Questions tagged [reductions]

A reduction is the transformation of one problem into another problem. A example of using a reduction would be to be to show if a problem P is undecidable. This would be achieved by transforming or performing a reduction of a decision problem $P$ into an undecidable problem. If this can be achieved then we have shown that this problem P is undecidable.

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Can a NEXP machine simulate invalid queries to a promise problem oracle?

Let $A=(A_{YES},A_{NO})$ be some promise problem (such as xSAT, the Local Hamiltonian problem, etc). Suppose we want to show that a P machine with access to a the oracle A can always have its output ...
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Why is the reduction from 3-SAT to 3-dimensional Matching Parsimonious?

In this talk at the Simons Institute, Holger Dell notes that there is a parsimonious reduction from 3-SAT to the 3-dimensional Matching (3-DM) problem. In other words, there is a reduction between ...
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Is the knapsack variant with small profit and unlimited repetition of items NP-hard?

Consider the unbounded Knapsack problem where we are given $n$ items of integral weights $w_i$, integral profits $p_i$, and a max weight $W$. The goal is to maximize the total profit $\sum_i x_ip_i$ ...
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Existing implementation of Scott's reduction?

As per this paper by Grädel, Kolaitis and Moshe Vardi, they discuss computational complexity of satisfiability problem in $\mathrm{FO^2}$, In order to do this they use Scott's reduction. Which is the ...
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approximate maximum clique given vertex cover

I have a non optimal vertex cover of size k of a graph G, and I want to get a (1+epsilon)-approximation kernel of size linear in k for maximum clique of G. One thing I got is that every clique in G ...
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a direct polynomial reduction from 3EQU-SUM to EQU-SUM problem [closed]

Given a multiset of integers $S$, in the Equ-Sum problem we want to check whether or not $S$ can be divided into two disjoint subsets, say $X_1$, $X_2$ such that $\sum_{x_i \in X_1}x_i = \sum_{x_j \...
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126 views

Reducing 3-XOR-SAT to HORN-SAT

In this question - XOR-SAT to Horn-SAT reduction, two algorithms are described for reducing any XOR-SAT formula to a HORN-SAT formula. My question is: say I limit the clauses of an XOR-SAT formula to ...
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What Is the Complexity of This Two-to-One Matching Problem?

Given a graph $G=(V,E)$ and a function $c:V\mapsto\{1,2\}$. The function $c(\cdot)$ divides the vertices into two disjoint sets $V_1$ and $V_2$, where for all $v_1\in V_1$, we have $c(v_1)=1$ and for ...
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380 views

What languages can be reduced to a NP-complete problem in polynomial time

NP-complete: Language is NP-complete, when it is in NP and every problem in NP is reducible to it in polynomial time. But what languages are reducible to a NP-complete problem (for example SAT) in ...
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Computing the edge orbits of a graph (and discussing definitions)

A (vertex) automorphism in a graph $G=(V,E)$ is a permutation $\sigma$ of the vertices that preserves adjacency, namely $\sigma(u) \sigma(v) \in E$ if and only if $uv \in E$. The automorphisms of a ...
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LogSpace reductions vs. PTime reductons for defining PSpace-completeness

Continuing https://cs.stackexchange.com/questions/90527/is-every-pspace-complete-problem-complete-with-respect-to-logspace-reductions : earlier, PSPACE-completeness was defined via logspace reductions ...
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Reductions in Descriptive Complexity

Reducing one problem to another are well known in various settings, such as many-one, randomized, truth-table, logspace or a whole slew of other reductions. Descriptive complexity can alternately ...
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Given $n\times n$ matrix $A$ with integer entries, find #$k$SAT formula that yields $\mathrm{perm}(A)>0$

For each #$k$SAT instance one can build a matrix $A$ such that $\mathrm{perm}(A) = F(\Sigma)$, where $\Sigma$ is the solution count of the $k$SAT formula and $F$ an easy to invert function. My ...
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Is there a notion of “inevitable reduction?”

I was just working on a semantics paper and realized I needed a notion of inevitable reduction. I came up with this definition: Let $\rightarrow$ be a binary relation. We say that $a$ inevitably ...
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Can we define a meaningful concept of exptime reductions (as opposed to polytime reductions) for classes like NEXP or NEEXP?

