{"title":"The density and complexity of polynomial cores for intractable sets","authors":"Pekka Orponen, Uwe Schöning","doi":"10.1016/S0019-9958(86)80024-9","DOIUrl":null,"url":null,"abstract":"<div><p>Let <em>A</em> be a recursive problem not in <em>P</em>. Lynch has shown that <em>A</em> then has an infinite recursive <em>polynomial complexity core</em>. This is a collection <em>C</em> of instances of <em>A</em> such that every algorithm deciding <em>A</em> needs more than polynomial time almost everywhere on <em>C</em>. We investigate the complexity of recognizing the instances in such a core, and show that every recursive problem <em>A</em> not in <em>P</em> has an infinite core recognizable in subexponential time. We further study how dense the core sets for <em>A</em> can be, under various assumptions about the structure of <em>A</em>. Our main results in this direction are that if <em>P</em> ≠ <em>NP</em>, then <em>NP</em>-complete problems have polynomially nonsparse cores recognizable in subexponential time, and that EXPTIME-complete problems have cores of exponential density recognizable in exponential time.</p></div>","PeriodicalId":38164,"journal":{"name":"信息与控制","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"1986-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0019-9958(86)80024-9","citationCount":"46","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"信息与控制","FirstCategoryId":"1093","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0019995886800249","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q4","JCRName":"Mathematics","Score":null,"Total":0}
引用次数: 46
Abstract
Let A be a recursive problem not in P. Lynch has shown that A then has an infinite recursive polynomial complexity core. This is a collection C of instances of A such that every algorithm deciding A needs more than polynomial time almost everywhere on C. We investigate the complexity of recognizing the instances in such a core, and show that every recursive problem A not in P has an infinite core recognizable in subexponential time. We further study how dense the core sets for A can be, under various assumptions about the structure of A. Our main results in this direction are that if P ≠ NP, then NP-complete problems have polynomially nonsparse cores recognizable in subexponential time, and that EXPTIME-complete problems have cores of exponential density recognizable in exponential time.