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

3 vues (au cours des 30 derniers jours)
Atanu
Atanu le 14 Juil 2024
Commenté : Atanu le 16 Juil 2024
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'?

Réponse acceptée

Edric Ellis
Edric Ellis le 15 Juil 2024
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.

Plus de réponses (1)

Drew
Drew le 14 Juil 2024
Modifié(e) : Walter Roberson le 14 Juil 2024
If this answer helps you, please remember to accept the answer
  2 commentaires
Atanu
Atanu le 14 Juil 2024
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 le 14 Juil 2024
It was due to the ending period being interpreted as part of the URL. I have corrected the link.

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