Questions tagged [cc.complexity-theory]

P versus NP and other resource-bounded computation.

2
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0answers
27 views

Example of a hardness-of-approximation proof which improves the approximation factor?

Are there any examples of hardness-of-approximation reductions where we get a better hardness bound for the problem we've reduced to than the problem we've reduced from? In the examples I've seen so ...
6
votes
0answers
118 views

Planar Exact Cover by even-size sets

Major edit on June 6, 2019: Replaced the target problem with a simpler (but equivalent) one. Is the following problem NP-complete? Planar Exact Cover by even-size sets Input: A set $U$, a ...
1
vote
1answer
104 views

Count satisfying assignments of CNF formulas over all possible negation assignments

Consider the set of all CNF instances that can be generated by adding negations to a single monotone CNF instance. How hard is it to compute the sum of the counts of satisfying assignments for the set?...
0
votes
0answers
78 views

Is it possible to sort by only knowing the sign of pairwise sums?

I am currently thinking of how much structure one actually needs in order to be able to sort things at all. All comparison-based algorithms need a direct comparability, but are we able to remove this ...
2
votes
0answers
79 views

Is $MSB$ of permanent and certifying half number of witnesses easy?

Can there be a $P$ algorithm to decide if number of perfect matchings is at least $(n!/2)+1$ for a bipartite graph on $n+n$ vertices? Can there be a $P$ algorithm to decide if number of witnesses ...
2
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0answers
34 views

Problem of determining if a $4$ connected graph has $k$ Hamiltonian cycles

Definition: Define the $k$-HamiltonianCycles problem as the decision problem that asks if a given graph has at least $k$ distinct Hamiltonian cycles. Question: Is there some constant $k$ so that the $...
-6
votes
0answers
108 views

$n^2 x n^2$ Sudoku Puzzles have equal amount of easy-instances that can be solved in $O(n^k)$ time, under experimentation so far this is correct

Introduction I found out that I can take any $n^2 x n^2$ puzzle, solve it and study its permutation pattern and implement it into a poly-time Sudoku Generator. I also found out that a limited subset ...
13
votes
2answers
1k views

Oblivious Turing Machine emulation lower bound

Is there a proof that the emulation of a Turing machine on an oblivious Turing machine can't be done in less than $\mathcal{O}\left(m\log m\right)$ where $m$ is the number of steps the Turing machine ...
6
votes
2answers
366 views

Is this partition problem strongly NP-complete?

Some computational problems have variants that appear to be harder. For instance, Graph Automorphism (GA) problem has quasi-polynomial time algorithm ( by Babai's Graph Isomorphism result) while the ...
4
votes
3answers
246 views

Variation on partial Set Cover with penalties

I'm looking at the following problem, which I'm hoping is perhaps a known variant of the Set Cover problem: Input: We're given a universe $U$ and two disjoint subsets $A$ and $B$ such that $A \cup B=...
4
votes
2answers
753 views

Attempted proofs of P vs NP

What are the most recent (say in the last 3 years) attempts at disproving $P = NP$, and where can I find the papers?
3
votes
0answers
97 views

Razborov-Smolensky polynomial argument on $\textrm{ACC}[q]$ where $q$ is a prime power

It seems to be a folklore that we can "handle" $\textrm{ACC}[q]$ circuits not only for prime $q$ but prime power $q$. For example, authors of this paper say that ... any constant depth circuit ...
1
vote
0answers
51 views

Graph automorphism with prescribed values

Consider a graph $G$ with vertices labeled $1,...,n$ and edge weights $w_{ij}$. Recall an automorphism of G is a permutation $\sigma$ of the vertex labels such that $w_{\sigma(i),\sigma(j)}=w_{ij}$ ...
1
vote
1answer
106 views

Is the unbounded fan-in model realistic?

Does the unbounded fan-in circuit model apply in "practical" settings? In other words, are there real-world realisable computers with unbounded fan-in gates? As I understand, standard silicon ASICs ...
4
votes
1answer
164 views

Which (almost) balanced Boolean function has smallest “total” influence

The well known Kahn–Kalai–Linial (KKL) Theorem says that for any Boolean function $f\colon \{-1,1\}^n \xrightarrow{} \{-1,1\}$ $$ \max_{i \in [n]} \{\mathbf{Inf}_i[f] \} \geq \mathop{\bf Var}[f] \cdot ...
1
vote
0answers
119 views

Can a hash preimage be used to amplify BPP probabilities?

Suppose we have an algorithm in $\mathrm{BPP}$ to decide membership in a language $L$. Normally we amplify the probability of accepting and rejecting members correctly by running our algorithm ...
-1
votes
0answers
62 views

Validity of relativization argument

In the book 'Computational complexity' by Arora-Barak, I was studying that any result of TM/ complexity classes that use only the following two properties of TM's are called relativizing results : $I....
2
votes
2answers
192 views

Under what models do we know linear time sorting?

