Subtractive Mixture Models: Representation and Learning
summary
Introduces subtractive mixtures by allowing negative mixture weights, then enforces non-negativity by squaring the circuit, producing squared nonmonotonic circuits that expand K components to O(K^2) via cross-terms; partition functions remain tractable when circuits are structured decomposable so renormalization is feasible and GPU-friendly via layerwise tensor/Kronecker operations. Proves an exponential separation (lower bound) versus monotonic PCs, shows empirical log‑likelihood gains on real datasets (including GPT-2 token distributions with large vocabularies), implements sampling by autoregressive inverse‑transform, and flags latent‑variable semantics and structure learning as open issues.
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chapters (14)
- 0:00Subtractive mixture models intro
- 3:18Mixture models overview
- 10:10Subtractive models with negatives
- 14:49Squaring circuits for non-negativity
- 19:30Deep structured circuits squaring
- 23:09Tensorized circuits for GPU
- 30:11Connections to kernels and networks
- 34:11Inference with nonmonotonic circuits
- 36:45Expressivity gains from squaring
- 38:30Lower bounds for subtractive models
- 40:41Empirical evaluation
- 46:21Open problems
- 48:08Summary
- 49:16Q&A
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