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Two-way and one-way finite automata, deterministic and nondeterministic and alternating, accept the same class of regular languages. However, transforming an automaton of one type to an equivalent automaton of another type incurs a blow-up in the number of states.
With a single infinite stack the model can parse (at least) any language that is computable by a Turing machine in linear time. [2] In particular, the language {a n b n c n} can be parsed by an algorithm which verifies first that there are the same number of a's and b's, then rewinds and verifies that there are the same number of b's and c's.
Two-wayness: Automata may read their input from left to right, or they may be allowed to move back-and-forth on the input, in a way similar to a Turing machine. Automata which can move back-and-forth on the input are called two-way finite automata. Acceptance condition. Acceptance of finite words: Same as described in the informal definition above.
Finite automata can be deterministic and nondeterministic, one-way (DFA, NFA) and two-way (2DFA, 2NFA). Other related classes are unambiguous (UFA), self-verifying (SVFA) and alternating (AFA) finite automata. These automata can also be two-way (2UFA, 2SVFA, 2AFA). All these machines can accept exactly the regular languages. However, the size ...
Union (cf. picture); that is, if the language L 1 is accepted by some NFA A 1 and L 2 by some A 2, then an NFA A u can be constructed that accepts the language L 1 ∪L 2. Intersection; similarly, from A 1 and A 2 an NFA A i can be constructed that accepts L 1 ∩L 2. Concatenation; Negation; similarly, from A 1 an NFA A n can be constructed ...
In the theory of computation, a branch of theoretical computer science, a pushdown automaton (PDA) is a type of automaton that employs a stack. Pushdown automata are used in theories about what can be computed by machines. They are more capable than finite-state machines but less capable than Turing machines (see below).
In the theory of computation and automata theory, the powerset construction or subset construction is a standard method for converting a nondeterministic finite automaton (NFA) into a deterministic finite automaton (DFA) which recognizes the same formal language. It is important in theory because it establishes that NFAs, despite their ...
Giovanni Pighizzini is an Italian theoretical computer scientist known for his work in formal language theory and particularly in state complexity of two-way finite automata. He earned his PhD in 1993 from the University of Milan, where he is a full professor since 2001.