The best we know for general case sorting is $O(n\log n)$ (which is also $\theta(n\log n)$ is decision tree model) and the problem of $O(n)$ sorting is open for turing machine models. Under what ...
11
votes
1answer
540 views

Technical issue with PCP theorem proof

I am reading the proof from here and I stumbled upon a technical (yet crucial) problem. I know this is rather specific and the context is problematic, but I couldn't figure it out myself. In pages 51 ...
8
votes
1answer
251 views

Is there any quantum analog of the VP vs. VNP problem?

From Wikipedia: $\mathsf{VP}$: The class VP is the algebraic analog of P; it is the class of polynomials $f$ of polynomial degree that have polynomial size circuits over a fixed field $K$. $\...
-1
votes
1answer
84 views

Comprehensive list of functions used in Big-$O$ notation

We all know that exponential functions grow faster than polynomials. Let us consider the following function: $f(n)=n^{a_1}⋅(\log n)^{a_2}⋅(\log\log n)^{a_3}⋅(\log\log\log n)^{a_4}⋯ $ where the leading ...
-1
votes
0answers
17 views

How to deal with tradeoffs while making choices?

Sometimes while writing some code I make some decisions, the "problem" is that every choice has a negative consequence. Is coming with the perfect architecture possible? You'll tell me; perfect ...
8
votes
3answers
389 views

Why exactly are complexity theorists interested in closed timelike curves?

Context: There are several papers that study the implications of closed timelike curves (CTCs) to quantum complexity. In 2008, Aaronson and Watrous published their famous paper on this topic which ...
30
votes
6answers
2k views

Is there a natural problem on the naturals that is NP-complete?

Any natural number can be regarded as a bit sequence, so inputting a natural number is the same as inputting a 0-1 sequence, so NP-complete problems with natural inputs obviously exist. But are there ...
20
votes
1answer
394 views

Is prime-counting function #P-complete?

Recall $\pi(n)$ the number of primes $\le n$ is the prime-counting function. By "PRIMES in P", computing $\pi(n)$ is in #P. Is the problem #P-complete? Or, perhaps, there is a complexity reason to ...
4
votes
1answer
153 views

Why is counting the number of hamiltonian subgraphs $\sharp P $ hard?

I'm confused about how to prove either of the following closely related statements. They are both from this paper: https://epubs.siam.org/doi/10.1137/0208032 1) "A further problem that can be shown ...
3
votes
0answers
215 views

Convention for RAM machine models

When algorithm asymptotic runtimes are given without explicitly noting the computational model, what is the convention for the exact model used? My understanding is that most problems use unit-cost ...
2
votes
0answers
56 views

$XP_{\text{uniform}}=FPT$ and update to $EPTAS$ section in complexity zoo?

Complexity zoo in https://complexityzoo.uwaterloo.ca/Complexity_Zoo:E#eptas has the following: $FPT = XPuniform\implies EPTAS = PTAS$. Fundamentals of Parametrized complexity on page $534$ has ...
2
votes
0answers
132 views

Is the following problem in $coNP$?

Given an $n\times n$ matrix $M$ with $\mathbb Z$ entries is 'does an $\frac n2\times\frac n2$ minor of $M$ vanish?' in $\bf{coNP}$? At least one $\frac n2\times\frac n2$ minor non-vanish implies rank ...
0
votes
0answers
43 views

What is the complexity of Parametric Mixed Integer Linear Programming?

We know $$\forall\bf y\in\mathbb Z^n:K\bf y\leq b$$ $$\exists\bf x\in\mathbb Z^m:A\bf x + B\bf y\leq c$$ is in $\bf P$ if $n,m$ are fixed from Kannan's result (refer page $1$ in reference). What is ...
2
votes
1answer
118 views

Lower bound on alternations needed in $BQP$ versus $PH$ result?

What is the fastest $f(n)$ the relatively new result of oracle separation of $\mathsf{BQP}$ from $\mathsf{PH}$ provides such that ${\#\mathsf{SAT}}\not\subseteq\mathsf{FP}^{\mathsf{PH}[O(f(n))]}$ ...
15
votes
1answer
1k views

What's the status of Babai's Graph isomorphism result?

