Questions tagged [complexity-classes]

Computational complexity classes and their relations

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Semantic vs. Syntactic Complexity Classes

In his "Computational Complexity" book, Papadimitriou writes: RP is in some sense a new and unusual kind of complexity class. Not any polynomially bounded nondeterministic Turing machine can be the ...
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NEXP-complete problems

There are tons of NP-complete problems around and sources collecting them, e.g. see the book by Garey and Johnson. I would be interested to see a list of NEXP-complete problems as well. Is there one ...
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1 answer
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Looking for a nice problem inside SC but not in the first two levels

The complexity zoo doesn't have much about the $\mathsf{SC}$. I am looking for a nice$^\dagger$ problem that is in higher levels of the hierarchy, i.e. a problem in $\mathsf{DTimeSpace}(n^{O(1)},\lg^{...
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Can one amplify P=NP beyond P=PH?

In Descriptive Complexity, Immerman has Corollary 7.23. The following conditions are equivalent: 1. P = NP. 2. Over finite, ordered structures, FO(LFP) = SO. This can be thought of as "...
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38 votes
3 answers
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Does $VP \neq VNP$ imply $P \neq NP$?

As far as I understand, the geometric complexity theory program attempts to separate $VP \neq VNP$ by proving that the permament of a complex-valued matrix is much harder to compute than the ...
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Is NP in $DTIME(n^{poly\log n})$?

Is NP in $DTIME(n^{poly\log n})$?
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Consequences of UP equals NP

EDIT at 2011/02/08: After some references finding and reading, I decided to separate the original question into two separate ones. Here's the part concerning UP vs NP, for the syntactic and semantic ...
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Problem in BPP but not known to be in RP or co-RP

Is there an example of a natural problem that's in BPP but that's not known to be in RP or co-RP?
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Do all complexity classes have a leaf language characterization?

Leaf languages are a beautiful way to uniformly define many complexity classes. Most complexity classes are usually specified by a model of computation (e.g., deterministic/randomized TM), and a ...
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Is $coNP^{\#P}=NP^{\#P}=P^{\#P}$?

By http://www.cs.umd.edu/~jkatz/complexity/relativization.pdf If $A$ is a PSPACE-complete language, $P^{A}=NP^{A}$. If $B$ is a deterministic polynomial-time oracle, $P^{B}\ne NP^{B}$ (assuming $P\...
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What is the complexity class most closely associated with what the human mind can accomplish quickly?

This question is something I've wondered about for a while. When people describe the P vs. NP problem, they often compare the class NP to creativity. They note that composing a Mozart-quality ...
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Examples where the uniqueness of the solution makes it easier to find

The complexity class $\mathsf{UP}$ consists of those $\mathsf{NP}$-problems that can be decided by a polynomial time nondeterministic Turing machine which has at most one accepting computational path. ...
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What are the consequences of Parity-L = P?

Parity-L is the set of languages recognized by a non-deterministic Turing machine which can only distinguish between an even number or odd number of "acceptance" paths (rather than a zero or ...
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Problems outside of P that are not P-hard

While reading an answer by Peter Shor and an earlier question by Adam Crume I realized that I have some misconceptions about what it means to be $\mathsf{P}$-hard. A problem is $\mathsf{P}$-hard if ...
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Is there a better than linear lower bound for factoring and discrete log?

Are there any references that provide details about circuit lower bounds for specific hard problems arising in cryptography such as integer factoring, prime/composite discrete logarithm problem and ...
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Benefits for syntactic and semantic classes

This is a post separated from Consequences of UP equals NP, and also a follow-up question to Semantic vs. Syntactic Complexity Classes. In the above post we learned about the semantic and syntactic ...
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Natural candidate against the Isomorphism Conjecture?

The famous Isomorphism Conjecture of Berman and Hartmanis says that all $NP$-complete languages are polynomial time isomorphic (p-isomorphic) to each other. The key significance of the conjecture is ...
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Is there a PSPACE-intermediate language?

