MATLAB: Optimize inefficient piece of code

code optimizationMATLAB

Hi,
I have a piece of code as part of a bigger piece that is inefficient. The code is called many times and is a bottleneck in the proces also according to the matlab profiler. I feel it can be done faster. The code looks as follows
 clear all
 % initialize variables of interest
 l1=rand(1,10);
 l2=rand(1,10);
 p1=rand(3,10);
 p2=rand(3,10);
 % start inefficient code
 [c,ind]=min([l1;l2]);
 r(:,:,1)=p1;
 r(:,:,2)=p2;
 for it=1:10
     p3(:,it)=r(:,it,ind(it));
 end
I would like to do the for loop in one go (so remove the for loop). l1 and l2 are distances (l1 is norm of p1 and l2 is norm of p2), and p1, p2 are 3d coordinates. The goal of the code is to pick the coordinates of p1, p2 from the one with the smallest distance.

Best Answer

Hi!
You can of course avoid the loop with
p3(1:3, ind==1) = p1(:, ind==1);
p3(1:3, ind==2) = p2(:, ind==2);
This avoids the r-lines before the loop as well. Use '~' instead of 'c' if you are not interessted in the value of the 'min' call.
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