How to vectorise or speedup the code

Question

Eugene Pashinov 2020-2-16

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评论： darova 2020-2-16

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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Answer 1

darova 2020-2-16

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在 MATLAB Online 中打开

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