Suppose PH is strictly contained in PSPACE. Is there a problem in PSPACE that is not in PH and not PSPACE-complete? I encountered a language that is in PSPACE. The question is whether it's in PH. So ...
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XOR-SAT to Horn-SAT reduction

Horn-SAT (conjunction of Horn clauses) is P-complete and XOR-SAT (conjunction of xor clauses) is in P. This means that there is a reduction from XOR-SAT to Horn-SAT weaker than a polynomial reduction. ...
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230 votes
11 answers
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Is Norbert Blum's 2017 proof that $P \ne NP$ correct?

Norbert Blum recently posted a 38-page proof that $P \ne NP$. Is it correct? Also on topic: where else (on the internet) is its correctness being discussed? Note: the focus of this question text has ...
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35 votes
3 answers
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An Anthology of Complexity Assumptions

In the paper The Random Oracle Hypothesis Is False, the authors (Chang, Chor, Goldreich, Hartmanis, Håstad, Ranjan, and Rohatgi) discuss the implications of the random-oracle hypothesis. They argue ...
39 votes
7 answers
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What do we know about provably correct programs?

The ever increasing complexity of computer programs and the increasingly crucial position computers have in our society leaves me wondering why we still don't collectively use programming languages in ...
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25 votes
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Hardness of approximation - additive error

There is a rich literature and at least one very good book setting out the known hardness of approximation results for NP-hard problems in the context of multiplicative error (e.g. 2-approximation for ...
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What are the consequences of $\mathsf{L}^2 \subseteq \mathsf{P}$?

We know that $\mathsf{L} \subseteq \mathsf{NL} \subseteq \mathsf{P}$ and that $\mathsf{L} \subseteq \mathsf{NL} \subseteq \mathsf{L}^2 \subseteq $ $\mathsf{polyL}$, where $\mathsf{L}^2 = \mathsf{...
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Succinct Problems in $\mathsf{P}$

The study of Succinct representation of graphs was initiated by Galperin and Wigderson in a paper from 1983, where they prove that for many simple problems like finding a triangle in a graph, the ...
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Consequences of NP=PSPACE

What would be the nasty consequences of NP=PSPACE? I am surprised I did not found anything on this, given that these classes are among the most famous ones. In particular, would it have any ...
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Why do equalities between complexity classes translate upwards and not downwards?

Hey Guys, I understand that the padding trick allows us to translate complexity classes upwards - for example $P=NP \rightarrow EXP=NEXP$. Padding works by "inflating" the input, running the ...
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What are the relationships between those hypotheses in Fine-Grained Complexity Theory?

Complexity theory, through such concepts as NP-completeness, distinguishes between computational problems that have relatively efficient solutions and those that are intractable. "Fine-grained" ...
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21 votes
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Limits to Parallel Computing

I am curious in a broad sense about what is known about parallelizing algorithms in P. I found the following wikipedia article about the subject: http://en.wikipedia.org/wiki/NC_%28complexity%29 The ...
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4 answers
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Parity and $AC^0$

Parity and $AC^0$ are like inseparable twins. Or so it has seemed for the last 30 years. In the light of Ryan's result, there will be renewed interest in the small classes. Furst Saxe Sipser to Yao ...
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Does diagonalization captures the essence of class separation ?

I don't remember having seen a class separation not based on diagonalization and relativization results. Diagonalization could still be used to separate remaining known classes, because non-...
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1 answer
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Time Hierarchies in DSPACE(O(s(n)))

The time hierarchy theorem states that turing machines can solve more problems if they have (enough) more time. Does it hold in some way if the space is limited asymptotically? How does $\textrm{DTISP}...
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What is the big version of NC?

$\mathsf{NC}$ captures the idea of efficiently parallelizable, and one interpretation of it is problems that are solvable in time $O(\log^c n)$ using $O(n^k)$ parallel processors for some constants $c$...
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14 votes
1 answer
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Problems in NC not known to lie in NC2

Are there interesting problems that are in $\mathsf{NC}$ but not known to be in $\mathsf{NC^{2}}$? In the paper 'A Taxonomy of Problems With Fast Parallel Algorithms', Cook mentions that MIS was known ...
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What are the compelling reasons for believing $L\neq P$?

