A Heterogeneous High-Dimensional Approximate Nearest Neighbor Algorithm

We consider the problem of finding high-dimensional approximate nearest neighbors. We introduce an old style probabilistic formulation instead of the more general locality sensitive hashing (LSH) formulation, and show that at least for sparse problems it recognizes much more efficient algorithms than the sparseness destroying LSH random projections. Efficient algorithms for homogeneous (all coordinates have the same probability distribution) problems are well known, the most famous reference being the work by Broder in 1998. The main theme of this paper is to find its “best” generalization to heterogeneous (different coordinate probabilities) problems. We find a practical algorithm which is asymptotically best in a wide natural class of algorithms. Readers interested in the more complicated very best (at least up to date) can look up our previous work in 2010. The analysis of our algorithms reveals that its complexity is governed by an information like function, which we call “small leaves bucketing forest information.” Any doubts whether it is “information” are dispelled by the aforementioned work.