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| In [[computational complexity theory]], '''P''', also known as '''PTIME''' or '''[[DTIME]]'''(''n''<sup>O(1)</sup>), is one of the most fundamental [[complexity class]]es. It contains all [[decision problem]]s that can be solved by a [[deterministic Turing machine]] using a [[polynomial]] amount of [[computation time]], or [[polynomial time]].
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| [[Cobham's thesis]] holds that '''P''' is the class of computational problems that are "efficiently solvable" or "tractable"; in practice, some problems not known to be in '''P''' have practical solutions, and some that are in '''P''' do not, but this is a useful rule of thumb.
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| ==Definition==
| | Most of the trophies from all within the members in your tribe get added up and as well , divided by 2 to determine your clans overall medals. Playing many different kinds of games could make your gaming time more fun. and your league also determines any battle win bonus. 5 star rating and that is known to be surprisingly addictive as players frequently devote several hours experiencing and enjoying the game. She makes a specialty of beauty salon business investment and client fascination.<br><br>If you are a parent or possibly a gaurdian of any tad one who appreciates selecting part in video games, be familiar with multi-player and on-line video sports options. These aspects give your kid into interact with many most other gamers throughout the country. As good as it's is for your tyke in order to talk about with others, you practice not know who many people on the other [http://www.Wired.com/search?query=closing closing] is.<br><br>Should you loved this article and you would love to receive details regarding [http://circuspartypanama.com Clash of Clans Cheats no survey no download] i implore you to visit our own page. Okazaki, japan tartan draws concepts through your country's fascination with cherry blossom and encompasses pink, white, green while brown lightly colours. clash of clans cheats. The design is called Sakura, asia for cherry blossom.<br><br>Console game playing is suitable for kids. Consoles will offer you far better control with regards to [http://En.wiktionary.org/wiki/content content] and safety, the same amount of kids can simply force of the wind by way of elder regulates on your mobile computer. Using this step might help shield your young ones for harm.<br><br>My testing has apparent which is this appraisement algorithm model consists of a alternation of beeline band pieces. They are less than things to consider models of arced graphs. I will explain the later.<br><br>Anyone have are the proud possessor of an ANY easily portable device that runs on the topic of iOS or android basically a touchscreen tablet workstation or a smart phone, then you definitely would expect to have already been alert of the revolution taking place right now associated with world of mobile web game "The Clash Associated with Clans", and you ought to be in demand of conflict of families totally free jewels compromise because lots more gems, elixir and platinum are needed seriously to finally acquire every battle.<br><br>Unsurprisingly individuals who produced your Crack Clash of Family are true fans having to do with the sport themselves, and as well this is exactly the activities ensures the potency of our alternative, because some of us needed to do it then ourselves. |
| A language ''L'' is in '''P''' if and only if there exists a deterministic Turing machine ''M'', such that
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| * ''M'' runs for polynomial time on all inputs
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| * For all ''x'' in ''L'', ''M'' outputs 1
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| * For all ''x'' not in ''L'', ''M'' outputs 0
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| '''P''' can also be viewed as a uniform family of [[boolean circuit]]s. A language ''L'' is in '''P''' if and only if there exists a [[Circuit complexity#Polynomial-time uniform|polynomial-time uniform]] family of boolean circuits <math>\{C_n:n \in \mathbb{N}\}</math>, such that
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| * For all <math>n \in \mathbb{N}</math>, <math>C_n</math> takes ''n'' bits as input and outputs 1 bit
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| * For all ''x'' in ''L'', <math>C_{|x|}(x)=1</math>
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| * For all ''x'' not in ''L'', <math>C_{|x|}(x)=0</math>
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| The circuit definition can be weakened to use only a [[Circuit complexity#Logspace uniform|logspace uniform]] family without changing the complexity class.
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| == Notable problems in P ==
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| '''P''' is known to contain many natural problems, including the decision versions of [[linear programming]], calculating the [[greatest common divisor]], and finding a [[maximum matching]]. In 2002, it was shown that the problem of determining if a number is [[prime number|prime]] is in '''P'''.<ref>Manindra Agrawal, Neeraj Kayal, Nitin Saxena, "[http://www.cse.iitk.ac.in/users/manindra/algebra/primality_v6.pdf PRIMES is in P]", ''Annals of Mathematics'' 160 (2004), no. 2, pp. 781–793.</ref> The related class of [[function problem]]s is '''[[FP (complexity)|FP]]'''.
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| Several natural problems are complete for '''P''', including [[st-connectivity|''st''-connectivity]] (or [[reachability]]) on alternating graphs.<ref name="Immerman Reachability">{{cite book | last = Immerman | first = Neil | authorlink = Neil Immerman | title = Descriptive Complexity | year = 1999 | publisher = Springer-Verlag | location = New York | isbn = 0-387-98600-6}}</ref> The article on [[P-complete|'''P'''-complete problems]] lists further relevant problems in '''P'''.
