Talk:Nondeterministic finite automaton

message: A number of books describe only one start state. Does that make any difference?
:If you have multiple start states, then you might find the concept of a semiautomaton more useful. linas 20:21, 19 May 2007 (UTC)
thread_title:  About multiple start states 

message: This page is well-done, but I think it'd be nice if the diagram demonstrated the nondeterminism a little better, by having two edges with the same label coming out a single node somewhere. Deco 21:37, 12 Nov 2004 (UTC)
thread_title:  Diagram 

message: While this article seems very succinct, the content is very much targeted towards computer scientists. As a non-computer scientist having read both 'Deterministic finite state machine' and 'Nondeterministic finite state machine' I still don't understand either explanations. I'm guessing nondeterministic finite state machines refers to computer algorithms which perform 'trial and error' calculations to a finite problem in order to derive a finite set of solutions. However, this certainly isn't clear from the article so I may be way off. Anyhow, can I encourage someone who does understand this subject to consider pitching it at a much wider audience. --angusj 00:32, 17 September 2005 (UTC)
replies: text: Is it better now? linas 21:46, 19 May 2007 (UTC)

text: No that is incorrect; that is not what NFA's are for. In particular, NFA's do have particular details that cannot be ignored. linas 21:48, 19 May 2007 (UTC)
thread_title:  Target Audience 

message: There is an inconsistency in the two definitions in this Article:
"A nondeterministic finite state automaton (NFA) is a 5-tuple, (S, Σ, T, s0, A), consisting of
a finite set of states (S) 
a finite set of input symbols (Σ)
 
a transition function (T : S × (Σ ∪{ε}) → P(S)). 
an initial (or start) state s0 such that s0 ∈ S 
a set of states A distinguished as accepting (or final) states (A ⊆ S) 
where P(S) is the power set of S, ε is the empty string, and Σ is the input symbol alphabet.
Let M be an NFA such that M = (S, Σ, T, s0, A), and X be a string over the alphabet Σ. M accepts the string X if there exist both a representation of X of the form x1x2 ... xn, xi ∈ (Σ ∪{ε}), and a sequence of states r0,r1, ..., rn, ri ∈ S, meeting the following conditions:
r0 ∈ s0 
ri ∈ T(ri-1, xi ), for i = 1, ..., n
 
rn ∈ A. "
In the first definition, the author defines s_{0} as an element of S.  
In the second definition, the author defines r_{0} \in s_{0} which implies s_{0} is a subset of S.
--CBKAtTopsails 18:35, 27 April 2007 (UTC)
replies: text: This appears to have been fixed in the current article. linas 21:48, 19 May 2007 (UTC)
thread_title:  Inconsistency 

message: I think that a technical discussion about automata with an infinite number of states is misplaced in an article about NFAs. I cut and pasted the part in question and place it here:
:For non-deterministic automata with a countably infinite set of states, the powerset construction gives a deterministic automaton with a continuum of states (since the powerset of the countable infinity is the continuum: 2^{\aleph_0}=\aleph_1). In such a case, the set of states must be endowed with a topology in order for the state transitions to be meaningful. Such systems are studied as topological automata.
If you feel that passage should be reinserted, please argue. 23:09, 6 May 2009 (UTC)
replies: text: I think a better place for this is powerset construction. However, I wouldn't mind seeing this article merged into a larger article on nondeterministic state machines in general. Dcoetzee 23:12, 6 May 2009 (UTC)
replies: text: I think the concept is both of central importance and there is enough content to justify an article on its on right. I think discussing too many variants and generalizations will disturb most readers.Hermel (talk) 13:03, 7 May 2009 (UTC)
thread_title:  Infinite number of states 

message: This page is entirely a discussion of the formal theory of NFAs.  But in the programming world when people talk about regular expression engines they use the term NFA informally .  For example PCRE is described as an NFA engine, even though it is strictly not.
Shouldn't the article at least acknowledge that informal usage in industry differs from what is being discussed?  —Preceding unsigned comment added by 72.10.62.12 (talk) 20:12, 11 May 2011 (UTC)
thread_title:  Formal vs Informal usage 

message: There is a move discussion in progress which affects this page. Please participate at Talk:Deterministic finite-state machine - Requested move and not in this talk page section. Thank you.  —RM bot 15:20, 25 November 2011 (UTC)
thread_title: Move discussion in progress

message: I don't think that reference to abbreviations "NDFA" and "NDFSM" is needed, because rest of the article and wikipedia does not refer to the abbreviations. If User:Urhixidur doesnot object then I will remove it. Ashutosh Gupta (talk) 08:03, 21 April 2012 (UTC)
thread_title: unnecessary abbreviations, NDFA and NDFSM

message: This page uses symbols that don't render properly in IE8 running on WinXP.  Any thoughts/objections regarding switching to LaTex? Morfusmax (talk) 18:53, 28 May 2013 (UTC)
thread_title:  LaTeX? 

message: The introduction states an NFA is not required to read an input symbol for each state transition.
Such transitions without reading an input symbol are ε-moves.
However, later in the introduction ε-moves are considered to be an extension to NFAs (with a link to the separate article Nondeterministic_finite_automaton_with_%CE%B5-moves).
The formal definition also does not support ε-moves.
This change introduced the statement without extending the formal definition or merging with Nondeterministic_finite_automaton_with_%CE%B5-moves.
I think the first paragraph of the introduction can simply be changed to:
In automata theory, a finite state machine is called a deterministic finite automaton (DFA), if each of its transitions is uniquely determined by its source state and input symbol.
A nondeterministic finite automaton (NFA), or nondeterministic finite state machine, does not need to obey these restrictions. In particular, every DFA is also an NFA. --PapaNappa (talk) 14:57, 26 August 2015 (UTC)
replies: text: See merge proposal, below. QVVERTYVS (hm?) 17:07, 21 October 2015 (UTC)
thread_title:  Inconsistency with ε-moves 

message: The current setup of these two articles suggests that unqualified "NFA" means "NFA without ε-transitions". I doubt that it does; e.g., how many descriptions of Thompson's construction care to make the distinction? Since NFA might mean both kinds of automaton depending on context, I think we should merge. QVVERTYVS (hm?) 17:06, 21 October 2015 (UTC)
replies: text: I totally agree. I think we should unify the formal definition, and keep both examples. PapaNappa (talk) 12:52, 24 November 2015 (UTC)
thread_title:  Proposed merge with [[Nondeterministic finite automaton with ε-moves]] 

message: Substituted at 20:09, 1 May 2016 (UTC)
thread_title: Assessment comment