<p><a href="http://arxiv.org/abs/0804.1448" rel="nofollow">Fast k Nearest Neighbor Search using GPU</a></p>

<p>I haven't tested, used it, nothing. I just googled and posted the first link I found.</p>
Best GPU algorithm for calculating lists of neighbours
<p>Given a collection of thousands of points in 3D, I need to get the list of neighbours for each particle that fall inside some cutoff value (in terms of euclidean distance), and if possible, sorted from nearest fo farthest. </p>

<p>Which is the fastest GPU algorithm for this purpose in the CUDA or OpenCL languages? </p>