How to execute for-loop iterations in parallel

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Vinit Nagda 2022-2-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1641425-how-to-execute-for-loop-iterations-in-parallel

评论： Ive J 2022-2-2

I want to implement parfor to speed up the calculation but I am facing errors.

How can I implement parfor for the following for loop:

I have a 3D matrix X (DIM: mxnxp)

trues=find(X);

for i=1:size(trues,1)

[x,y,z]=ind2sub([m n p],trues(i,1))

if (condition true)

X(x,y,z)=0;

end

Is there any other way I can speed up and optimize execution?

Thank you.

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Benjamin Thompson 2022-2-2

Can you post a working example of sequential MATLAB code that implements your algorithm? You can always set all of X to zeros before the for loop to simplify part of your algorithm. parfor usually cannot write to different locations in a matrix in parallel. You may be able to write the result to an output vector in parfor, then redim the output vector to mxnxp.

Vinit Nagda 2022-2-2

在 MATLAB Online 中打开

m=300;n=300;p=50;
X=ones(m,n,p);
trues=find(X);
for i=1:size(trues,1)
    [x,y,z]=ind2sub([m n p],trues(i,1));
    if (x>y+z)
        X(x,y,z)=0;
    end
end

@Benjamin Thompson Here is the working example. Although the if condition is different in real problem, but algorithm remains same.

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Answer 1

Ive J 2022-2-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1641425-how-to-execute-for-loop-iterations-in-parallel#answer_887305

编辑：Ive J 2022-2-2

在 MATLAB Online 中打开

You don't need even a loop (parfor aside) for this (and I guess you don't even need ind2sub depending on your true purpose here):

m=300; n=300; p=50;
X = ones(m, n, p);
trues = find(X > 0);
[x, y, z] = ind2sub([m n p], trues);
idx = x > y + z;
X(trues(idx)) = 0;

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Vinit Nagda 2022-2-2

@Ive J Thank you for your response. Apparently, in the real problem the if condition check is bit complex rather than simple x > y + z; and therefore requires a loop.

Ive J 2022-2-2