Why is my parfor loop not running?

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Marc Laub 2020-6-10

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https://ww2.mathworks.cn/matlabcentral/answers/545741-why-is-my-parfor-loop-not-running

评论： Edric Ellis 2020-6-11

Hello,

I guess this question has been asked multiple times. I did all the troubleshooting before but I still dont undersatdn why my following parfor loop wont run.

seeds=NaN(volume/4*num_pts,3,volume/4);
parfor i=1:volume/4
    
    pts=partial_seeder(min_grain,num_pts);
    ptRads = seeder(pts);
    
    seeds(:,1:2,i)=pts;
    seeds(:,3,i)=ptRads;
    
end
function pts=partial_seeder(min_grain,num_pts)
pts=NaN(num_pts,2);
pts(1,:)=rand(1,2)*2*10^-3; 
id=2;
while id<=num_pts
   pts_new=rand(1,2)*2*10^-3; 
   
   d=pdist2(pts_new,pts(1:id-1,:));
   
   if min(d)>=min_grain
       pts(id,:)=pts_new;
       id=id+1;
   else
       continue
   end
end
end

I preallocated my array seeds and I dont know why Matlab would be unable to classify my variable seeds. It should just calculate the functions partial_seeder and seeder in parallel and write the results into seeds... not sure why it wont work.

Many Thanks in advance

best regards

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Edric Ellis 2020-6-11

As it happens, I already provided the answer to this question before I'd even seen the question - see here https://www.mathworks.com/matlabcentral/answers/545921-how-to-use-fetchnext-correctly . Basically, this is a parfor slicing constraint - you're not allowed two different assignment expressions into seeds - you have to make a temporary variable for each iteration of the parfor loop so that you can make only a single assignment.

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