A neural network catalyzer for multi-dimensional similarity search

This paper aims at learning a function mapping input vectors to an output space in a way that improves high-dimensional similarity search. As a proxy objective, we design and train a neural network that favors uniformity in the spherical output space, while preserving the neighborhood structure after the mapping. For this purpose, we propose a new regularizer derived from the Kozachenko-Leonenko differential entropy estimator and combine it with a locality-aware triplet loss. Our method operates as a catalyzer for traditional indexing methods such as locality sensitive hashing or iterative quantization, boosting the overall recall. Additionally, the network output distribution makes it possible to leverage structured quantizers with efficient algebraic encoding, in particular spherical lattice quantizers such as the Gosset lattice E8. Our experiments show that this approach is competitive with state-of-the-art methods such as optimized product quantization.