What are the compelling reasons for believing $L\neq P$? L is the class of log-space algorithms with pointers to the input. Suppose L=P for the moment. What would a log-space algorithm for a P-...
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1 answer
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Cutting-sticks puzzle

Problem: We are given a set of sticks all having integer lengths. The total sum of their lengths is n(n+1)/2. Can we break them up to get sticks of size ${1,2,\ldots,n}$ in polynomial time? ...
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Reducing #SAT to #MONOTONE-2SAT

The problem #MONOTONE-2SAT is known to be #P-complete. This means that #SAT can be reduced to it. My question is: given a #SAT instance $F$, which is the transformation that converts $F$ to its ...
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15 votes
2 answers
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Quantum analogues of SPACE complexity classes

We often consider complexity classes where we are bounded in the amount of space our Turing machine can use, for example: $\textbf{DSPACE}(f(n))$ or $\textbf{NSPACE}(f(n))$. It seems that early in ...
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1 answer
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Is Quasi-polynomial time in PSPACE?

I had done some search on this but I was not able to find an answer either way. Huck answered it fully. Thanks :)
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Intuition for the UP class

UP class is defined as such: The class of decision problems solvable by an NP machine such that If the answer is 'yes,' exactly one computation path accepts. If the answer is 'no,' all ...
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What evidence do we have for $\mathsf{UP} \neq \mathsf{NP}$?

Following Josh Grochow's suggestion, I am converting my comment from a previous question into a new question. What evidence do we have for $\mathsf{UP} \neq \mathsf{NP}$? Here $\mathsf{UP}$ is the ...
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An analog of DP for the second level of the polynomial hierarchy

The complexity class DP can be defined as the set of all languages that are the intersection of an NP language with a coNP language. I have a language for which I wish to determine the exact ...
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Is $(NP^{NP})^{NP} = NP^{(NP^{NP})}$?

In the "last paragraph" of the "first page" of the following paper: Vikraman Arvind, Johannes Köbler, Uwe Schöning, Rainer Schuler, "If NP Has Polynomial-Size Circuits, then MA = AM," Theoretical ...
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8 votes
1 answer
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Are there more polynomial time problems with complexity lower bounds?

I'm looking for more problems in $P$ with classical time complexity lower bounds. Some people might wonder how you could prove such a lower bound. See below. Exponential Lower Bounds: Claim: If ...
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10 votes
1 answer
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A natural problem in $\textrm{S}_2^\textrm{P}$?

The complexity class $\textrm{S}_2^\textrm{P}$ is defined as follows (from Wikipedia): A language $L$ is in $S_2^P$ if there exists a polynomial-time predicate $P$ such that If $x \in L$, ...
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2 answers
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For which values of $k$ is the $k$-disjoint paths problem in $\mathcal{P}$?

The $k$-Vertex-Disjoint Paths Problem ($k$-$\text{DPP}$) is defined as follows: Input: A graph $G=(V,E)$ and $k$ pairs of vertices $(s_1,t_1),\ldots,(s_k,t_k)$. Question: Does there exist $k$-...
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36 votes
8 answers
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Problems with big open complexity gaps

This question is about problems for which there is a big open complexity gap between known lower bound and upper bound, but not because of open problems on complexity classes themselves. To be more ...
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23 votes
6 answers
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Statements that imply $\mathbf{P}\neq \mathbf{NP}$

This is sort of an open-ended question - for which I apologize in advance. Are there examples of statements that (seemingly) don't have anything to do with complexity or Turing machines but the ...
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34 votes
3 answers
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complexity of greatest common divisor (gcd)

Consider the following counting problem (or the associated decision problem): Given two positive integers encoded in binary, compute their greatest common divisor (gcd). What is the smallest ...
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26 votes
3 answers
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Consequences of #P = FP

Which would be the consequences of #P = FP? I'm interested in both practical and theoretical consequences. From a practical point of view, I'm particularly interested in consequences on Artificial ...
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