0-4-2-understand-approximate-nearest-neighbor

name	0.4.2-understand-approximate_nearest_neighbor
description	[0.4.2] An ANN algorithm that trades exact recall for sub-linear query time by probabilistically organizing the embedd

understand-approximate_nearest_neighbor

CALL NUMBER: vector_databases_and_embeddings.approximate_nearest_neighbor DEFINITION: An ANN algorithm that trades exact recall for sub-linear query time by probabilistically organizing the embedding space into clusters or graphs.

Invoke this skill to understand approximate_nearest_neighbor down to its primitives. The RELATIVE ROOT below is the least-fixed-point closure of everything it bundles from — the full import cone, grouped by the lib each prim comes from. Projected from a prover-typed KB (MAP/SWI-Prolog consistency gate): every reference below resolves.

THE RELATIVE ROOT (the import cone, by lib)

from vector_databases_and_embeddings

• faiss (d1): Meta's open-source C++/Python library for dense vector similarity search; implements IVF, PQ, HNSW, ONNG, and GPU-accelerated kernels with optional 8-bit quantization.
• hnsw_index (d1): Hierarchical Navigable Small World graph; layered skip-list + NN graph enabling logarithmic-layer traversal then constant-time local search.
• ivf_index (d1): Inverted File Index; clusters vectors into Voronoi cells via k-means; search prunes to nearest centroids then scans partitions.
• product_quantization (d2): A vector quantization technique that splits a high-dimensional vector into subvectors, independently quantizes each subvector, and concatenates codes to form a compact representation.
• scalar_quantization (d2): Floating-point values mapped to low-precision (e.g. int8); reduces memory 4x with modest accuracy loss.
• indexing_strategy (d2): Choice and configuration of ANN algorithm (HNSW, IVF, ANNOY, LSH) and its parameters (ef, nlist, nprobe) governing recall/speed trade-off.
• memory_footprint (d3): RAM or VRAM required to hold index and vectors; quantization (PQ, int8) is the primary compression lever.

CONSUMERS (what needs this)

ann_benchmark, approximate_query, idx_query_latency_budget, idx_recall_target, nearest_neighbor_search, recall_at_k

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Projected from the vector databases and embeddings KB (262 concepts / 150 relations) — consistency-typed by MAP; the facet list after the colon IS the cross-lib dependency web.

(leaf — this is an actual skill.)