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Questions about Turing machines, a theoretical model of mechanical computation capable of simulating any computer program.

5 votes
Accepted

Any reason why Turing Machine would prevail on recursion theory?

With Turing machines you can talk about computer concepts such as running time and space usage. This is harder with $\mu$-recursive functions.
Bjørn Kjos-Hanssen's user avatar
-1 votes

Is there a complexity metric for finite state machines?

You could take the three-dimensional vector (states, transitions, symbols) as your measure of complexity. Disadvantage: you get incomparable levels of complexity. Advantage: you retain all the infor …
Bjørn Kjos-Hanssen's user avatar
2 votes

Why do we use $\Gamma$ to denote a TM's tape alphabet?

Following up on @PartialOrder's comment, while $\Gamma$ is not used in Chomsky & Schutzenberger or in Chomsky's 1962/1963 papers on PDAs, it is used in Ginsburg and Greibach 1966 as follows: A pus …
Bjørn Kjos-Hanssen's user avatar
1 vote

Complexity of the language of all TMs $M$ such that $L(M)$ is decidable

This set is not r.e. nor co-r.e., in fact it's complete at the 3rd level of the arithmetic hierarchy ($\Sigma^0_3$-complete). This is shown in Soare's textbook.
Bjørn Kjos-Hanssen's user avatar
0 votes

Problems understanding proof of smn theorem using Church-Turing thesis

So $g$ is a function such that $\Phi_{g(x)}(y)=f(x,y)$. All this means is that $g$ on input $x$ will output (print on its tape, if you will) a program $P$ that does the following: Code for $g(x)$: …
Bjørn Kjos-Hanssen's user avatar