# How to vectorise or speedup the code

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Eugene Pashinov on 16 Feb 2020
Commented: darova on 16 Feb 2020
Hello. I have Lat(2689x1) Lon(2689x1) arrays that coordinaines coordinates of meteostations, and lat (1200x200) lon (1200x200) arrays with coordinates of satellite's measurements M(1200x200). I need to find elements of satelletes measurements, that located closer then 0.25 deg to meteostations. What i've did:
k=1;
for m=1:length(Lat)
x=lat-Lat(m);
y=lon-Lon(m);
[a,b]=find(abs((x))<=0.25 & abs((y))<=0.25);
for n=1:length(a)
Mes(k,n)=M(a(n),b(n))
end
St_N(k)=m;
k=k+1;
end;
Because of many loops it works very long. Is there any way to vectorise or speedup this code?
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### Accepted Answer

darova on 16 Feb 2020
Try pdist2
D = pdist2([Lat(:) Lon(:)],[lat(:) lon(:)]); % create every possible combinations of distances
[i,j] = find(D<=0.25); % find every distance satisfies condition
% i - station of (Lat,Lon)
% j - station of (lat,lon)
[i1,j1] = ind2sub(j,size(lat)); % return to 2D matrix
Mes = M(i1,j1); % stations that close enough
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darova on 16 Feb 2020
Don't use ind2sub. It's not correct in this case
% [i1,j1] = ind2sub(j,size(lat)); % return to 2D matrix
Just one index
Mes = M(j); % stations that close enough

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