# How to execute for-loop iterations in parallel

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Vinit Nagda on 2 Feb 2022
Commented: Ive J on 2 Feb 2022
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.
##### 2 CommentsShowHide 1 older comment
Vinit Nagda on 2 Feb 2022
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.

Ive J on 2 Feb 2022
Edited: Ive J on 2 Feb 2022
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;
##### 2 CommentsShowHide 1 older comment
Ive J on 2 Feb 2022
Maybe you can explain the probelm itself then :)

R2020b

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