research(nightly): spectral-ivf — graph-Laplacian partitioned ANN

[ruvnet]

Summary

Adds nightly RuVector research for Spectral IVF (2026-07-20): graph-Laplacian partitioned approximate nearest-neighbour search using the Fiedler vector as a continuous relaxation of the minimum balanced graph cut.

• Working Rust PoC: crates/ruvector-spectral-ivf — pure Rust, zero unsafe, zero external deps, WASM-compatible
• ADR: docs/adr/ADR-272-spectral-ivf.md
• Research document: docs/research/nightly/2026-07-20-spectral-ivf/README.md
• Real benchmark results: measured on Linux x86_64, Rust 1.94.1
• Public gist: docs/research/nightly/2026-07-20-spectral-ivf/gist.md

What this implements

Three IVF variants under a shared AnnIndex trait:

Variant	Partitioner	Build(ms)	Mean(µs)	Recall@10	Mem(KB)
KMeansIvf	Lloyd's k-means (baseline)	0	18.3	0.801	208.2
SpectralIvf	Fiedler bisection (cosine kNN)	90	31.3	1.000	208.2
CoherenceSpectralIvf	Fiedler bisection (cosine² kNN)	92	30.9	0.990	208.2

n=800, dim=64, 8 partitions, nprobe=4, 200 queries. All numbers from cargo run --release -p ruvector-spectral-ivf --bin benchmark.

Key finding: Spectral IVF achieves +20 percentage points better recall than k-means at identical memory cost and equal nprobe, by drawing partition boundaries along graph mincuts rather than Euclidean Voronoi cells.

Ecosystem connections

• ruvector-mincut: Fiedler vector = mincut relaxation (Cheeger inequality)
• ruvector-coherence: coherence-weighted edges in CoherenceSpectralIvf
• ruvector-graph: kNN graph is a subgraph of the RuVector graph store
• ruvector-diskann: partitions map to SSD pages
• ruvector-spann: complementary (SPANN spills; Spectral avoids wrong assignments at construction)
• ruvector-capgated: per-partition capability gates
• MCP memory tools: partition-scoped agent memory namespaces
• WASM: zero unsafe, no OS calls in search path

Test status

test result: ok. 15 passed; 0 failed; 0 ignored

Acceptance

[PASS] KMeansIvf: recall@10=0.801 (threshold ≥ 0.60)
[PASS] SpectralIvf: recall@10=1.000 (threshold ≥ 0.60)
[PASS] CoherenceSpectralIvf: recall@10=0.990 (threshold ≥ 0.60)
✓ All variants pass recall acceptance threshold.

Research doc

docs/research/nightly/2026-07-20-spectral-ivf/README.md

ADR

docs/adr/ADR-272-spectral-ivf.md

Crate

crates/ruvector-spectral-ivf

Benchmark command

cargo run --release -p ruvector-spectral-ivf --bin benchmark

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Generated by Claude Code