# 05 - Lecture 5 Nondeterministic Finite Automata In a DFA each symbol read causes a transition to the next state which is completely determined by

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Lecture 5: Nondeterministic Finite Automata In a DFA, each symbol read causes a transition to the next state, which is completely determined by the cur- rent state and current symbol (i.e., there is ex- actly one next state). In an NFA, some state may have more than one outgoing edge labeled with the same symbol some edges may be labeled with e , the empty word. Therefore, an input string may drive the automaton through more than one path. In addition, some state may not have any outgoing edge labeled with a particular symbol (can get stuck). 1

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Nondeterministic fnite automata (NFA) NFA are not realistic models of computers. They are only a convenient speci±cation of ±nite au- tomata – NFA are much easier to design than DFA. We will show in the next lecture that every NFA can be converted into an equivalent DFA; that is, non-determinism does not provide additional computation power. 2
Nondeterministic fnite automata (NFA) Example: L =( ab aba ) DFA: a a a,b b a b b a b NFAs: 1 q q 2 q 0 q 01 q q 2 b a e a b a b a 3

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## This note was uploaded on 09/22/2011 for the course COMP 272 taught by Professor Prof.tai during the Spring '10 term at HKUST.

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05 - Lecture 5 Nondeterministic Finite Automata In a DFA each symbol read causes a transition to the next state which is completely determined by

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