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[[File:P np np-complete np-hard.svg|thumb|300px|right|[[Euler diagram]] for [[P (complexity)|P]], [[NP (complexity)|NP]], NP-complete, and [[NP-hard]] set of problems. The left side is valid under the assumption that [[P versus NP problem |P≠NP]], while the right side is valid under the assumption that P=NP (except that the empty language and its complement are never NP-complete)]]
{{simplify|date=July 2012}}In [[computational complexity theory]], the [[complexity class]] '''NP-complete''' (abbreviated '''NP-C''' or '''NPC''') is a class of [[decision problem]]s. A decision problem ''L'' is NP-complete if it is in the set of [[NP (complexity)|NP]] problems and also in the set of [[NP-hard]] problems. The abbreviation '''NP''' refers to "[[Nondeterministic algorithm|nondeterministic]] [[polynomial time]]."


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Although any given solution to an NP-complete problem can be verified quickly (in polynomial time), there is no known efficient way to locate a solution in the first place; indeed, the most notable characteristic of NP-complete problems is that no fast solution to them is known. That is, the time required to solve the problem using any currently known [[algorithm]] increases very quickly as the size of the problem grows. This means that the time required to solve even moderately sized versions of many of these problems can easily reach into the billions or trillions of years, using any amount of computing power available today. As a consequence, determining whether or not it is possible to solve these problems quickly, called the [[P versus NP problem]], is one of the principal [[List of open problems in computer science|unsolved problems in computer science]] today.


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While a method for computing the solutions to NP-complete problems using a reasonable amount of time remains undiscovered, [[computer scientist]]s and [[computer programmer|programmer]]s still frequently encounter NP-complete problems. NP-complete problems are often addressed by using [[heuristic (computer science)|heuristic]] methods and [[approximation algorithm]]s.
 
==Formal overview==
 
NP-complete is a [[subset]] of [[NP (complexity)|NP]], the set of all [[decision problems]] whose solutions can be verified in polynomial time; ''NP'' may be equivalently defined as the set of decision problems that can be solved in polynomial time on a [[nondeterministic Turing machine]]. A problem ''p'' in NP is also NP-complete if every other problem in NP can be transformed into ''p'' in polynomial time. NP-complete can also be used as an adjective: problems in the class NP-complete are known as NP-complete problems.
 
NP-complete problems are studied because the ability to quickly verify solutions to a problem (NP) seems to correlate with the ability to quickly solve that problem ([[P (complexity)|P]]). It is not known whether every problem in NP can be quickly solved—this is called the [[P = NP problem]]. But if ''any single problem'' in NP-complete can be solved quickly, then ''every problem in NP'' can also be quickly solved, because the definition of an NP-complete problem states that every problem in NP must be quickly reducible to every problem in NP-complete (that is, it can be reduced in polynomial time). Because of this, it is often said that the NP-complete problems are ''harder'' or ''more difficult'' than NP problems in general.
 
== Formal definition of NP-completeness ==
{{Main|P %3D NP problem#Formal definition for NP-completeness|l1=formal definition for NP-completeness (article ''P = NP'')}}
A decision problem <math>\scriptstyle C</math> is NP-complete if:
# <math>\scriptstyle C</math> is in NP, and
# Every problem in NP is [[Many-one reduction|reducible]] to <math>\scriptstyle C</math> in polynomial time.
 
<math>\scriptstyle C</math> can be shown to be in NP by demonstrating that a candidate solution to <math>\scriptstyle C</math> can be verified in polynomial time.
 
Note that a problem satisfying condition 2 is said to be [[NP-hard]], whether or not it satisfies condition 1.
 
A consequence of this definition is that if we had a polynomial time algorithm (on a [[Universal Turing machine|UTM]], or any other [[Turing completeness|Turing-equivalent]] [[abstract machine]]) for <math>\scriptstyle C</math>, we could solve all problems in NP in polynomial time.
 
==Background==
The concept of NP-completeness was introduced in 1971 by [[Stephen Cook]] in a paper entitled ''The complexity of theorem-proving procedures'' on pages 151–158 of the ''Proceedings of the 3rd Annual ACM Symposium on Theory of Computing'', though the term ''NP-complete'' did not appear anywhere in his paper. At that [[computer science]] conference, there was a fierce debate among the computer scientists about whether NP-complete problems could be solved in polynomial time on a [[deterministic]] [[Turing machine]]. [[John Hopcroft]] brought everyone at the conference to a consensus that the question of whether NP-complete problems are solvable in polynomial time should be put off to be solved at some later date, since nobody had any formal proofs for their claims one way or the other.  This is known as the question of whether P=NP.
 
