(1+ε)-approximate nearest neighbor search

(1+ε)-approximate nearest neighbor search is a variant of the nearest neighbor search problem. A solution to the (1+ε)-approximate nearest neighbor search is a point or multiple points within distance (1+ε) R from a query point, where R is the distance between the query point and its true nearest neighbor.^[1]

Reasons to approximate nearest neighbor search include the space and time costs of exact solutions in high-dimensional spaces (see curse of dimensionality) and that in some domains, finding an approximate nearest neighbor is an acceptable solution.

Approaches for solving (1+ε)-approximate nearest neighbor search include k-d trees,^[2] locality-sensitive hashing and brute-force search.