Examples of using Polynomial-time in English and their translations into Serbian
{-}
-
Colloquial
-
Ecclesiastic
-
Computer
-
Latin
-
Cyrillic
Another generalization of P is P/poly, or Nonuniform Polynomial-Time.
For complexity classes larger than P, polynomial-time reductions are commonly used.
If there is a polynomial-time algorithm for even one of them, then there is a polynomial-time algorithm for all the problems in NP.
Although it is widely suspected that there are no polynomial-time algorithms for these problems, this has never been proven.
When studying the complexity class NP andharder classes such as the polynomial hierarchy, polynomial-time reductions are used.
This is because a polynomial-time solution to Π1 would yield a polynomial-time solution to Π2.
Because of the many important problems in this class,there have been extensive efforts to find polynomial-time algorithms for problems in NP.
This is due to the fact that a polynomial-time solution to Π1 would yield a polynomial-time solution to Π2.
Because the problem is not solved, being able to reduce to known NP-complete problem, Π 2, to another problem,Π 1would not know polynomial-time solution for Π 1.
Some problems are known to be solvable in polynomial-time, but no concrete algorithm is known for solving them.
This algorithm can be derandomized with the method of conditional probabilities;therefore there is a simple deterministic polynomial-time 0.5-approximation algorithm as well.
In other words, there is a polynomial-time algorithm that transforms instances of one to instances of the other with the same answer.
Because the problem P= NP is not solved, being able to reduce another problem, Π1, to a known NP-complete problem, Π2,would indicate that there is no known polynomial-time solution for Π1.
It is not, however, known orbelieved to be equal to RLP or ZPLP, the polynomial-time restrictions of RL and ZPL which some authors refer to as RL and ZPL.
A polynomial-time reduction proves that the first problem is no more difficult than the second one, because whenever an efficient algorithm exists for the second problem, one exists for the first problem as well.
The problem of counting the number of isomorphisms between two graphs is polynomial-time equivalent to the problem of telling whether even one exists.
A polynomial-time Turing reduction from a problem A to a problem B is an algorithm that solves problem A using a polynomial number of calls to a subroutine for problem B, and polynomial time outside of those subroutine calls.
The Max-Cut Problem is APX-hard,meaning that there is no polynomial-time approximation scheme(PTAS), arbitrarily close to the optimal solution, for it, unless P= NP.
There are many different types of reductions, based on the method of reduction, such as Cook reductions, Karp reductions and Levin reductions, and the bound on the complexity of reductions,such as polynomial-time reductions or log-space reductions.
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.
Since the aforementioned decision problem for CSG's is PSPACE-complete,that makes them totally unworkable for practical use, as a polynomial-time algorithm for a PSPACE-complete problem would imply P=NP.
Therefore, for complexity classes within P such as L, NL, NC,and P itself, polynomial-time reductions cannot be used to define complete languages: if they were used in this way, every nontrivial problem in P would be complete.
Thus the class of NP-complete problems contains the most difficult problems in NP, in the sense that they are the ones most likely not to be in P. Because the problem P= NP is not solved, being able to reduce a known NP-complete problem, Π2, to another problem, Π1,would indicate that there is no known polynomial-time solution for Π1.
The most frequently used of these are the many-one reductions, andin some cases the phrase"polynomial-time reduction" may be used to mean a polynomial-time many-one reduction.
A polynomial-time many-one reduction from a problem A to a problem B(both of which are usually required to be decision problems) is a polynomial-time algorithm for transforming inputs to problem A into inputs to problem B, such that the transformed problem has the same output as the original problem.
For instance, given a context-free grammar, one can use the Chomsky normal form to construct a polynomial-time algorithm that decides whether a given string is in the language represented by that grammar or not(the CYK algorithm).
For instance, if a problem X can be solved using an algorithm for Y, X is no more difficult than Y, and we say that X reduces to Y. There are many different types of reductions, based on the method of reduction, such as Cook reductions, Karp reductions and Levin reductions, and the bound on the complexity of reductions,such as polynomial-time reductions or log-space reductions.
If in fact the graph isomorphism problem is solvable in polynomial time, GI would equal P. As is common for complexity classes within the polynomial time hierarchy, a problem is called GI-hard if there is apolynomial-time Turing reduction from any problem in GI to that problem, i.e., a polynomial-time solution to a GI-hard problem would yield a polynomial-time solution to the graph isomorphism problem(and so all problems in GI).
For his continuing contributions to the theory of algorithms including the development of efficient algorithms for network flow and other combinatorial optimization problems,the identification of polynomial-time computability with the intuitive notion of algorithmic efficiency, and, most notably, contributions to the theory of NP-completeness.