Nobody has yet been able to determine conclusively whether NP-complete problems are in fact solvable in polynomial time, making this one of the great [[unsolved problems of mathematics]].  The [[Clay Mathematics Institute]] is offering a US $1 million reward to anyone who has a formal proof that P=NP or that P≠NP.
 
In the celebrated [[Cook's theorem|Cook-Levin theorem]] (independently proved by [[Leonid Levin]]), Cook proved that the [[Boolean satisfiability problem]] is NP-complete (a simpler, but still highly technical [[Proof that Boolean satisfiability problem is NP-complete|proof of this]] is available). In 1972, [[Richard Karp]] proved that several other problems were also NP-complete (see [[Karp's 21 NP-complete problems]]); thus there is a class of NP-complete problems (besides the Boolean satisfiability problem). Since Cook's original results, thousands of other problems have been shown to be NP-complete by reductions from other problems previously shown to be NP-complete; many of these problems are collected in [[Michael Garey|Garey]] and [[David S. Johnson|Johnson's]] 1979 book ''[[Computers and Intractability: A Guide to the Theory of NP-Completeness]]''.<ref name="GareyJohnson">{{cite book|last1=Garey|first1=Michael&nbsp;R.|authorlink1=Michael R. Garey|last2=Johnson|first2=D.&nbsp;S.|authorlink2=David S. Johnson|title=[[Computers and Intractability: A Guide to the Theory of NP-Completeness]]|year=1979 |isbn=0-7167-1045-5|pages=x+338|url=|doi=|series=A Series of Books in the Mathematical Sciences|editor=[[Victor Klee]]|publisher=W.&nbsp;H.&nbsp;Freeman and Co.|location=San Francisco, Calif.|mr=519066|ref=harv}}</ref>
For more details refer to ''Introduction to the Design and Analysis of Algorithms'' by Anany Levitin.
 
==NP-complete problems==
{{Main|List of NP-complete problems}}
[[File:Relative NPC chart.svg|thumb|right|Some NP-complete problems, indicating the [[reduction (complexity)|reductions]] typically used to prove their NP-completeness]]
 
An interesting example is the [[graph isomorphism problem]], the [[graph theory]] problem of determining whether a [[graph isomorphism]] exists between two graphs. Two graphs are [[isomorphic]] if one can be [[isomorphism|transformed]] into the other simply by renaming [[vertex (graph theory)|vertices]]. Consider these two problems:
*Graph Isomorphism: Is graph G<sub>1</sub> isomorphic to graph G<sub>2</sub>?
*Subgraph Isomorphism: Is graph G<sub>1</sub> isomorphic to a subgraph of graph G<sub>2</sub>?
 
The Subgraph Isomorphism problem is NP-complete. The graph isomorphism problem is suspected to be neither in P nor NP-complete, though it is in NP. This is an example of a problem that is thought to be '''hard''', but isn't thought to be NP-complete.
 
The easiest way to prove that some new problem is NP-complete is first to prove that it is in NP, and then to reduce some known NP-complete problem to it. Therefore, it is useful to know a variety of NP-complete problems. The list below contains some well-known problems that are NP-complete when expressed as decision problems.
<div style="-moz-column-count:2; column-count:2;">
*[[Boolean satisfiability problem|Boolean satisfiability problem (Sat.)]]
*[[Knapsack problem]]
*[[Hamiltonian path problem]]
*[[Travelling salesman problem]]
*[[Subgraph isomorphism problem]]
*[[Subset sum problem]]
*[[Clique problem]]
*[[Vertex cover problem]]
*[[Independent set problem]]
*[[Dominating set problem]]
*[[Graph coloring problem]]
</div>
 
To the right is a diagram of some of the problems and the [[reduction (complexity)|reductions]] typically used to prove their NP-completeness. In this diagram, an arrow from one problem to another indicates the direction of the reduction.  Note that this diagram is misleading as a description of the mathematical relationship between these problems, as there exists a [[polynomial-time reduction]] between any two NP-complete problems; but it indicates where demonstrating this polynomial-time reduction has been easiest.
 
There is often only a small difference between a problem in P and an NP-complete problem. For example, the [[3-satisfiability]] problem, a restriction of the boolean satisfiability problem, remains NP-complete, whereas the slightly more restricted [[2-satisfiability]] problem is in P (specifically, [[NL-complete]]), and the slightly more general max. 2-sat. problem is again NP-complete. Determining whether a graph can be colored with 2 colors is in P, but with 3 colors is NP-complete, even when restricted to [[planar graph]]s. Determining if a graph is a [[cycle graph|cycle]] or is [[bipartite graph|bipartite]] is very easy (in [[L (complexity)|L]]), but finding a maximum bipartite or a maximum cycle subgraph is NP-complete. A solution of the [[knapsack problem]] within any fixed percentage of the optimal solution can be computed in polynomial time, but finding the optimal solution is NP-complete.
 
