CS2303 TOC 2 MARKS.pdf

# 20 what is off line turing machine an off line turing

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20. What is off-line Turing Machine? An Off-line Turing Machine is a multitape TM whose input tape is read only. The Turing Machine is not allowed to move the input tape head off the region between left and right end markers.

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III Year V Semester CSE CS2303 Theory of Computation Adhiparasakthi College of Engg., G.B. Nagar, Kalavai Page 18 of 20 UNIT V 1. What is the weak-form of Turing thesis? A Turing Machine can compute anything that can be computed by a general purpose digital computer. 2. What is the strong-form of Turing thesis? A Turing Machine can compute anything that can be computed. This is the strong form of Turing thesis. 3. When a language is said to be recursively enumerable? A language is recursively enumerable if there exists a Turing Machine that accepts every string of the language and does not accept strings that are not in the language. 4. When a language is said to be recursive? A language L is said to be recursive if there exists a Turing machine M that accepts L, and goes to halt state or else M rejects L. 5. What is diagonalization language? The language L d . Which consists of all those strings w such that the Turing machine represented by w does not accept the input w. L d = { w i | w i L(M i )} 6. Define decidability (or) decidable problems? A problem is said to be decidable if there exists a Turing machine which gives one ‘yes’ or ‘no’ answer for every input in the language. (or) A problem is said to be decidable if it is a recursive language. 7. Define Undecidable problem? If a problem is not a recursive language, then it is called undecidable problem. 8. Define Universal language? A Universal Turing Machine Mu is an automation, that given as input the description of any Turing Machine M and a string w, can simulate the computation of M on w. 9. What are the reasons for a TM not accepting its input? i) The TM may halt in a non final state. ii) The TM may enter into an indefinite loop. 10. Define trivial property? A property is trivial if it is either empty of is all RE languages. 11. Define rice Theorem? Every non-trivial property of the RE languages is undecidable.
III Year V Semester CSE CS2303 Theory of Computation Adhiparasakthi College of Engg., G.B. Nagar, Kalavai Page 19 of 20 12. Define post’s correspondence problem? An instance of PCP consists of two lists, A = w 1 , w 2 , w 3 , . . . . . . . w k B = x 1 , x 2 , x 3 , . . . . .. . . . .x k of strings over some ∑. This instance of PCP has a solution if there is any sequence of integers i 1 , i 2 ,, ………….i m with m≥1. Such that w i1 , w i2 , w i3 ………………………..w im = x i1 , x i2 , x i3 ,………….x im The sequence of i 1 ,i 2 ,……………..i m is a solution to this instance of PCP. 13. Let A and B be lists of three strings each, as defined in the following table?

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