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1
Module 18
•
NFA’s
–
nondeterministic transition functions
•
computations are trees, not paths
–
L(M) and LNFA
•
LFSA subset of LNFA
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Nondeterministic Finite State
Automata
NFA’s
3
Change:
δ
is a relation
•
For an FSA M,
δ
(q,a) results in one and
only one state for all states q and characters
a.
–
That is,
δ
is a function
•
For an NFA M,
δ
(q,a) can result in a set of
states
–
That is,
δ
is now a relation
–
Next step is not determined (nondeterministic)
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Example NFA
a
a
a
b
a,b
a,b
•
Why is this only an NFA and not an FSA?
Identify
as many reasons as you can.
5
Computing with NFA’s
•
Configurations: same as they are for FSA’s
•
Computations are different
–
Initial configuration is identical
–
However, there may be
several
next configurations or
there may be
none
.
•
Computation is no longer a “path” but is now a “graph” (often
a tree) rooted at the initial configuration
–
Definition of halting, accepting, and rejecting
configurations is identical
–
Definition of acceptance must be modified
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This note was uploaded on 07/25/2008 for the course CSE 460 taught by Professor Torng during the Fall '07 term at Michigan State University.
 Fall '07
 TORNG

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