Properties of Multihead Two-way Probabilistic Nite Automata
نویسنده
چکیده
We present properties of multihead two-way probabilistic nite automata that parallel those of their deterministic and nondeterministic counterparts. We deene multihead proba-bilistic nite automata with log-space constructible transition probabilities, and we describe a simple technique to simulate these automata by standard log-space probabilistic Turing machines. Next, we represent log-space probabilistic complexity classes as proper hierarchies based on corresponding multihead two-way probabilistic nite automata, and we show their (deterministic log-space) reducibility to the second levels of these hierarchies. We relate the number of heads of a multihead probabilistic nite automaton to the bandwidth of its connguration transition matrix for an input string; partially based on this relation, we nd an apparently easier log-space complete problem for PL (the class of languages recognized by log-space unbounded-error probabilistic Turing machines), and we investigate possibilities for a space-eecient deterministic simulation of probabilistic automata.
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