==Solving NP-complete problems==
At present, all known algorithms for NP-complete problems require time that is [[superpolynomial]] in the input size, and it is unknown whether there are any faster algorithms.
 
The following techniques can be applied to solve computational problems in general, and they often give rise to substantially faster algorithms:
* [[Approximation algorithm|Approximation]]: Instead of searching for an optimal solution, search for an "almost" optimal one.
* [[Randomized algorithm|Randomization]]: Use randomness to get a faster average [[running time]], and allow the algorithm to fail with some small probability. Note: The [[Monte Carlo method]] is not an example of an efficient algorithm, although evolutionary approaches like [[Genetic algorithm]]s may be.
* Restriction: By restricting the structure of the input (e.g., to planar graphs), faster algorithms are usually possible.
* [[Parameterized complexity|Parameterization]]: Often there are fast algorithms if certain parameters of the input are fixed.
* [[Heuristic (computer science)|Heuristic]]: An algorithm that works "reasonably well" in many cases, but for which there is no proof that it is both always fast and always produces a good result.  [[Metaheuristic]] approaches are often used.
 
One example of a heuristic algorithm is a suboptimal <math>\scriptstyle O(n\log n)</math> [[greedy coloring|greedy coloring algorithm]] used for [[graph coloring problem|graph coloring]] during the [[register allocation]] phase of some compilers, a technique called [[graph-coloring global register allocation]]. Each vertex is a variable, edges are drawn between variables which are being used at the same time, and colors indicate the register assigned to each variable. Because most [[RISC]] machines have a fairly large number of general-purpose registers, even a heuristic approach is effective for this application.
 
== Completeness under different types of reduction ==
In the definition of NP-complete given above, the term ''reduction'' was used in the technical meaning of a polynomial-time many-one reduction.
 
Another type of reduction is polynomial-time Turing reduction. A problem <math>\scriptstyle X</math> is polynomial-time Turing-reducible to a problem <math>\scriptstyle Y</math> if, given a subroutine that solves <math>\scriptstyle Y</math> in polynomial time, one could write a program that calls this subroutine and solves <math>\scriptstyle X</math> in polynomial time.  This contrasts with many-one reducibility, which has the restriction that the program can only call the subroutine once, and the return value of the subroutine must be the return value of the program.
 
If one defines the analogue to NP-complete with Turing reductions instead of  many-one reductions, the resulting set of problems won't be smaller than NP-complete; it is an open question whether it will be any larger.
 
Another type of reduction that is also often used to define NP-completeness is the [[logarithmic-space many-one reduction]] which is a many-one reduction that can be computed with only a logarithmic amount of space. Since every computation that can be done in [[logarithmic space]] can also be done in polynomial time it follows that if there is a logarithmic-space many-one reduction then there is also a polynomial-time many-one reduction. This type of reduction is more refined than the more usual polynomial-time many-one reductions and it allows us to distinguish more classes such as [[P-complete]]. Whether under these types of reductions the definition of NP-complete changes is still an open problem. All currently known NP-complete problems are NP-complete under log space reductions. Indeed, all currently known NP-complete problems remain NP-complete even under much weaker reductions.<ref>{{Cite journal | doi=10.1006/jcss.1998.1583 | last1=Agrawal | first1=M. | author1-link=Manindra Agrawal | last2=Allender | first2=E. | last3=Rudich | first3=Steven | author3-link=Steven Rudich | title=Reductions in Circuit Complexity: An Isomorphism Theorem and a Gap Theorem | publisher=[[Academic Press]]  | year=1998 | journal=Journal of Computer and System Sciences | issn=1090-2724 | volume=57 | issue=2 | pages=127–143 | postscript=<!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. --> | ref=harv}}</ref> It is known, however, that AC<sup>0</sup> reductions define a strictly smaller class than polynomial-time reductions.<ref>{{Cite journal | last1=Agrawal | first1=M. | author1-link=Manindra Agrawal | last2=Allender | first2=E. | last3=Impagliazzo | first3=R. | last4=Pitassi | first4=T. | author4-link = Toniann Pitassi | last5=Rudich | first5=Steven | author5-link=Steven Rudich | title=Reducing the complexity of reductions | doi=10.1007/s00037-001-8191-1 | publisher=Birkhäuser Basel | year=2001 | journal=Computational Complexity | issn=1016-3328 | volume=10 | pages=117–138 | issue=2 | postscript=<!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}} | ref=harv}}
</ref>
 
