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تسجيل مستخدم جديدA Characterization of Approximation Resistance
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A predicate f:{-1,1}^k -> {0,1} with rho(f) = frac{|f^{-1}(1)|}{2^k} is called {it approximation resistant} if given a near-satisfiable instance of CSP(f), it is computationally hard to find an assignment that satisfies at least rho(f)+Omega(1) fraction of the constraints. We present a complete characterization of approximation resistant predicates under the Unique Games Conjecture. We also present characterizations in the {it mixed} linear and semi-definite programming hierarchy and the Sherali-Adams linear programming hierarchy. In the former case, the characterization coincides with the one based on UGC. Each of the two characterizations is in terms of existence of a probability measure with certain symmetry properties on a natural convex polytope associated with the predicate.
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