No Better Ways to Generate Hard NP Instances than Picking Uniformly at Random
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AUTHOR NAME
Leonid A. Levint
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AUTHOR AFFIL
Computer Science department; Boston University
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AUTHOR ADDR
111 Cummington St. Boston
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ABSTRACT
Distributed NP (DNP) problems are ones supplied with probability distributions of in-stances. We can consider their hardness for typical instances rather than just for the worst case (which may be extremely rare). Reductions between such problems must ap-proximately preserve the distributions. A number of papers show completeness of sev-eral natural DNP problems in the class of aJl DNP problems with P-time computable distributions. This approach has been criti-cized as too restrictive: hard instances may be generated with samplable but not com-putable in P-time distributions. There were doubts whether naturul problems (which all have simple distributions) may be complete for the class of all NP problems with sam-plable distributions. We show that every DNP problem com-plete for P-time computable distributions is also complete for all samplable distributions. This rather surprising observation makes the concept of average case NP completeness ro-