Wrong indexing in parfor loop

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Andre Zeug
Andre Zeug 2015 年 11 月 10 日
編集済み: Andre Zeug 2015 年 11 月 11 日
I tried to use parfor to change parts of a variable but receive unexpected result
d = ones(10,10);
d = repmat(d,[1 1 1 10]);
d(:,:,2,:) = .5*d(:,:,1,:);
parfor n=1:10;
d(:,:,2,n) = 2*d(:,:,2,n);
end
I expected to receive something like
d(:,:,2,:) = d(:,:,1,:);
Instead I get
d(:,:,1,:) = 2;
d(:,:,2,:) = .5;
What went wrong? Using for instead of parfor works fine.
Thanks
  5 件のコメント
Andre Zeug
Andre Zeug 2015 年 11 月 10 日
編集済み: Andre Zeug 2015 年 11 月 10 日
I could now reproduce this unexpected result also on R2013b.

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回答 (1 件)

Andre Zeug
Andre Zeug 2015 年 11 月 11 日
編集済み: Andre Zeug 2015 年 11 月 11 日
Thanks to the community. Summarizing, the problem of wrong indexing in PARFOR loops appears in R2014a (and older versions?) but is not an issue in R2015a and later.
Here a simple workaround for Matlab users with releases before introduction of HG2:
d = ones(10,10,10,10);
% slice variable
dSub = d(:,:,2,:);
% if memory is an issue
d(:,:,2,:) = [];
parfor n=1:10;
% do manipulation to subset only
dSub(:,:,:,n) = 2*dSub(:,:,:,n);
end
% if memory is an issue
d(:,:,[1 3:10],:) = d;
% include the manipulated part
d(:,:,2,:) = dSub;
clear dSub

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