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Any recommendation how to vectorize this double for loop?

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UCL student
UCL student am 30 Okt. 2014
Geschlossen: MATLAB Answer Bot am 20 Aug. 2021
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);
if(~isnan(currPoint(1))&&currDist<compareDist)
compareDist = currDist;
MA(looper,:) = currPoint;
end
end
end
Any help is appreciated. Thanks.
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per isakson
per isakson am 31 Okt. 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 am 31 Okt. 2014
How long does it take and how many times do you have to run it?

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Antworten (1)

lvn
lvn am 31 Okt. 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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