1);
ncols = size(featureLists, 2);
featureLists = cell(nrows, ncols);
parfor grp = 1:nrows
tempRow = cell(1, ncols);
for animal = 1:ncols
tempRow{animal} = individualPsychValuesPerSession('approachavoid', ...
treatmentGrps{grp}, males{animal});
end
featureLists(grp, :) = tempRow;
end
When I use 'parfor' like above I get an warning message
The entire array or structure 'males' is a broadcast variable.
This might result in unnecessary communication overhead.
But, when I change 'ncols' to 'numel(males)' like following
for animal = 1:numel(males)
tempRow{animal} = individualPsychValuesPerSession('approachavoid', ...
treatmentGrps{grp}, males{animal});
end
for the inner loop I don't get any warning.
Can someone please explain this behavior of 'parfor'?

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采纳的回答

Edric Ellis
Edric Ellis 2024-7-15
I think you should ignore this message in this case. It looks like you really need all the values of males for each iteration of the parfor loop, and that's OK. The message is there to warn about cases where the data is being "accidentally" broadcast.
The fact is that the array males is very small (in terms of bytes), so it should not cause significant overhead. You can check using whos to see the size of the array in the workspace, and also use ticBytes and tocBytes to see how much data is being transferred to run the loop. My bet is that the overall data transfer is not being significantly changed by the size of males.

更多回答（1 个）

Drew
Drew 2024-7-14
编辑：Walter Roberson 2024-7-14
See https://www.mathworks.com/help/parallel-computing/broadcast-variable.html It includes an example with numel().
If this answer helps you, please remember to accept the answer
  2 个评论
Atanu
Atanu 2024-7-14
Thanks for your response. But the link is not working for me.
'The page you were looking for is not available in this version of the documentation. You can use the search box or browse the products to find related information. You can also view archived documentation for prior releases.'
Can you share the link again?
Walter Roberson
Walter Roberson 2024-7-14
@Atanu
It was due to the ending period being interpreted as part of the URL. I have corrected the link.

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