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Is it possible to simulate a stack-based machine using a 1-tape turing machine? I cannot wrap my head around it as turing machines do not provide mechanisms such as pointers.

I failed to find any examples or explanations. If it is possible, how?

Raphael
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just.kidding
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2 Answers2

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Machines that have only a stack are called pushdown automata. They are less powerful than Turing machine, so yes: TMs can simulate stacks.

Turing machines are a fairly simplistic model of computation, which can make programming in them hard. Try to start with simple things; for instance, implement a counter. If you feel ambitious, try implementing the basic building blocks of (Turing-complete) imperative programming as Turing machines. This should convince you, then, that TMs are as powerful as any other¹ model.

As for your question, you don't need pointers for a stack. TM tapes have a direction, and you can easily label cells by introducing special alphabet symbols; the TM can then move over the tape and look for these labels. It's all a matter of encoding.

  1. Ignoring hyper-computation.
Raphael
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In addition to what @Raphael said, it's very easy to actually do it. Just make a rule for your Turing Machine that every time it moves left, it will also write null. Voilà! You have made a Pushdown Automata.

Ben I.
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  • Thank you for your answer. I actually need to design a simulation for a machine supporting both a stack and registers. – just.kidding Apr 25 '17 at 19:03
  • @just.kidding Building a simulator for "modern" machine architectures is definitely possible, but not very interesting (by my estimation). – Raphael Apr 25 '17 at 20:28