Resting potential: Difference between revisions
en>Tryptofish →Summary of resting potential values in different types of cells: better to show range, also make all minus signs n-dashes |
en>Tryptofish Undid revision 584837955 by 137.43.182.163 (talk) correct spelling, verified by Google search |
||
Line 1: | Line 1: | ||
In [[automata theory]], an '''alternating finite automaton''' (AFA) is a [[nondeterministic finite automaton]] whose transitions are divided into ''[[existential quantification|existential]]'' and ''[[universal quantification|universal]]'' transitions. For example, let ''A'' be an alternating [[automaton]]. | |||
* For an existential transition <math>(q, a, q_1 \vee q_2)</math>, ''A'' nondeterministically chooses to switch the state to either <math>q_1</math> or <math>q_2</math>, reading ''a''. Thus, behaving like a regular [[nondeterministic finite automaton]]. | |||
* For a universal transition <math>(q, a, q_1 \wedge q_2)</math>, ''A'' moves to <math>q_1</math> '''and''' <math>q_2</math>, reading ''a'', simulating the behavior of a parallel machine. | |||
Note that due to the universal quantification a run is represented by a run ''tree''. ''A'' accepts a word ''w'', if there ''exists'' a run tree on ''w'' such that ''every'' path ends in an accepting state. | |||
A basic theorem tells that any AFA is equivalent to an [[non-deterministic finite automaton]] (NFA) by performing a similar kind of powerset construction as it is used for the transformation of an NFA to a [[deterministic finite automaton]] (DFA). This construction converts an AFA with ''k'' states to an NFA with up to <math>2^k</math> states. | |||
An alternative model which is frequently used is the one where Boolean combinations are represented as ''clauses''. For instance, one could assume the combinations to be in [[Disjunctive normal form|Disjunctive Normal Form]] so that <math>\{\{q_1\},\{q_2,q_3\}\}</math> would represent <math>q_1 \vee (q_2 \wedge q_3)</math>. The state '''tt''' (''true'') is represented by <math>\{\{\}\}</math> in this case and '''ff''' (''false'') by <math>\varnothing</math>. | |||
This clause representation is usually more efficient. | |||
==Formal Definition== | |||
An alternating finite automaton (AFA) is a [[n-tuple|6-tuple]], | |||
<math>(S(\exists), S(\forall), \Sigma, \delta, P_0, F)</math>, where | |||
*<math>S(\exists)</math> is a finite set of existential states. Also commonly represented as <math>S(\vee)</math>. | |||
*<math>S(\forall)</math> is a finite set of universal states. Also commonly represented as <math>S(\wedge)</math>. | |||
*<math>\ \Sigma</math> is a finite set of input symbols. | |||
*<math>\ \delta</math> is a set of transition [[function (mathematics)|functions]] to next state <math>(S(\exists) \cup S(\forall)) \times (\Sigma \cup \{ \varepsilon \} ) \to 2^{S(\exists) \cup S(\forall)}</math>. | |||
*<math>\ P_0</math> is the initial (start) state, such that <math>P_0 \in S(\exists) \cup S(\forall)</math>. | |||
*<math>\ F</math> is a set of accepting (final) states such that <math>F \subseteq S(\exists) \cup S(\forall)</math>. | |||
==References== | |||
* {{cite book | title=Theories of Computability | first=Nicholas | last=Pippenger | authorlink=Nick Pippenger | publisher=[[Cambridge University Press]] | year=1997 | isbn=0-521-55380-6 }} | |||
{{DEFAULTSORT:Alternating Finite Automaton}} | |||
[[Category:Automata theory]] | |||
{{comp-sci-theory-stub}} |
Revision as of 16:32, 6 December 2013
In automata theory, an alternating finite automaton (AFA) is a nondeterministic finite automaton whose transitions are divided into existential and universal transitions. For example, let A be an alternating automaton.
- For an existential transition , A nondeterministically chooses to switch the state to either or , reading a. Thus, behaving like a regular nondeterministic finite automaton.
- For a universal transition , A moves to and , reading a, simulating the behavior of a parallel machine.
Note that due to the universal quantification a run is represented by a run tree. A accepts a word w, if there exists a run tree on w such that every path ends in an accepting state.
A basic theorem tells that any AFA is equivalent to an non-deterministic finite automaton (NFA) by performing a similar kind of powerset construction as it is used for the transformation of an NFA to a deterministic finite automaton (DFA). This construction converts an AFA with k states to an NFA with up to states.
An alternative model which is frequently used is the one where Boolean combinations are represented as clauses. For instance, one could assume the combinations to be in Disjunctive Normal Form so that would represent . The state tt (true) is represented by in this case and ff (false) by . This clause representation is usually more efficient.
Formal Definition
An alternating finite automaton (AFA) is a 6-tuple, , where
- is a finite set of existential states. Also commonly represented as .
- is a finite set of universal states. Also commonly represented as .
- is a finite set of input symbols.
- is a set of transition functions to next state .
- is the initial (start) state, such that .
- is a set of accepting (final) states such that .
References
- 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534