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How to execute for-loop iterations in parallel

조회 수: 6 (최근 30일)
Vinit Nagda
Vinit Nagda 2022년 2월 2일
댓글: Ive J 2022년 2월 2일
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
end
Is there any other way I can speed up and optimize execution?
Thank you.
  댓글 수: 2
Benjamin Thompson
Benjamin Thompson 2022년 2월 2일
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
Vinit Nagda 2022년 2월 2일
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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답변 (1개)

Ive J
Ive J 2022년 2월 2일
편집: Ive J 2022년 2월 2일
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;
  댓글 수: 2
Vinit Nagda
Vinit Nagda 2022년 2월 2일
@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
Ive J 2022년 2월 2일
Maybe you can explain the probelm itself then :)

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