It's been over a year since his January 2017 retraction and correction. Is there news? If not is this normal for validation to take this long? I would expect it would get plenty of attention. Has ...
10
votes
1answer
350 views

An obstruction like ETH

We know under $ETH$ we cannot solve $K$-SUM in $f(K)poly(nK)$ time under any function $f(K)$ (usually $2^{O(K)}$). Is there any conjecture that prevents a $(\log n)^{O(K)}$ complexity (this is ...
2
votes
1answer
65 views

Hardness of LWE on not-uniform vector samples

The "usual decisional LWE": The challenger and the adversary get a common random matrix $A \in F_{q}^{m \times n}$. The challenger chooses a secret $s \in F_{q}^{n}$ and generates random (small) ...
-1
votes
1answer
80 views

Why is $BPP^{NP}$ in polynomial hierarchy? [closed]

Why is $BPP^{NP}$ in the polynomial hierarchy? I know that $BPP$ is contained in $NP^{NP}$, so $BPP$ is inside $PH$. However, how does that imply $BPP^{NP}$ is inside the polynomial hierarchy?
2
votes
1answer
112 views

How to use a 𝑝-coin so a TM can decide an undecidable language in polynomial time? [closed]

In "Computational complexity- A modern approach" book (page 117) for the lemma 7.12 (following) the author mentioned that if the ρ is efficiently computable ρ-coin cannot give probabilistic algorithm ...
10
votes
1answer
285 views

How hard is deciding the existence of Red-Blue perfect matching?

Two-colorable perfect matching problem is to decide whether a graph has coloring with two colors such that each node has exactly one neighbor the same color as itself. The problem was proven to be NP-...
2
votes
0answers
112 views

A complexity-class of problems that cannot be solved in finite time

Consider the following game: Alice chooses a real function number $x\in [0,1]$; Bob has to guess the number by asking Alice any number of queries of the form "is $x > a$?" [where Bob can choose ...
17
votes
4answers
2k views

Is there a natural problem in quasi-polynomial time, but not in polynomial time?

László Babai recently proved that the Graph Isomorphism problem is in quasipolynomial time. See also his talk at University of Chicago, note from the talks by Jeremy Kun GLL post 1, GLL post 2, GLL ...
11
votes
0answers
153 views

$\exists \mathbb R$ and IP

We know NP$\subseteq$ $\exists \mathbb R$$\subseteq$ PSPACE=IP, but is there some more direct proof for $\exists \mathbb R\subseteq$ IP? What about the other direction, are there some Arthur-Merlin ...
1
vote
0answers
73 views

Minimum cut with nonlinear objective function

Let $G$ be an undirected graph. The classic minimum (cardinality) cut problem asks for a cut $C\subseteq E(G)$, such that $|C|$ is minimum. Let us generalize it the following way: let $f$ be a ...
3
votes
0answers
82 views

Counting quotient graphs, but not exactly

All graphs considered will be directed graphs $G=(V,E)$, with $E \subseteq V \times V$ (so possibly with self-loops). For $k \in \mathbb{N}_{\geq 1}$, I will write $[k]$ the set $\{1,\ldots,k\}$. A $k$...
29
votes
1answer
2k views

Fourier coefficients Boolean Functions described by Bounded Depth Circuits with AND OR and XOR gates

Let $f$ be a Boolean function and let's think about f as a function from $\{-1,1\}^n$ to $\{ -1,1 \}$. In this language the Fourier expansion of f is simply the expansion of f in terms of square free ...
1
vote
1answer
145 views

Is balanced Hamiltonian cycle NP complete on maximal plane graphs?

I know that the Hamiltonian cycle is NP complete on the class of maximal plane graphs. If we instead ask about balanced Hamiltonian cycles (i.e. same number of faces on both sides) on maximal plane ...
1
vote
1answer
142 views

Does Hadwiger conjecture imply that NP = coNP?

(Disclaimer: I suspect the answer is no, but I fail to see why) Here is a nice picture by David Epstein (taken from Wikipedia) illustrating Hadwiger's conjecture: The point is that if in a given ...
1
vote
0answers
111 views

Canonical complete problem for $\mathrm{FP}^{\Sigma^p_2}$

Given a $\Sigma^p_2$-complete oracle (i.e., $\Sigma_2 \mathrm{SAT}$), I have a problem that requires to call this oracle polynomially many times and returns an integer. Essentially, this is a function ...
2
votes
0answers
48 views

Complexity of comparing extended integer power towers

Inspired by this stackexchange question, is it an open problem to compare two power towers of positive integers if we additionally allow numbers lower in the tower to themselves be represented by ...
3
votes
1answer
130 views

How small can extension complexity be?

In this article on extension complexity of regular polygons https://arxiv.org/pdf/1505.08031.pdf it is mentioned that extension complexity of $n$ regular polygons should be $\theta(\log n)$. This is ...
1
vote
1answer
59 views

Complexity status of the Edge Deletion problem to bounded degree graphs

I'm interested in the complexity status of the following problem. Input: a graph $G=(V,E)$ and two natural numbers $k$ and $d$. Output: Yes, if there exists a subset $E' \subseteq E$ of cardinality ...
2
votes
2answers
510 views

Strongly NP-complete variants of subset sum or partition problem

Some problems have variants that appear to be harder. For instance, Graph Automorphism (GA) problem has quasi-polynomial time algorithm ( by Babai's GI result). However, the fixed-point free GA ...