# How to make a nested FOR loop of distance between points?

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Nicole Konforti il 22 Mar 2017
Commentato: Iddo Weiner il 22 Mar 2017
I have two sets each with ten objects with coordinates (x,y,z) in each set. I want to map the distances between each of the points in set 1 to each of the points in set 2. At the end, I want an array 1x100, with the 100 unique distances between each ten points of set 1 and each ten points of set 2.
To do this, I was thinking of having a code similar to this:
for I = 1:1 xvalue1 = rand(10,1)*1000; end
for J = 1:1 yvalue1 = rand(10,1)*1000; end
for K = 1:1 zvalue1 = rand(10,1)*1000; end
set1 = [xvalue1 yvalue1 zvalue1];
for I = 1:1 xvalue2 = rand(10,1)*1000; end
for J = 1:1 yvalue2 = rand(10,1)*1000; end
for K = 1:1 zvalue2 = rand(10,1)*1000; end
set2 = [xvalue2 yvalue2 zvalue2];
Which runs well. For the calculating the actual distances, my preliminary code is:
i = 1;
j = 1;
for i=1:10
distance(i) = sqrt((xvalue2(i+1) - xvalue1(i+1)).^2 + (yvalue2(i+1) - yvalue1(i+1)).^2 + (zvalue2(i+1) - zvalue1(i+1)).^2);
for j=1:10
distance(j) = sqrt((xvalue2(j+1) - xvalue1(j+1)).^2 + (yvalue2(j+1) - yvalue1(j+1)).^2 + (zvalue2(j+1) - zvalue1(j+1)).^2);
end
end
However, the error I get is that "the index exceeds matrix dimensions" Does anyone understand where my error is?
Thank you
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### Risposta accettata

Iddo Weiner il 22 Mar 2017
Hi, you had some unnecessary bits of code there that made it complicated to follow. Here's a shorter code that does what you asked for:
% get random data
set1 = rand(10,3)*1000 ;
set2 = rand(10,3)*1000 ;
% calculate
OUT = nan(10,10); %create array for holding output
for i = 1:(length(set1))
for j = 1:length(set2)
OUT(i,j) = sum( (set1(i,:) - set2(j,:)).^2);
end
end
% plot
imagesc(OUT)
ylabel('set1')
xlabel('set2')
HC = colorbar;
ylabel(HC,'distance')
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Iddo Weiner il 22 Mar 2017
BTW - your error is a result using i+1. i runs until 10, so in the last iteration your i equals 11, which doesn't exist in the sets

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