Questions tagged [cc.complexity-theory]

P versus NP and other resource-bounded computation.

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43 votes
7 answers
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Many-one reductions vs. Turing reductions to define NPC

Why do most people prefer to use many-one reductions to define NP-completeness instead of, for instance, Turing reductions?
Matthias's user avatar
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22 votes
2 answers
604 views

Lower bounds for constant-depth formulae?

We know a lot about the limitations of (polynomial size) constant-depth circuits. Since (polynomial size) constant-depth formulae are an even more restricted model of computation, all problems known ...
Robin Kothari's user avatar
21 votes
3 answers
543 views

Are recursive forms of Godel's statement possible?

The self-referentiality of the P/NP problem has sometimes been highlighted as a barrier to its resolution, see, for instance, Scott Aaronson's paper, is P vs. NP formally independent? One of the many ...
Anand Kulkarni's user avatar
36 votes
5 answers
2k views

Complexity of testing for a value versus computing a function

In general we know that the complexity of testing whether a function takes a particular value at a given input is easier than evaluating the function at that input. For example: Evaluating the ...
Joshua Grochow's user avatar
51 votes
4 answers
5k views

What are the best current lower bounds on 3SAT?

What are the best current lower bounds for time and circuit depth for 3SAT?
Joe Fitzsimons's user avatar
24 votes
2 answers
897 views

What evidence do we have for (and against) Unique Games Conjecture?

Subhash Khot's Unique Games Conjecture is one of active research areas in complexity theory. What evidence do we have for it? What evidence do we have against it?
21 votes
4 answers
505 views

Which results in complexity theory make essential use of uniformity?

A complexity class separation proof uses uniformity of complexity classes essentially if the proof does not prove the result for nonuniform version, for example proofs based on diagonalization (like ...
Kaveh's user avatar
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141 votes
30 answers
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Problems Between P and NPC

Factoring and graph isomorphism are problems in NP that are not known to be in P nor to be NP-Complete. What are some other (sufficiently different) natural problems that share this property? ...
17 votes
2 answers
696 views

H-free cut problem

Suppose you are given a connected, simple, undirected graph H. The H-free cut problem is defined as follows: Given a simple, undirected graph G, is there a cut (partition of vertices into two ...
Aryabhata's user avatar
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27 votes
4 answers
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What specific evidence is there for P = RP?

RP is the class of problems decidable by a nondeterministic Turing machine that terminates in polynomial time, but that is also allowed one-sided error. P is the usual class of problems decidable by ...
András Salamon's user avatar
30 votes
2 answers
2k views

Hierarchies in NP (under the assumption that P != NP)

Assuming that P != NP, I believe it has been shown that there are problems which are not in P and not NP-Complete. Graph Isomorphism is conjectured to be such a problem. Is there any evidence of more ...
Aryabhata's user avatar
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27 votes
1 answer
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Consequences of Complete problems for NP intersects coNP

What are the consequences of having complete problems in $NP\cap coNP$?
Marcos Villagra's user avatar
65 votes
11 answers
5k views

What are good references to understanding the proof of the PCP theorem?

I'm familiar with a lot of results that use the PCP theorem (mainly in approximating algorithms), but I've never come across a clear explanation of the PCP theorem (ie, that $\mathsf{NP} = \mathsf{PCP}...
Alexandre Passos's user avatar
25 votes
3 answers
1k views

Graph Isomorphism and hidden subgroups

I'm trying to understand the relationship between graph isomorphism and the hidden subgroup problem. Is there a good reference for this ?
Suresh Venkat's user avatar
35 votes
4 answers
1k views

Correspondence between complexity classes and logic

I took a class once on Computability and Logic. The material included a correlation between complexity / computability classes (R, RE, co-RE, P, NP, Logspace, ...) and Logics (Predicate calculus, ...
ripper234's user avatar
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8 votes
3 answers
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Is Deolalikar's 2010 proof that $P \ne NP$ correct?

There was recently a claimed proof that $P \ne NP$. Not long after its publication there were raised some issues with this proof. So ... is the proof correct or not ? (Please only answer this if you ...
ripper234's user avatar
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21 votes
3 answers
579 views

space-bounded TMs and oracles

In general, the query-tape for an oracle counts towards the space-complexity of a TM. However, it seems plausible to allow a write-only oracle-tape (such as is used in L-space reductions). Is such a ...
Jeremy Hurwitz's user avatar
15 votes
2 answers
1k views

What is the following variation on Set Cover known as?

What is the following variation on set cover known as? Given a set S, a collection C of subsets of S and a positive integer K, do there exist K sets in C such that every pair of elements of S lies in ...
deinst's user avatar
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