== Naming ==
According to [[Donald Knuth]], the name "NP-complete" was popularized by [[Alfred Aho]], [[John Hopcroft]] and [[Jeffrey Ullman]] in their celebrated textbook "The Design and Analysis of Computer Algorithms". He reports that they introduced the change in the [[galley proofs]] for the book (from "polynomially-complete"), in accordance with the results of a poll he had conducted of the [[Theoretical computer science|Theoretical Computer Science]] community.<ref>[[Don Knuth]], Tracy Larrabee, and Paul M. Roberts, ''[http://tex.loria.fr/typographie/mathwriting.pdf Mathematical Writing]'' § 25, ''MAA Notes No. 14'', MAA, 1989 (also [[Stanford University|Stanford]] Technical Report, 1987).</ref> Other suggestions made in the poll<ref>{{Cite journal
| doi = 10.1145/1811129.1811130
| volume = 6
| issue = 1
| pages = 12–18
| last = Knuth
| first = D. F.
| title = A terminological proposal
| journal = SIGACT News
| accessdate = 2010-08-28
| year = 1974
| url = http://portal.acm.org/citation.cfm?id=1811130
| ref = harv
}}</ref> included  "[[Labours of Hercules|Herculean]]", "formidable", [[Kenneth Steiglitz|Steiglitz]]'s "hard-boiled" in honor of Cook, and Shen Lin's acronym "PET", which stood for "probably exponential time", but depending on which way the [[P versus NP problem]] went, could stand for "provably exponential time" or "previously exponential time".<ref>See the poll, or [http://www.cs.princeton.edu/~wayne/kleinberg-tardos/08np-complete-2x2.pdf].</ref>
 
== Common misconceptions ==
 
The following misconceptions are frequent.<ref>{{Cite news|url=http://www.nature.com/news/2000/000113/full/news000113-10.html
 
|doi=10.1038/news000113-10
|title=DNA computer helps travelling salesman
|first=Philip|last= Ball
 
}}</ref>
* ''"NP-complete problems are the most difficult known problems."'' Since NP-complete problems are in NP, their running time is at most exponential. However, some problems <!-- the next word is PROVABLY (as in "to prove" something), not PROBABLY. Do not 'fix' it! -->provably<!-- proVVVVably --> require more time, for example [[Presburger arithmetic]].
* ''"NP-complete problems are difficult because there are so many different solutions."'' On the one hand, there are many problems that have a solution space just as large, but can be solved in polynomial time (for example [[minimum spanning tree]]). On the other hand, there are NP-problems with at most one solution that are NP-hard under randomized polynomial-time reduction (see [[Valiant–Vazirani theorem]]).
* ''"Solving NP-complete problems requires exponential time."'' First, this would imply P ≠ NP, which is still an unsolved question. Further, some NP-complete problems actually have algorithms running in superpolynomial, but subexponential time. For example, the [[Independent set problem|Independent set]] and [[Dominating set problem|Dominating set]] problems are NP-complete when restricted to [[planar graph]]s, but can be solved in subexponential time on [[planar graph]]s using the [[planar separator theorem]].<ref>{{harvtxt|Bern|1990}}; {{harvtxt|Deĭneko|Klinz|Woeginger|2006}}; {{harvtxt|Dorn|Penninks|Bodlaender|Fomin|2005}}; {{harvtxt|Lipton|Tarjan|1980}}.</ref>
* ''"All instances of an NP-complete problem are difficult."'' Often some instances, or even most instances, may be easy to solve within polynomial time. However, unless P=NP, any polynomial-time algorithm must asymptotically be wrong on more than polynomially many of the exponentially many inputs of a certain size.<ref>{{Cite doi|10.1145/2421119.2421135}}</ref>
* ''"If P=NP, all cryptographic ciphers can be broken."'' A polynomial-time problem can be very difficult to solve in practice if the polynomial's degree or constants are large enough. For example, ciphers with a fixed key length, such as [[Advanced Encryption Standard]], can all be broken in constant time (and are thus already in P), though that constant may exceed the age of the universe.
 
==See also==
* [[Almost complete]]
* [[Gadget (computer science)]]
* [[Ladner's theorem]]
* [[List of NP-complete problems]]
* [[NP-hard]]
* [[P = NP problem]]
* [[Strongly NP-complete]]
* [[Wicked problem]]
 