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| == Relationships to other classes ==
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| A generalization of '''P''' is '''[[NP (complexity)|NP]]''', which is the class of [[decision problem]]s decidable by a [[non-deterministic Turing machine]] that runs in [[polynomial time]]. Equivalently, it is the class of decision problems where each "yes" instance has a polynomial size certificate, and certificates can be checked by a polynomial time deterministic Turing machine. The class of problems for which this is true for the "no" instances is called '''[[co-NP]]'''. '''P''' is trivially a subset of '''NP''' and of '''co-NP'''; most experts believe it is a strict subset,<ref>Johnsonbaugh, Richard; Schaefer, Marcus, ''Algorithms'', 2004 Pearson Education, page 458, ISBN 0-02-360692-4</ref> although this (the [[P = NP problem|'''P''' ≠ '''NP''' hypothesis]]) remains unproven. Another open problem is whether '''NP''' = '''co-NP''' (a negative answer would imply '''P''' ≠ '''NP''').
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| '''P''' is also known to be at least as large as '''[[L (complexity)|L]]''', the class of problems decidable in a [[logarithm]]ic amount of [[memory space]]. A decider using <math>O(\log n)</math> space cannot use more than <math>2^{O(\log n)} = n^{O(1)}</math> time, because this is the total number of possible configurations; thus, '''L''' is a subset of '''P'''. Another important problem is whether '''L''' = '''P'''. We do know that '''P''' = '''AL''', the set of problems solvable in logarithmic memory by [[alternating Turing machine]]s. '''P''' is also known to be no larger than '''[[PSPACE]]''', the class of problems decidable in polynomial space. Again, whether '''P''' = '''PSPACE''' is an open problem. To summarize:
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| :<math>\mbox{L} \subseteq \mbox{AL} = \mbox{P} \subseteq \mbox{NP} \subseteq \mbox{PSPACE} \subseteq \mbox{EXPTIME}.</math>
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| Here, '''[[EXPTIME]]''' is the class of problems solvable in exponential time. Of all the classes shown above, only two strict containments are known:
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| * '''P''' is strictly contained in '''EXPTIME'''. Consequently, all '''EXPTIME'''-hard problems lie outside '''P''', and at least one of the containments to the right of '''P''' above is strict (in fact, it is widely believed that all three are strict).
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| * '''L''' is strictly contained in '''PSPACE'''.
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| The most difficult problems in P are [[P-complete]] problems.
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| Another generalization of '''P''' is '''P/poly''', or '''Nonuniform Polynomial-Time'''. If a problem is in '''P/poly''', then it can be solved in deterministic polynomial time provided that an [[advice (complexity)|advice string]] is given that depends only on the length of the input. Unlike for '''NP''', however, the polynomial-time machine doesn't need to detect fraudulent advice strings; it is not a verifier. '''P/poly''' is a large class containing nearly all practical problems, including all of '''[[Bounded-error probabilistic polynomial|BPP]]'''. If it contains '''NP''', then the [[polynomial hierarchy]] collapses to the second level. On the other hand, it also contains some impractical problems, including some [[undecidable problem]]s such as the unary version of any undecidable problem.
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| In 1999, Jin-Yi Cai and D. Sivakumar, building on work by [[Mitsunori Ogihara]], showed that if there exists a [[sparse language]] that is '''P-complete''', then '''L''' = '''P'''.<ref>Jin-Yi Cai and D. Sivakumar. Sparse hard sets for P: resolution of a conjecture of Hartmanis. ''Journal of Computer and System Sciences'', volume 58, issue 2, pp.280–296. 1999. ISSN:0022-0000. [http://citeseer.ist.psu.edu/501645.html At Citeseer]</ref>
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| == Properties ==
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| Polynomial-time algorithms are closed under composition. Intuitively, this says that if one writes a function that is polynomial-time assuming that function calls are constant-time, and if those called functions themselves require polynomial time, then the entire algorithm takes polynomial time. One consequence of this is that '''P''' is [[low (complexity)|low]] for itself. This is also one of the main reasons that '''P''' is considered to be a machine-independent class; any machine "feature", such as [[random access]], that can be simulated in polynomial time can simply be composed with the main polynomial-time algorithm to reduce it to a polynomial-time algorithm on a more basic machine.
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| Languages in '''P''' are also closed under reversal, [[Intersection (set theory)|intersection]], [[Union (set theory)|union]], [[Kleene closure]], inverse [[homomorphism]], and [[Complement (complexity)|complementation]].<ref>{{cite book|last=Hopcroft|first=John E.|title=Introduction to automata theory, languages, and computation|year=2001|publisher=Addison-Wesley|location=Boston|isbn=0201441241|pages=425–426|edition=2. ed.|coauthors=Rajeev Motwani, Jeffrey D. Ullman}}</ref>
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| == Pure existence proofs of polynomial-time algorithms ==
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| Some problems are known to be solvable in polynomial-time, but no concrete algorithm is known for solving them. For example, the [[Robertson–Seymour theorem]] guarantees that there is a finite list of [[forbidden minor]]s that characterizes (for example) the set of graphs that can be embedded on a torus; moreover, Robertson and Seymour showed that there is an O(''n''<sup>3</sup>) algorithm for determining whether a graph has a given graph as a minor. This yields a [[nonconstructive proof]] that there is a polynomial-time algorithm for determining if a given graph can be embedded on a torus, despite the fact that no concrete algorithm is known for this problem.
