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| Content Provider | ACM Digital Library |
|---|---|
| Author | Raghavendra, Prasad Rao, Satish Schramm, Tselil |
| Abstract | Random constraint satisfaction problems (CSPs) are known to exhibit threshold phenomena: given a uniformly random instance of a CSP with n variables and m clauses, there is a value of m = Ω(n) beyond which the CSP will be unsatisfiable with high probability. Strong refutation is the problem of certifying that no variable assignment satisfies more than a constant fraction of clauses; this is the natural algorithmic problem in the unsatisfiable regime (when m/n = Ï (1)). Intuitively, strong refutation should become easier as the clause density m/n grows, because the contradictions introduced by the random clauses become more locally apparent. For CSPs such as k-SAT and k-XOR, there is a long-standing gap between the clause density at which efficient strong refutation algorithms are known, m/n â ¥ à (nk/2â 1), and the clause density at which instances become unsatisfiable with high probability, m/n = Ï (1). In this paper, we give spectral and sum-of-squares algorithms for strongly refuting random k-XOR instances with clause density m/n â ¥ à (n(k/2â 1)(1â δ)) in time exp(à $(n^{δ}))$ or in à $(n^{δ})$ rounds of the sum-of-squares hierarchy, for any δ â [0,1) and any integer k â ¥ 3. Our algorithms provide a smooth transition between the clause density at which polynomial-time algorithms are known at δ = 0, and brute-force refutation at the satisfiability threshold when δ = 1. We also leverage our k-XOR results to obtain strong refutation algorithms for SAT (or any other Boolean CSP) at similar clause densities. Our algorithms match the known sum-of-squares lower bounds due to Grigoriev and Schonebeck, up to logarithmic factors. . |
| Starting Page | 121 |
| Ending Page | 131 |
| Page Count | 11 |
| File Format | |
| ISBN | 9781450345286 |
| DOI | 10.1145/3055399.3055417 |
| Language | English |
| Publisher | Association for Computing Machinery (ACM) |
| Publisher Date | 2017-06-19 |
| Publisher Place | New York |
| Access Restriction | Subscribed |
| Subject Keyword | Strong refutation Spectral algorithms Sum-of-squares hierarchy Random constraint satisfaction problems |
| Content Type | Text |
| Resource Type | Article |
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