Re: quantum Computing

["Perry E. Metzger" <perry@imsi.com>]

Mike McNally says:
> 
> Rick Busdiecker writes:
>  > No, NFA is acceptable and correct, it's Non-determinisic Finite
>  > Automaton.  A non-deterministic Turing machine is a perfectly
>  > reasonable example, however.
> 
> Uhh, isn't it the case that a Turing machine can simulate an NFA, but
> not the reverse?  An NFA has no tape, and therefore is not as powerful
> an automaton as a Turing machine.  Thus an NFA can be implemented by
> an NTM, but not the reverse.
> 
> I think.

Correct. The hierarchy as I remember it is roughly (from least to most
powerful in terms of size of the recognizable languages) FAs, PDAs
(that is, deterministic push-down automata), NPDAs, TMs. Its been a
while, but I seem to recall that non-deterministic pushdown automata
could recognise some languages that deterministic ones could not.

Perry