==Notes==
{{reflist|2}}
 
==References==
{{refbegin|colwidth=30em}}
* {{Cite book
| last = Garey
| first = M.R.
| authorlink = Michael Garey
| coauthors = [[David S. Johnson|Johnson, D.S.]]
| title = [[Computers and Intractability: A Guide to the Theory of NP-Completeness]]
| year = 1979
| publisher = W.H. Freeman
| location = New York
| isbn =  0-7167-1045-5
}}  This book is a classic, developing the theory, then cataloguing ''many'' NP-Complete problems.
* {{Cite conference
| last = Cook
| first = S.A.
| authorlink = Stephen A. Cook
| title = The complexity of theorem proving procedures
| booktitle = Proceedings, Third Annual ACM Symposium on the Theory of Computing, ACM, New York
| year = 1971
| pages = 151–158
| doi = 10.1145/800157.805047
}}
* {{cite web
| last = Dunne
| first = P.E
| title = An annotated list of selected NP-complete problems
| publisher = COMP202, Dept. of Computer Science, [[University of Liverpool]]
| url = http://www.csc.liv.ac.uk/~ped/teachadmin/COMP202/annotated_np.html
| accessdate = 2008-06-21
}}
* {{cite web
| last = Crescenzi
| first = P.
| coauthors = Kann, V.; Halldórsson, M.; [[Marek Karpinski|Karpinski, M.]]; Woeginger, G
| title = A compendium of NP optimization problems
| publisher = KTH NADA, Stockholm
| url = http://www.nada.kth.se/~viggo/problemlist/compendium.html
| accessdate = 2008-06-21
}}
* {{cite web
| last = Dahlke
| first = K
| title = NP-complete problems
| work = Math Reference Project
| url = http://www.mathreference.com/lan-cx-np,intro.html
| accessdate = 2008-06-21
}}
* {{cite web
| last = Karlsson
| first = R
| title = Lecture 8: NP-complete problems
| publisher = Dept. of Computer Science, Lund University, Sweden
| url = http://www.cs.lth.se/home/Rolf_Karlsson/bk/lect8.pdf
| format = PDF
| accessdate = 2008-06-21
}} {{Dead link|date=October 2010|bot=H3llBot}}
* {{cite web
| last = Sun
| first = H.M
| title = The theory of NP-completeness
| publisher = Information Security Laboratory, Dept. of Computer Science, [[National Tsing Hua University]], Hsinchu City, Taiwan
| url = http://is.cs.nthu.edu.tw/course/2008Spring/cs431102/hmsunCh08.ppt
| format = PPT
| accessdate = 2008-06-21
}}
* {{cite web
| last = Jiang
| first = J.R
| title = The theory of NP-completeness
| publisher = Dept. of Computer Science and Information Engineering, [[National Central University]], Jhongli City, Taiwan
| url = http://www.csie.ncu.edu.tw/%7Ejrjiang/alg2006/NPC-3.ppt
| format = PPT
| accessdate = 2008-06-21
}}
* {{Cite book
| last = Cormen
| first = T.H.
| authorlink = Thomas H. Cormen
| coauthors = [[Charles E. Leiserson|Leiserson, C.E.]], [[Ronald L. Rivest|Rivest, R.L.]]; [[Clifford Stein|Stein, C.]]
| title = [[Introduction to Algorithms]]
| edition = 2nd
| year = 2001
| publisher = MIT Press and McGraw-Hill
| isbn = 0-262-03293-7
| pages = Chapter 34: NP–Completeness, pp. 966–1021
| nopp = true
}}
* {{Cite book
| last = Sipser
| first = M.
| authorlink = Michael Sipser
| title = Introduction to the Theory of Computation
| year = 1997
| publisher = PWS Publishing
| pages = Sections 7.4–7.5 (NP-completeness, Additional NP-complete Problems), pp. 248–271
| nopp = true
| isbn = 0-534-94728-X
}}
* {{Cite book
| last = Papadimitriou
| first = C.
| authorlink = Christos Papadimitriou
| title = Computational Complexity
| edition = 1st
| year = 1994
| publisher = Addison Wesley
| pages = Chapter 9 (NP-complete problems), pp. 181–218
| isbn = 0-201-53082-1
| nopp = true
}}
* [http://www.ics.uci.edu/~eppstein/cgt/hard.html Computational Complexity of Games and Puzzles]
* [http://arxiv.org/abs/cs.CC/0210020 Tetris is Hard, Even to Approximate]
* [http://for.mat.bham.ac.uk/R.W.Kaye/minesw/ordmsw.htm Minesweeper is NP-complete!]
*{{Cite journal
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| doi = 10.1002/net.3230200110
| issue = 1
| journal = Networks
| pages = 109–120
| title = Faster exact algorithms for Steiner trees in planar networks
| volume = 20
| year = 1990
| ref = harv
| postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}}}.
*{{Cite journal
| last1 = Deĭneko | first1 = Vladimir G.
| last2 = Klinz | first2 = Bettina
| last3 = Woeginger | first3 = Gerhard J.
| doi = 10.1016/j.orl.2005.04.013
| issue = 3
| journal = Operations Research Letters
| pages = 269–274
| title = Exact algorithms for the Hamiltonian cycle problem in planar graphs
| volume = 34
| year = 2006
| ref = harv
| postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}}}.
*{{Cite book
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| last2 = Penninkx | first2 = Eelko
| last3 = Bodlaender | first3 = Hans L. | author3-link = Hans L. Bodlaender
| last4 = Fomin | first4 = Fedor V.
  | doi = 10.1007/11561071_11
| pages = 95–106
| publisher = Springer-Verlag
| series = Lecture Notes in Computer Science
| title = Proc. 13th European Symposium on Algorithms (ESA '05)
| volume = 3669
| year = 2005
| chapter = Efficient Exact Algorithms on Planar Graphs: Exploiting Sphere Cut Branch Decompositions
| isbn = 978-3-540-29118-3
| ref = harv
| postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}}}.
*{{Cite journal
| last1 = Lipton | first1 = Richard J. | author1-link = Richard J. Lipton
| last2 = Tarjan | first2 = Robert E. | author2-link = Robert Tarjan
| doi = 10.1137/0209046
| journal = [[SIAM Journal on Computing]]
| pages = 615–627
| title = Applications of a planar separator theorem
| volume = 9
| year = 1980
| issue = 3
| ref = harv
| postscript = <!-- Bot inserted parameter. Either remove it; or change its value to "." for the cite to end in a ".", as necessary. -->{{inconsistent citations}}}}.
{{refend}}
 
