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A '''Multitrack [[Turing machine]]''' is a specific type of [[Multi-tape Turing machine]]. In a standard n-tape Turing machine, n heads move independently along n tracks. In a n-track Turing machine, one head reads and writes on all tracks simultaneously. A tape position in a n-track Turing Machine contains n symbols from the tape alphabet. It is equivalent to the standard Turing machine and therefore accepts precisely the recursively enumerable languages. | |||
== Formal definition == | |||
A multitape Turing machine can be formally defined as a 6-tuple <math>M= \langle Q, \Sigma, \Gamma, \delta, q_0, F \rangle </math>, where | |||
* <math>Q</math> is a finite set of states | |||
* <math>\Sigma</math> is a finite set of symbols called the ''tape alphabet'' | |||
*<math>\Gamma \in Q</math> | |||
* <math>q_0 \in Q</math> is the ''initial state'' | |||
* <math>F \subseteq Q</math> is the set of ''final'' or ''accepting states''. | |||
*<math>\delta \subseteq \left(Q \backslash A \times \Sigma\right) \times \left( Q \times \Sigma \times d \right)</math> is a relation on states and symbols called the ''transition relation''. | |||
*<math>\delta \left(Q_i,[x_1,x_2...x_n]\right)=(Q_j,[y_1,y_2...y_n],d)</math> | |||
where <math>d \in {L,R}</math> | |||
== Proof of equivalency to standard Turing machine== | |||
This will prove that a two-track Turing machine is equivalent to a standard Turing machine. This can be generalized to a n-track Turing machine. Let L be a recursively enumerable language. Let M= <math>\langle Q, \Sigma, \Gamma, \delta, q_0, F \rangle </math> be standard Turing machine that accepts L. Let M' is a two-track Turing machine. To prove M=M' it must be shown that M <math> \subseteq </math> M' and M' <math> \subseteq </math> M | |||
*<math> M \subseteq M' </math> | |||
If all but the first track is ignored then M and M' are clearly equivalent. | |||
*<math> M' \subseteq M </math> | |||
The tape alphabet of a one-track Turing machine equivalent to a two-track Turing machine consists of an ordered pair. The input symbol a of a Turing machine M' can be identified as an ordered pair [x,y] of Turing machine M. The one-track Turing machine is: | |||
M= <math>\langle Q, \Sigma \times {B}, \Gamma \times \Gamma, \delta ', q_0, F \rangle </math> with the transition function <math>\delta \left(q_i,[x_1,x_2]\right)=\delta ' \left(q_i,[x_1,x_2]\right)</math> | |||
This machine also accepts L. | |||
== References == | |||
Thomas A. Sudkamp (2006). Languages and Machines, Third edition. Adison Wesley. ISBN 0-321-32221-5. Chapter 8.6: Multitape Machines: pp 269-271 | |||
[[Category:Turing machine]] |
Latest revision as of 11:05, 12 December 2013
Template:Turing A Multitrack Turing machine is a specific type of Multi-tape Turing machine. In a standard n-tape Turing machine, n heads move independently along n tracks. In a n-track Turing machine, one head reads and writes on all tracks simultaneously. A tape position in a n-track Turing Machine contains n symbols from the tape alphabet. It is equivalent to the standard Turing machine and therefore accepts precisely the recursively enumerable languages.
Formal definition
A multitape Turing machine can be formally defined as a 6-tuple , where
- is a finite set of states
- is a finite set of symbols called the tape alphabet
- is the initial state
- is the set of final or accepting states.
- is a relation on states and symbols called the transition relation.
Proof of equivalency to standard Turing machine
This will prove that a two-track Turing machine is equivalent to a standard Turing machine. This can be generalized to a n-track Turing machine. Let L be a recursively enumerable language. Let M= be standard Turing machine that accepts L. Let M' is a two-track Turing machine. To prove M=M' it must be shown that M M' and M' M
If all but the first track is ignored then M and M' are clearly equivalent.
The tape alphabet of a one-track Turing machine equivalent to a two-track Turing machine consists of an ordered pair. The input symbol a of a Turing machine M' can be identified as an ordered pair [x,y] of Turing machine M. The one-track Turing machine is:
M= with the transition function
This machine also accepts L.
References
Thomas A. Sudkamp (2006). Languages and Machines, Third edition. Adison Wesley. ISBN 0-321-32221-5. Chapter 8.6: Multitape Machines: pp 269-271