Partitioned K-nearest Neighbor Local Depth For Scalable Comparison-based Learning | Awesome Similarity Search Papers

Partitioned K-nearest Neighbor Local Depth For Scalable Comparison-based Learning

A triplet comparison oracle on a set (S) takes an object (x \in S) and for any pair (\{y, z\} \subset S \setminus \{x\}) declares which of (y) and (z) is more similar to (x). Partitioned Local Depth (PaLD) supplies a principled non-parametric partitioning of (S) under such triplet comparisons but needs (O(n^2 log{n})) oracle calls and (O(n^3)) post-processing steps. We introduce Partitioned Nearest Neighbors Local Depth (PaNNLD), a computationally tractable variant of PaLD leveraging the (K)-nearest neighbors digraph on (S). PaNNLD needs only (O(n K log{n})) oracle calls, by replacing an oracle call by a coin flip when neither (y) nor (z) is adjacent to (x) in the undirected version of the (K)-nearest neighbors digraph. By averaging over randomizations, PaNNLD subsequently requires (at best) only (O(n K^2)) post-processing steps. Concentration of measure shows that the probability of randomization-induced error (\delta) in PaNNLD is no more than (2 e^{-\delta^2 K^2}).

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