== Further reading ==
* [[Scott Aaronson]], ''[http://arxiv.org/abs/quant-ph/0502072 NP-complete Problems and Physical Reality]'', ACM [[SIGACT]] News, Vol. 36, No. 1. (March 2005), pp.&nbsp;30–52.
* [[Lance Fortnow]], ''[http://people.cs.uchicago.edu/~fortnow/papers/pnp-cacm.pdf The status of the P versus NP problem]'', [[Commun. ACM]], Vol. 52, No. 9. (2009), pp.&nbsp;78–86.
 
{{ComplexityClasses}}
 
{{DEFAULTSORT:Np-Complete}}
[[Category:1971 in computer science]]
[[Category:NP-complete problems| ]]
[[Category:Complexity classes]]
[[Category:Mathematical optimization]]
[[Category:Articles with inconsistent citation formats]]

Revision as of 15:19, 21 October 2013

File:P np np-complete np-hard.svg
Euler diagram for P, NP, NP-complete, and NP-hard set of problems. The left side is valid under the assumption that P≠NP, while the right side is valid under the assumption that P=NP (except that the empty language and its complement are never NP-complete)

Paediatric Surgeon Sampley from Vanderhoof, usually spends time with passions including caravaning, property developers in new industrial launch singapore and aircraft spotting. Likes to travel and have been enthused after building a journey to Biblical Tels - Megiddo.In computational complexity theory, the complexity class NP-complete (abbreviated NP-C or NPC) is a class of decision problems. A decision problem L is NP-complete if it is in the set of NP problems and also in the set of NP-hard problems. The abbreviation NP refers to "nondeterministic polynomial time."

Although any given solution to an NP-complete problem can be verified quickly (in polynomial time), there is no known efficient way to locate a solution in the first place; indeed, the most notable characteristic of NP-complete problems is that no fast solution to them is known. That is, the time required to solve the problem using any currently known algorithm increases very quickly as the size of the problem grows. This means that the time required to solve even moderately sized versions of many of these problems can easily reach into the billions or trillions of years, using any amount of computing power available today. As a consequence, determining whether or not it is possible to solve these problems quickly, called the P versus NP problem, is one of the principal unsolved problems in computer science today.

While a method for computing the solutions to NP-complete problems using a reasonable amount of time remains undiscovered, computer scientists and programmers still frequently encounter NP-complete problems. NP-complete problems are often addressed by using heuristic methods and approximation algorithms.

Formal overview

NP-complete is a subset of NP, the set of all decision problems whose solutions can be verified in polynomial time; NP may be equivalently defined as the set of decision problems that can be solved in polynomial time on a nondeterministic Turing machine. A problem p in NP is also NP-complete if every other problem in NP can be transformed into p in polynomial time. NP-complete can also be used as an adjective: problems in the class NP-complete are known as NP-complete problems.

NP-complete problems are studied because the ability to quickly verify solutions to a problem (NP) seems to correlate with the ability to quickly solve that problem (P). It is not known whether every problem in NP can be quickly solved—this is called the P = NP problem. But if any single problem in NP-complete can be solved quickly, then every problem in NP can also be quickly solved, because the definition of an NP-complete problem states that every problem in NP must be quickly reducible to every problem in NP-complete (that is, it can be reduced in polynomial time). Because of this, it is often said that the NP-complete problems are harder or more difficult than NP problems in general.

Formal definition of NP-completeness

Mining Engineer (Excluding Oil ) Truman from Alma, loves to spend time knotting, largest property developers in singapore developers in singapore and stamp collecting. Recently had a family visit to Urnes Stave Church. A decision problem C is NP-complete if:

  1. C is in NP, and
  2. Every problem in NP is reducible to C in polynomial time.

C can be shown to be in NP by demonstrating that a candidate solution to C can be verified in polynomial time.

