PPT-1 Undecidability

Reading Chapter 8 amp 9 2 Decidability vs Undecidability There are two types of TMs based on halting Recursive TMs that always halt no matter accepting or nonaccepting . In the case of deterministic 64257nite au tomata problems like equivalence can be solved even in polynomial time Also there are e64259cient parsing algorithms for context free grammars If necessary we may brie64258y review some material on regular a Physics 1985 Physical processes are viewed as computations, and the difficulty of answering questions about them is characterized in On one hand, theoretical models describe physical processes by c Today •We’ve seen several undecidability proofs. •Today we’ll extract some of the key ideas of those •Two main ideas: –A formal definition of –Rice’s Theorem Date:May28,2012;typoscorrectedJune25,2014;referencetopublishedversionaddedOctober25,2014.2010MathematicsSubjectClassication.Primary03D35;Secondary00A05.Keywordsandphrases.Undecidability,decisionprobl 200 C Moore ............................... ................................. (4 rYm ................................. Figure 1. (n) The Smale horseshoe. (6) The Smale horseshoe, abbreviated as a map York University. COSC 4111. Lecture. . 4. 4111 Computability. Different Models. Reductions. Simple Reductions. Rice's Theorem. Acceptable. Acceptability Complete. Reductions to the Halting Problem. The Post Correspondence Prob. 2. Decidability vs. Undecidability. There are two types of TMs (based on halting):. (. Recursive. ) . . TMs that . always. halt. , no matter accepting or non-accepting .  . DECIDABLE. PROBLEMS.