The threshold for SDP-refutation of random regular NAE-3SAT
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Unlike its cousin 3SAT, the NAE-3SAT (not-all-equal-3SAT) problem has the property that spectral/SDP algorithms can efficiently refute random instances when the constraint density is a large constant (with high probability). But do these methods work immediately above the "satisfiability threshold", or is there still a range of constraint densities for which random NAE-3SAT instances are unsatisfiable but hard to refute? We show that the latter situation prevails, at least in the context of random regular instances and SDP-based refutation. More precisely, whereas a random d-regular instance of NAE-3SAT is easily shown to be unsatisfiable (whp) once d ≥ 8, we establish the following sharp threshold result regarding efficient refutation: If d < 13.5 then the basic SDP, even augmented with triangle inequalities, fails to refute satisfiability (whp), if d > 13.5 then even the most basic spectral algorithm refutes satisfiability (whp).
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