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Approximate Nearest Neighbors in Limited Space
Proceedings of the 31st Conference On Learning Theory, PMLR 75:2012-2036, 2018.
Abstract
We consider the (1+ϵ)-approximate nearest neighbor search problem: given a set X of n points in a d-dimensional space, build a data structure that, given any query point y, finds a point x∈X whose distance to y is at most (1+ϵ)min for an accuracy parameter \epsilon \in (0,1). Our main result is a data structure that occupies only O(\epsilon^{-2} n \log(n) \log(1/\epsilon)) bits of space, assuming all point coordinates are integers in the range \{-n^{O(1)} \ldots n^{O(1)}\}, i.e., the coordinates have O(\log n) bits of precision. This improves over the best previously known space bound of O(\epsilon^{-2} n \log(n)^2), obtained via the randomized dimensionality reduction method of Johnson and Lindenstrauss (1984). We also consider the more general problem of estimating all distances from a collection of query points to all data points X, and provide almost tight upper and lower bounds for the space complexity of this problem.