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Any recommendation how to vectorize this double for loop?

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UCL student
UCL student 30 Oct 2014
답변: lvn 31 Oct 2014
I am a beginner in Matlab, and I would like to speed up the following:
X = 100;
MA = NaN(X,3);
for looper = 1:X
compareDist = inf;
array = MM(looper,:);
for looper2 = 1:size(array,1)
currPoint = cell2mat(C(looper,looper2));
currDist = distancePoints3d(pP, currPoint);
compareDist = currDist;
MA(looper,:) = currPoint;
Any help is appreciated. Thanks.

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UCL student
UCL student 31 Oct 2014
MM is just used to measure the size. It should not be in the loop.
per isakson
per isakson 31 Oct 2014
"[MM] should not be in the loop." &nbsp However, in fact it is: &nbsp "array = MM(looper,:)".
Since &nbsp looper &nbsp is a scalar
array = MM(looper,:);
for looper2 = 1:size(array,1)
reduces to
for looper2 = 1:1
Sean de Wolski
Sean de Wolski 31 Oct 2014
How long does it take and how many times do you have to run it?

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lvn 31 Oct 2014
A couple of things:
1. If size(MM(looper,:),1) is independent of looper (as you suggest?), you can simply precalculate it before the loops.
2. Depending on your specific data cell2mat(C(looper,looper2)) can be vectorized by precalculating C2=cell2mat(C); be careful with indexing afterwards though (because all will be merged in one large array). Much easier, if C(looper,looper2) all have the same dimension is to get rid of cells altogether and store your C data in higher dimension matrices.
3. Test for ~isnan(currPoint(1)) before calling distancePoints3d, since if it is NaN the output of distancePoints3d is not used.
4. If you have managed to speed up the code, please post the new code, so we can work on the remainder :)

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