Typically we are only interested in polytime reductions as we are usually interested in showing a reduction from one NP-problem to another. However, if we consider larger complexity classes such as ...
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A partition problem in which some numbers may be cut

In the standard partition problem, we are given some numbers whose sum is $2s$ and have to decide whether they can be partitioned into two subset whose sum is $s$. It is known to be NP-hard. However,...
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Is Circuit Minimization $P$-hard under logspace reductions?

By Circuit Minimization, I am referring to the following decision problem. Circuit Minimization Input: A bit string $x$ and a number $k$. Question: Does there exist a Boolean Circuit $C$...
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Is there a P-complete language X such that succinct-X is in P?

I came across a paper called "A Note on Succinct Representation of Graphs". It seems that in the discussion section they claim that for any problem $X$ that is $\mathrm{P}$-hard under projections, $\...
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Why is the “general notion of a reduction […] inherent to the notion of self-reducibility”?

While reading "Computational Complexity: A Conceptual Perspective" by Oded Goldreich, I have come across the following passage, which I simply cannot get my head around: Note that the general ...
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Reduction of irregular graphs, to regular graphs, while preserving hamiltonicity

I am wondering if this is a topic that has had research done... If I could reduce irregular graphs to regular graphs (including replacing redundant node clusters with dummy nodes), while ensuring ...
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Reduction between functions that preserves time and space-complexity

Under which reduction(s) is the class $\mathsf{FTISP}(t(n), s(n))$ closed? Let $\mathsf{FTISP}(t(n), s(n))$ the class of functions from $\{0,1\}^*$ to itself that are computable by a Turing machine ...
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Isn't it “trivial” to represent/reduce any classical physics problem into a Spin-Glass which is NP-Complete?

In the late 80's there were several highly cited efforts to use Spin-Glass models to formulate other computational problems such as: Protein Folding and Neural Networks. Isn't it straight forward to ...
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Reduce $m$-clause 3SAT to PLANAR-3SAT in $O(m^{2-\varepsilon})$

The classic reduction from 3SAT to PLANAR-3SAT requires a removal of $O(m^2)$ crossings from a rectilinear representation of 3SAT with $m$ clauses. However, the crossing number inequality suggests ...
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On sparse complete sets and P vs L

Mahaney's Theorem tells us that if there is a sparse $NP$-complete set under polynomial-time many-one reductions, then $P = NP$. (See "Sparse complete sets for NP: Solution of a conjecture of Berman ...
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181 views

Verifying that a reduction is correct

Alice has a function $f: \{0,1\}^* \to \{0,1\}^*$ which can be computed in polynomial time. She claims that $x \in \mathrm{SAT} \iff f(x) \in \mathrm{CLIQUE}$. Alice sends the circuit computing $f$ on ...
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Random self reducibility and NP

I was reading the Wikipedia page Random self-reducibility and it states: If an NP-complete problem is non-adaptively random self-reducible the polynomial hierarchy collapses to $\Sigma_3$. I am ...
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On reduction between two classes?

https://link.springer.com/article/10.1007/s00153-013-0351-x gives seven reductions $m,c,d,p,btt(1),\ell,tt$. What does norm $1$ mean in $btt(1)$? Is there illustrative examples that help understand ...
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What is conjunctive truth table reduction?

What are conjunctive/disjunctive truth table reductions and how do they compare with other reductions?
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Certainty of mutual confirmation over faulty channels?

This is a very theoretical question, although I am sure the problem pops up in lots of IT and automation applications. Still, I prefer to formulate it in an action-movie scenario (a bit of the ...
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Proving properties about a compilation from one problem into another

Say I have two problems A and B. A is the shortest path problem with positive weights B is the shortest path problem (with potentially negative weights) I would like to show: There is no mapping m,...
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Calculus of Constructions: compress expression to its smallest form

I'm aware that the Calculus of Constructions is strongly normalizing, meaning every expression has a normal for that cannot be beta,eta-reduced further. So in fact this is the most efficient ...
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Prove that finding set of $k$ vertices $S$, such that $G{\setminus}S$ is claw-free is NP-Complete

The claw in a graph $G(V,E)$ consists of a vertex $v\in V$, and it's three neighbours - $\{x_1,x_2,x_3\}\in V\setminus \{v\}$, if $\{x_1,x_2,x_3\}$ form an independent set in $G$. The problem asks us ...
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193 views

Reduction from k-Almost Independent Set to Independent Set

The problem of $k$-Almost Independent Set is to decide whether or not $(G,m)$ where $G$ is a graph and $m \in \mathbb{N}$ has a subset of $m$ vertices that induces a subgraph with at most $k$ edges. I ...
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About reduction relation between $HP$ and $\mathcal{E}\mbox{*}$ [closed]

