Let @math be a 3CNF formula with n variables and m clauses. A simple nonconstructive argument shows that when m is sufficiently large compared to n, most 3CNF formulas are not satisfiable. It is an open question whether there is an efficient refutation algorithm that for most such formulas proves that they are not satisfiable. A possible approach to refute a formula @math is: first, translate it into a graph @math using a generic reduction from 3-SAT to max-IS, then bound the maximum independent set of @math using the Lovasz @math function. If the @math function returns a value @math , this is a certificate for the unsatisfiability of @math . We show that for random formulas with @math clauses, the above approach fails, i.e. the @math function is likely to return a value of m.
@cite_1: We investigate relations between average case complexity and the complexity of approximation. Our preliminary findings indicate that this is a research direction that leads to interesting insights. Under the assumption that refuting 3SAT is hard on average on a natural distribution, we derive hardness of approximation results for min bisection, dense k-subgraph, max bipartite clique and the 2-catalog segmentation problem. No NP-hardness of approximation results are currently known for these problems.
The algorithm considered in the current paper for refuting @math by computing @math was presented in @cite_1 . There is was shown that when @math , almost surely @math . Our current work overcomes a difficulty that prevented the approach of @cite_1 to show that @math , not even for formulas @math with a linear number of clauses. The difficulty was the existence of pairs of clauses that share two variables.