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Questions tagged [turing-machines]

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

The classic paper that started it all.

On Computable Numbers, with an application to the Entscheidungsproblem

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why don't we use machines with random access memory as our basic model of computation?

Turing machines are perhaps the most popular model of computation for theoretical computer science. Turing machines don't have random access memory, since we can only do a read where the slider is currently located. This seem unwieldy to me. Why…
user56834
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Practical importance of Turing machines?

I am an electrical engineer, and only had one CS course in college 26 years ago. However, I am also a devoted Mathematica user. I have the sense that Turing Machines are very important in computer science. Is the importance only in the theory of…
Ted Ersek
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Can input to a Turing machine be of infinite length?

Considering only the alphabet $\Sigma = \{0,1\}$, the strings which can be given as input to the Turing machines are from the set $\Sigma^{*}$. But does it make sense for the input to be an infinite binary string ? For example if a Turing machine…
advocateofnone
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Why is the blank symbol not considered part of the input alphabet of a Turing machine?

Definitions of Turing machines are always explicit about the blank symbol not being part of the input alphabet. I wonder what goes wrong when you would make it part of the input alphabet, because effectively the blank symbol already seems to be part…
Confusion
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Turing machine - infinite tape in one or two directions

I have seen turing machines beeing represented with tapes infinite in one, and in two directions. Is there any difference in the power of such turing machines, or are they basically equivalent? In my head I think they are equivalent, since I guess…
user2795095
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How can a Turing machine compare two strings without modifying them?

In Sipser's Introduction to the Theory of Computation, the author explains that two strings can be compared by “zigzagging” back and forth between them and “crossing off” one symbol at a time (i.e., replacing them with a symbol such as $x$). This…
Frank
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Difference between Turing machine and Universal Turing machine

I've read what a Turing machine and a UTM are, but I don't get the difference. What can a UTM do which a normal Turing machine can not?
Moltimor
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Do real world computers use the Turing Machine mechanism?

I am a high school student in the twelfth grade. I study high-level programming, and a little bit of basic computer science. I have recently started to understand what a Turing Machine is. I wanted to ask: I understand that a Turing Machine is a…
Aviv Cohn
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How many Turing machines are there with $c$ characters and $n$ states?

By $c$ character I mean the numbers $0,\dots,c-1$ and the blank symbol $b$, and by $n$ states I mean $n$ non-accepting states, reject and accept. We can assume every $n$-state Turing machine has $(c+1)n$ transitions going to either another…
ruler501
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The first Turing machine

Does anyone know how efficient was the first Turing machine that Alan Turing made? I mean how many moves did it do per second or so... I'm just curious. Also couldn't find any info about it on the web.
McLovin
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How to find left-hand side of tape on a Turing Machine?

I am pretty new to Turing Machines and am trying to figure something out. So let's say I have a tape with input 0 0 1 0 0 1 The language is twice as many 0's than 1's. So first time through, I will mark an X on the first 1 I find. Then when I am…
bob afro
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How to construct and write down a Turing machine for a given language?

In my class we just started learning about Turing machines. I think I understand the concept but am unsure how to syntactically solve any problem related to one. I am presented with the problem: Build a Turing machine accepting $(b + c)^+$$\#a^+$…
Matt Hintzke
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Whats the difference between an oracle and a decider in Computational Theory?

I'm learning about Turing reductions at the moment and I'm just wondering is there any difference between an oracle and a decider, As they seemingly do the exact same thing. I understand the point of a oracle is that we don't have to know how it…
ItsYourBoi
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Can the mind be a finite automata and still invent the Turing machine?

The Turing machine was invented by a human mind. Presumably, nothing less powerful than a Turing machine can invent a Turing machine. However, a Turing machine has infinite tape, whereas the mind is situated in a finite universe, and thus can…
yters
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Why is it that every k-tape Turing machine has a 1-tape TM that runs in $O(t^2(n))$?

Apparently, for every k-tape Turing machine that runs in time $O(t(n))$, there exists a 1-tape Turing machine that runs in $O(t^2(n))$. I can see how any multi-tape machine $M$ can be simulated by a 1-tape machine $S$. Just have the tape of $S$…
David Faux
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