ComputingStructure in Approximation Classes ?
نویسندگان
چکیده
The study of the approximability properties of NP-hard optimization problems has recently made great advances mainly due to the results obtained in the eld of proof checking. The last important breakthrough shows the APX-completeness of several important optimization problems is proved and thus reconciles`two distinct views of approximation classes: syntactic and computational'. In this paper we obtain new results on the structure of several computationally-deened approximation classes. In particular, after deening a new approximation preserving reducibility to be used for as many approximation classes as possible, we give the rst examples of natural NPO-complete problems and the rst examples of natural APX-intermediate problems. Moreover, we state new connections between the approximability properties and the query complexity of NPO problems.
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