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Learning a SAT Solver from Single-Bit Supervision

Paper · 2018 · Daniel Selsam, Matthew Lamm, Benedikt Bünz et al.

Summary

Selsam et al. ask whether a neural network can learn to solve propositional satisfiability (SAT), an NP-complete problem, when it is told only whether each instance is satisfiable. They build NeuroSAT, a message passing neural network (MPNN). It represents a CNF formula as a graph of literal and clause nodes and updates their embeddings with layer-norm LSTMs. The design respects the symmetries of SAT: reordering variables, clauses or literals, or flipping the sign of a variable, cannot change its output. Training uses the SR(n) generator, which produces pairs of random problems: one satisfiable and one unsatisfiable, differing in a single literal. On satisfiable inputs the network shows a sudden phase transition to confident "sat" votes, and a satisfying assignment can usually be read from its activations. This makes NeuroSAT an end-to-end solver. Running more iterations lets it solve larger, harder problems than those seen in training, and it transfers to other encoded problems. It is still far weaker than conventional solvers. The work matters because it suggests neural networks can learn genuine search procedures from minimal supervision.

Key points

  • Supervision: each training example gives only one bit, satisfiable or not. Labels come from an existing SAT solver run on SR(n) instances.
  • SR(n) generator: clause sizes are sampled with a mean slightly above 4. This blocks shortcuts based on crude statistics, because paired sat/unsat problems differ by negating a single literal occurrence.
  • Architecture:
    • Learned initial vectors L_init and C_init.
    • Three MLPs: L_msg, C_msg and L_vote.
    • Two layer-norm LSTMs: L_u and C_u.
    • A Flip operator that exchanges messages between complementary literals.
    • The prediction is the mean of per-literal votes, trained with sigmoid cross-entropy.
    • No parameter depends on problem size.
  • Iterations: training uses a few dozen message-passing rounds, while at test time the model keeps finding solutions after hundreds or thousands of rounds.
  • Generalization and NeuroUNSAT: trained only on random SAT, NeuroSAT solves small random-graph instances of four other encoded problems: coloring a graph, finding a clique, finding a dominating set and finding a vertex cover. A variant trained on different data, NeuroUNSAT, instead pinpoints the variables of small contradictions, which can speed up building resolution proofs.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

 Fields, topics and concepts

Cite

Cite as Daniel Selsam, Matthew Lamm, Benedikt Bünz, Percy Liang, Leonardo de Moura and David L. Dill. 2018. Learning a SAT Solver from Single-Bit Supervision. arXiv:1802.03685.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.48550/arxiv.1802.03685 · arXiv 1802.03685

@misc{selsam2018learning,
  title = {{Learning a SAT Solver from Single-Bit Supervision}},
  author = {Daniel Selsam, Matthew Lamm, Benedikt Bünz, Percy Liang, Leonardo {de Moura} and David L. Dill},
  year = {2018},
  doi = {10.48550/arxiv.1802.03685},
  eprint = {1802.03685},
  archivePrefix = {arXiv},
  url = {https://doi.org/10.48550/arxiv.1802.03685}
}

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