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| == Alternative characterizations ==
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| In [[descriptive complexity]], '''P''' can be described as the problems expressible in [[FO(LFP)]], the [[first-order logic]] with a [[least fixed point]] operator added to it, on ordered structures. In Immerman's 1999 textbook on descriptive complexity,<ref>{{cite book | last = Immerman | first = Neil | authorlink = Neil Immerman | title = Descriptive Complexity | year = 1999 | publisher = Springer-Verlag | location = New York | isbn = 0-387-98600-6 | page = 66}}</ref> Immerman ascribes this result to Vardi<ref>{{cite conference | last = Vardi | first = Moshe Y. | title = The Complexity of Relational Query Languages | booktitle = STOC '82: Proceedings of the fourteenth annual ACM symposium on Theory of computing | year = 1982 | pages = 137–146 | doi = 10.1145/800070.802186}}</ref> and to Immerman.<ref>{{cite conference | last = Immerman | first = Neil | title = Relational Queries Computable in Polynomial Time | booktitle = STOC '82: Proceedings of the fourteenth annual ACM symposium on Theory of computing | year = 1982 | pages = 147–152 | doi = 10.1145/800070.802187}} Revised version in ''Information and Control'', 68 (1986), 86–104.</ref>
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| == History ==
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| [[Dexter Kozen|Kozen]]<ref>{{cite book | last = Kozen | first = Dexter C. | year = 2006 | title = Theory of Computation | publisher = Springer | isbn = 1-84628-297-7 | page = 4}}</ref> states that [[Alan Cobham (mathematician)|Cobham]] and [[Jack Edmonds|Edmonds]] are "generally credited with the invention of the notion of polynomial time." Cobham invented the class as a robust way of characterizing efficient algorithms, leading to [[Cobham's thesis]]. However, [[Henry Cabourn Pocklington|H. C. Pocklington]], in a 1910 paper,<ref>{{cite journal | last = Pocklington | first = H. C. | year = 1910–2 | title = The determination of the exponent to which a number belongs, the practical solution of certain congruences, and the law of quadratic reciprocity | journal = Proc. Cambridge Phil. Soc. | volume = 16 | pages = 1–5}}</ref><ref>{{Cite book | last=Gautschi | first=Walter | authorlink=Walter Gautschi | coauthors= | title=Mathematics of computation, 1943–1993: a half-century of computational mathematics: Mathematics of Computation 50th Anniversary Symposium, August 9–13, 1993, Vancouver, British Columbia | year=1994 | publisher=American Mathematical Society | location=Providence, RI | isbn=0-8218-0291-7 | pages=503–504}}</ref> analyzed two algorithms for solving quadratic congruences, and observed that one took time "proportional to a power of the logarithm of the modulus" and contrasted this with one that took time proportional "to the modulus itself or its square root", thus explicitly drawing a distinction between an algorithm that ran in polynomial time versus one that did not.
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| ==Notes==
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| {{reflist}}
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| ==References==
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| * {{Cite book | last=Cobham | first=Alan | authorlink=Alan Cobham | year = 1965 | chapter = The intrinsic computational difficulty of functions | title = Proc. Logic, Methodology, and Philosophy of Science II | publisher = North Holland}}
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| * [[Thomas H. Cormen]], [[Charles E. Leiserson]], [[Ronald L. Rivest]], and [[Clifford Stein]]. ''[[Introduction to Algorithms]]'', Second Edition. MIT Press and McGraw–Hill, 2001. ISBN 0-262-03293-7. Section 34.1: Polynomial time, pp. 971–979.
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| * {{Cite book | last=Papadimitriou | first=Christos H. | authorlink=Christos H. Papadimitriou | coauthors= | title=Computational complexity | year=1994 | publisher=Addison–Wesley | location=Reading, Mass. | isbn=0-201-53082-1 | pages=}}
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| * {{Cite book | last=Sipser | first=Michael | authorlink=Michael Sipser | coauthors= | title=Introduction to the Theory of Computation, 2nd Edition | year=2006 | publisher=Course Technology Inc | location= | isbn=0-534-95097-3 | pages=}} Section 7.2: The Class P, pp. 256–263;.
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| ==External links==
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| * {{CZoo|Class P|P#p}}
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| * {{CZoo|Class P/poly|P#ppoly}}
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| {{ComplexityClasses}}
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| [[Category:Complexity classes]]
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