Note that a problem satisfying condition 2 is said to be NP-hard, whether or not it satisfies condition 1.

A consequence of this definition is that if we had a polynomial time algorithm (on a UTM, or any other Turing-equivalent abstract machine) for C, we could solve all problems in NP in polynomial time.

Background

The concept of NP-completeness was introduced in 1971 by Stephen Cook in a paper entitled The complexity of theorem-proving procedures on pages 151–158 of the Proceedings of the 3rd Annual ACM Symposium on Theory of Computing, though the term NP-complete did not appear anywhere in his paper. At that computer science conference, there was a fierce debate among the computer scientists about whether NP-complete problems could be solved in polynomial time on a deterministic Turing machine. John Hopcroft brought everyone at the conference to a consensus that the question of whether NP-complete problems are solvable in polynomial time should be put off to be solved at some later date, since nobody had any formal proofs for their claims one way or the other. This is known as the question of whether P=NP.

Nobody has yet been able to determine conclusively whether NP-complete problems are in fact solvable in polynomial time, making this one of the great unsolved problems of mathematics. The Clay Mathematics Institute is offering a US $1 million reward to anyone who has a formal proof that P=NP or that P≠NP.

In the celebrated Cook-Levin theorem (independently proved by Leonid Levin), Cook proved that the Boolean satisfiability problem is NP-complete (a simpler, but still highly technical proof of this is available). In 1972, Richard Karp proved that several other problems were also NP-complete (see Karp's 21 NP-complete problems); thus there is a class of NP-complete problems (besides the Boolean satisfiability problem). Since Cook's original results, thousands of other problems have been shown to be NP-complete by reductions from other problems previously shown to be NP-complete; many of these problems are collected in Garey and Johnson's 1979 book Computers and Intractability: A Guide to the Theory of NP-Completeness.[1] For more details refer to Introduction to the Design and Analysis of Algorithms by Anany Levitin.

NP-complete problems

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File:Relative NPC chart.svg
Some NP-complete problems, indicating the reductions typically used to prove their NP-completeness

An interesting example is the graph isomorphism problem, the graph theory problem of determining whether a graph isomorphism exists between two graphs. Two graphs are isomorphic if one can be transformed into the other simply by renaming vertices. Consider these two problems:

  • Graph Isomorphism: Is graph G1 isomorphic to graph G2?
  • Subgraph Isomorphism: Is graph G1 isomorphic to a subgraph of graph G2?

The Subgraph Isomorphism problem is NP-complete. The graph isomorphism problem is suspected to be neither in P nor NP-complete, though it is in NP. This is an example of a problem that is thought to be hard, but isn't thought to be NP-complete.

The easiest way to prove that some new problem is NP-complete is first to prove that it is in NP, and then to reduce some known NP-complete problem to it. Therefore, it is useful to know a variety of NP-complete problems. The list below contains some well-known problems that are NP-complete when expressed as decision problems.

To the right is a diagram of some of the problems and the reductions typically used to prove their NP-completeness. In this diagram, an arrow from one problem to another indicates the direction of the reduction. Note that this diagram is misleading as a description of the mathematical relationship between these problems, as there exists a polynomial-time reduction between any two NP-complete problems; but it indicates where demonstrating this polynomial-time reduction has been easiest.

There is often only a small difference between a problem in P and an NP-complete problem. For example, the 3-satisfiability problem, a restriction of the boolean satisfiability problem, remains NP-complete, whereas the slightly more restricted 2-satisfiability problem is in P (specifically, NL-complete), and the slightly more general max. 2-sat. problem is again NP-complete. Determining whether a graph can be colored with 2 colors is in P, but with 3 colors is NP-complete, even when restricted to planar graphs. Determining if a graph is a cycle or is bipartite is very easy (in L), but finding a maximum bipartite or a maximum cycle subgraph is NP-complete. A solution of the knapsack problem within any fixed percentage of the optimal solution can be computed in polynomial time, but finding the optimal solution is NP-complete.

Solving NP-complete problems

At present, all known algorithms for NP-complete problems require time that is superpolynomial in the input size, and it is unknown whether there are any faster algorithms.

The following techniques can be applied to solve computational problems in general, and they often give rise to substantially faster algorithms:

  • Approximation: Instead of searching for an optimal solution, search for an "almost" optimal one.
  • Randomization: Use randomness to get a faster average running time, and allow the algorithm to fail with some small probability. Note: The Monte Carlo method is not an example of an efficient algorithm, although evolutionary approaches like Genetic algorithms may be.
  • Restriction: By restricting the structure of the input (e.g., to planar graphs), faster algorithms are usually possible.
  • Parameterization: Often there are fast algorithms if certain parameters of the input are fixed.
  • Heuristic: An algorithm that works "reasonably well" in many cases, but for which there is no proof that it is both always fast and always produces a good result. Metaheuristic approaches are often used.