I'm studying Theory Of Computation and have some questions in the beginning: About reduction relation between $HP$ and $\mathcal{E}\mbox{*}$ $HP =$ {$<M,w>$ $|$ $M$ is a $TM$ and it halts on ...
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114 views

hardness of constant approximation of largest matching set

We say that $H$ is a matching graph if it contains $2n$ vertices and only $n$ vertex-disjoint edges, i.e. $H$ only contains those $n$ edges and no more. Given a graph $G=(V,E)$ a subset $U\subseteq V$...
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A conceptual question regarding hardness proofs by reduction [closed]

If we restrict the input domain of a known NP-hard problem P so that this restricted domain is equal to the input domain of another problem S, then show that we can reduce a solution to P given input ...
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Is intersection of $k \ge 3$ graphic matroids in P?

It is known that intersection of three general matroids is NP-hard (source), which is done via reduction from Hamiltonian cycle. The reduction uses one graphic matroid and two connectivity matroids. ...
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A list of XP-hard problems

The class $XP$ is the class of problems parameterized by $k$ that can be solved in time $n^{f(k)}$ for some function $f$ (each $k$ may require a different algorithm). In their book on parameterized ...
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Many-one reducibility equivalent for more general computational problems?

Many-one reducibility, denoted by $\leq_m$, is a binary relation between 2 decision problems which is defined as follows: $L' \leq_m L$ iff there exists a computable function $f$ (called a reduction) ...
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What are the best known reductions from SAT to CNF-SAT?

Problems Let SAT denote the following problem: Given a boolean formula, does there exist a satisfying assignment? Let CNF-SAT denote the following problem: Given a ...
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Reductions between languages of different densities?

The density of a language $X$ is a function $d_X \colon \mathbb{N} \to \mathbb{N}$ defined as $$d_X(n) = |\{x\in X \mid |x| \le n\}|.$$ Suppose $A$ and $B$ are languages over some finite alphabet, $A$ ...
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Is iszero of the untyped lambda calculus sound and complete? [closed]

I am using the following definitions in the notation of Haskell. In case it matters, I would like to use only the $\alpha,\beta,\eta$ reductions rather than the Haskell evaluation rules. ...
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270 views

UnambiguousSAT reductions

Let $\Pi$ be an $\mathsf{NP}$-complete problem. It is standard that $3SAT$ and $\Pi$ are reducible from each other. Let UnambiguousSAT, or USAT for short, denote the promise problem which is 3SAT but ...
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Is graph automorphism Karp-reducible to graph isomorphism under hidden subgroup representation?

The classical representations of the graph automorphism problem is Karp-reducible to the classical representation of the graph isomorphism problem. The sketch of proof for this can be written as ...
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154 views

Reduction Unbounded Knapsack < k-Exact Unbounded Knapsack

I'd like to have an explicit reduction among these two problems: (1) Unbounded Knapsack: Given a set of $n$ item types with weight $w_i$ and quality $q_i$ solve: $$maximize \sum_{i=1}^n q_ix_i $$ ...
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Does Karp reducibility yield a total order?

Or with other words, do we have that for every language $A$ and $B$, $A \leq_p B$ or $B \leq_p A$?
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Does PPAD really capture the notion of finding another unbalanced vertex?

Complexity class PPAD was invented by Christos Papadimitriou in his seminal 1994 paper. The class is designed to capture the complexity of search problems where the existence of a solution is ...
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446 views

Validity of exponentiation in a polynomial time reduction

I asked this question 10 days ago on cs.stackexchange here but I didn'y have any answer. In a very famous paper (in the networking community), Wang & Crowcroft present some $\mathsf{NP}$-...
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142 views

Graph Isomorphism Algorithm of Vertex Transistive Graphs and other

What are the best known Graph-Isomorphism algorithms for below graph classes- 1.vertex-transitive, 2. edge-transitive, 3.arc-transitive (or symmetric) 4.distance-transitive. Are they GI Complete? ...
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189 views

Complexity of permanent modulo prime

Given $M\in\Bbb Z^{n\times n}$ with $O(n)$ bit entries (could be all in $\{0,1\}$), $p$ a prime of $O(n^\alpha)$ bits for some $\alpha\in(0,1]$ and a $c,d\in\Bbb Z$ with $0\leq c<d<p$, is 'Is $\...