Hi,
you can do it using one for loop, e.g.
n = 82000;
A = rand(n,2);
nb = zeros(n,1);
dist = 0.1^2;
tic
for i=1:n-1
tmp = sum(power(bsxfun(@minus,A,A(i,:)),2),2);
nb(i) = sum(tmp < dist)-1;
end
toc
This needs approx. 94 seconds on my machine.
One can also parallelize that code pretty good (requieres Parallel Computing Toolbox), e.g.
pool = parpool(4);
tic
spmd
for i=labindex:numlabs:n-1
tmp = sum(power(bsxfun(@minus,A,A(i,:)),2),2);
nb(i) = sum(tmp < dist)-1;
end
end
toc
delete(pool)
Which needs approx. 67 seconds on my machine (not taking the worker startup/shutdown time into account). When you need to deal with more points to check the speedup should be even better.