One example of a heuristic algorithm is a suboptimal O(nlogn) greedy coloring algorithm used for graph coloring during the register allocation phase of some compilers, a technique called graph-coloring global register allocation. Each vertex is a variable, edges are drawn between variables which are being used at the same time, and colors indicate the register assigned to each variable. Because most RISC machines have a fairly large number of general-purpose registers, even a heuristic approach is effective for this application.

Completeness under different types of reduction

In the definition of NP-complete given above, the term reduction was used in the technical meaning of a polynomial-time many-one reduction.

Another type of reduction is polynomial-time Turing reduction. A problem X is polynomial-time Turing-reducible to a problem Y if, given a subroutine that solves Y in polynomial time, one could write a program that calls this subroutine and solves X in polynomial time. This contrasts with many-one reducibility, which has the restriction that the program can only call the subroutine once, and the return value of the subroutine must be the return value of the program.

If one defines the analogue to NP-complete with Turing reductions instead of many-one reductions, the resulting set of problems won't be smaller than NP-complete; it is an open question whether it will be any larger.

Another type of reduction that is also often used to define NP-completeness is the logarithmic-space many-one reduction which is a many-one reduction that can be computed with only a logarithmic amount of space. Since every computation that can be done in logarithmic space can also be done in polynomial time it follows that if there is a logarithmic-space many-one reduction then there is also a polynomial-time many-one reduction. This type of reduction is more refined than the more usual polynomial-time many-one reductions and it allows us to distinguish more classes such as P-complete. Whether under these types of reductions the definition of NP-complete changes is still an open problem. All currently known NP-complete problems are NP-complete under log space reductions. Indeed, all currently known NP-complete problems remain NP-complete even under much weaker reductions.[2] It is known, however, that AC0 reductions define a strictly smaller class than polynomial-time reductions.[3]

Naming

According to Donald Knuth, the name "NP-complete" was popularized by Alfred Aho, John Hopcroft and Jeffrey Ullman in their celebrated textbook "The Design and Analysis of Computer Algorithms". He reports that they introduced the change in the galley proofs for the book (from "polynomially-complete"), in accordance with the results of a poll he had conducted of the Theoretical Computer Science community.[4] Other suggestions made in the poll[5] included "Herculean", "formidable", Steiglitz's "hard-boiled" in honor of Cook, and Shen Lin's acronym "PET", which stood for "probably exponential time", but depending on which way the P versus NP problem went, could stand for "provably exponential time" or "previously exponential time".[6]

Common misconceptions

The following misconceptions are frequent.[7]

  • "NP-complete problems are the most difficult known problems." Since NP-complete problems are in NP, their running time is at most exponential. However, some problems provably require more time, for example Presburger arithmetic.
  • "NP-complete problems are difficult because there are so many different solutions." On the one hand, there are many problems that have a solution space just as large, but can be solved in polynomial time (for example minimum spanning tree). On the other hand, there are NP-problems with at most one solution that are NP-hard under randomized polynomial-time reduction (see Valiant–Vazirani theorem).
  • "Solving NP-complete problems requires exponential time." First, this would imply P ≠ NP, which is still an unsolved question. Further, some NP-complete problems actually have algorithms running in superpolynomial, but subexponential time. For example, the Independent set and Dominating set problems are NP-complete when restricted to planar graphs, but can be solved in subexponential time on planar graphs using the planar separator theorem.[8]
  • "All instances of an NP-complete problem are difficult." Often some instances, or even most instances, may be easy to solve within polynomial time. However, unless P=NP, any polynomial-time algorithm must asymptotically be wrong on more than polynomially many of the exponentially many inputs of a certain size.[9]
  • "If P=NP, all cryptographic ciphers can be broken." A polynomial-time problem can be very difficult to solve in practice if the polynomial's degree or constants are large enough. For example, ciphers with a fixed key length, such as Advanced Encryption Standard, can all be broken in constant time (and are thus already in P), though that constant may exceed the age of the universe.

See also

Notes

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References

Template:Refbegin

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  • 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.

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  • 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.

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  • Computational Complexity of Games and Puzzles
  • Tetris is Hard, Even to Approximate
  • Minesweeper is NP-complete!
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

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    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

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    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

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    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

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    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang.
  • 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.
  • One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang.

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  1. 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.

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  2. One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  3. One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
  4. Don Knuth, Tracy Larrabee, and Paul M. Roberts, Mathematical Writing § 25, MAA Notes No. 14, MAA, 1989 (also Stanford Technical Report, 1987).
  5. One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting

    In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang

    Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules

    Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.

    A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running

    The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more

    There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang
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