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> You could even implement a linear bounded Turing machine as an FSM it would just take an ungodly number of states. To be clear, these things have formal defi
by frankmcsherry 9y ago
> You could even implement a linear bounded Turing machine as an FSM it would just take an ungodly number of states.
To be clear, these things have formal definitions, and this statement is not correct.
1. A linear bounded automaton[0] is a Turing machine that can only overwrite symbols presented on its input tape as input. However, the definition of the automaton is still required to be finite, but it is required to operate on unboundedly large input tapes.
2. A finite state machine[1] is a model of computation where the sequence of input symbols are observed once and the machine is at all times in one of a finite number of states. It is equivalent to a TM that can only move right (and consequently cannot read anything it writes to the tape).
They are different, formally[2]. There are languages that a LBA can accept that a FSM cannot accept (famously, the strings of balanced parentheses cannot be recognized by a FSM).
[0]: https://en.wikipedia.org/wiki/Linear_bounded_automaton https://en.wikipedia.org/wiki/Linear_bounded_automaton
[1]: https://en.wikipedia.org/wiki/Finite-state_machine https://en.wikipedia.org/wiki/Finite-state_machine
[2]: https://en.wikipedia.org/wiki/Pumping_lemma_for_regular_languages https://en.wikipedia.org/wiki/Pumping_lemma_for_regular_lang...
- setra 9y agoThis is correct from the unbound theoretical tape perspective. I should have expanded my point you are very correct. If you look in the context of physical realization (finite) a tape that can be written is some form of RAM. Beyond O(1) complexity all of these machines can express each other with different amounts of RAM. Even in the theoretical model an FSM can accept balanced parentheses of finite depth. My FSM point is basically wrong though.
- deleted 9y ago[deleted]