Wrong indexing in parfor loop

1 次查看（过去 30 天）

Andre Zeug 2015-11-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/254098-wrong-indexing-in-parfor-loop

编辑： Andre Zeug 2015-11-11

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 个评论
显示 3更早的评论隐藏 3更早的评论

Adam Barber 2015-11-10

I was able to reproduce this on R2014a, but not R2015b on my system.

Andre Zeug 2015-11-10

编辑：Andre Zeug 2015-11-10

I could now reproduce this unexpected result also on R2013b.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Andre Zeug 2015-11-11

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/254098-wrong-indexing-in-parfor-loop#answer_199331

编辑：Andre Zeug 2015-11-11

在 MATLAB Online 中打开

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