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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Are the Eigendecomposition and Singular Value Decompositions in the class P?

I can run, for instance, np.linalg.eig or np.linalg.svd on my computer in polynomial time. However, my understanding is that if the intermediate steps require too many bits to express and give NaNs or ...
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Reducing euclidean TSP of smaller size to euclidean TSP of bigger size [closed]

Assume I have a euclidean TSP solver that is optimal, but it can only solve inputs with exactly $N$ vertices. Let's call it the N-solver. Now, I have an input with $K$ vertices in the 2D plane, where $...
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-1 votes
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Showing that a modification of an NP-Complete problem is also NP-Complete

In this question I give a modified version of the knapsack problem, which I call the "extended knapsack problem". I want to show that this "extended" problem is NP-Complete, but I ...
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Parameterized complexity of Hitting Set with slightly bigger parameter

The Hitting Set problem, when parameterized by the size $k$ of the hitting set, is W[2]-hard. Is it also W[2]-hard when parameterized by $k$ plus the number of subsets in the instance? I explain in a ...
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Is Power Dominating Set in W[2]?

I'm interested in the Power Dominating Set problem: given a graph, find a power dominating set $D$ of size at most $k$. A power dominating set is a set of vertices such that it "observes" ...
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Reducing counting minimal vertex covers to counting minimum cardinality vertex covers

Consider two problems. Problem 1: Given a graph $G = (V, E)$, find the number of minimum cardinality vertex covers of $G$. Problem 2: Given a graph $G = (V, E)$, find the number of minimal vertex ...
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APX-hardness of Max-3-SAT(5)

Max-3-SAT($k$) for a natural number $k$ is the task of finding the maximum number of satisfiable clauses in a Boolean formula in CNF, where every clause contains at most 3 literals and every variable ...
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Invisible electric fence even if P = NP?

Scott Aaronson has suggested that one argument in favor of $\mathsf{P} \ne \mathsf{NP}$ is that there seems to be an invisible electric fence separating $\mathsf{NP}$-complete problems from problems ...
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Does such a graph exist? [closed]

[EDITED FOR CLARITY] Does there exist an edge-colored graph $G$ with the following properties? $G$ has a vertex $r$ with exactly three, distinctly colored, incident edges: $(r, u)$, $(r, v)$, $(r, w)$...
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Worst to average case reductions for quantum complexity classes

I am studying worst to average case reductions for different complexity classes. Consider quantum complexity classes like QMA, QSZK, or QIP. Is it known or believed that these classes are amenable to ...
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Complexity of reachability in directed rooted forests

I'm trying to figure out the complexity of the reachability problem having as input a directed rooted forest, i.e., given a set of directed rooted trees and two vertices $s$ and $t$, tell if $s$ and $...
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A reduction from the maximum $k$-closure problem to the clique problem

Fix a partially ordered set $(P, \le)$ with $N$ elements and real weights $w(p)$ for each $p \in P$. A subset $S \subset P$ is called closed if for any $x, y$ with $y \in S$ and $x \le y$ we also ...
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Can this NP-hardness proof for Super Mario Brothers (and other games) be simplified?

In "Classic Nintendo Games are (Computationally) Hard", a generalized framework based on reducibility of 3-SAT for proving NP-hardness of classic Nintendo games is presented, and several ...
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complexity class of a function - linear combinations and reductions (Fermionant, immanant, $GL_n$ representations)

The fermionant is a matrix function from physics, which is indexed by a positive integer $k$: \begin{align} \operatorname{Ferm}_k(A) = \sum_{\lambda} d_{\lambda}^{(k)} \operatorname{Imm}_{\lambda^T}(A)...
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3SAT to 1-in-3SAT reduction with additonal constraints

The simplest Reduction for 3-SAT to 1-in-3-SAT reduction is as follows: For each 3SAT clause: $x+y+z=1$ Introduce 4 new variables $\{a, b, c, d\}$ and replace original clause with below 3 clauses: $R(...
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Proving not NP-complete by non-existence of gadget

Suppose we suspect a problem to be polynomial time solvable, but we are unable to prove this. So, we attempt to prove that the problem cannot be NP-hard. Known proofs in this direction show that if ...
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The complexity of tensor formula evaluation problem over an infinite field

In the paper The complexity of tensor calculus by C. Damm, M. Holzer and P. McKenzie (link), the authors reduced the problem of computing the permanent of 0/1-matrices to that of evaluating tensor ...
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The graph of problem reductions

A classical approach to study the complexity of a problem $P$ is to efficiently reduce a well known problem $P'$ to $P$, thus showing that $P$ is at least as difficult as $P'$. The TCS literature ...
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Knowing if there are two solutions to the subset sum problem

I was wondering if there are any results that say how hard it is to answer the question are there TWO subsets that sum to a fixed value? In other words, the subset sum problem but asking if there are ...
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Is solving the following system of boolean equations NP-hard?

I reduced a problem I'm currently working on to the following system of boolean equations: $$ X_i \iff \begin{cases} \bigvee_{B \in A_i} \bigwedge_{k \in B} X_k \\ true \\ false \end{cases} $$ Where $|...
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Some examples of tools to demonstrate problem is in $NC$ [closed]

Unlike the class $P$ or $NP$ the class $NC$ does not have any complete problems. To show a problem is in $NC$ one needs to marshal efforts to directly show the problem is in $NC$ since there are no ...
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3-partition problem without the restriction to triplets

In the standard 3-partition problem, there are $3 m$ integers, their sum is $m T$, and they have to be partitioned into $m$ subsets of sum $T$ and size $3$. Consider the variant without the ...
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Is it possible to reduce an NP language to a NEXP language with exponentially smaller input length?

Suppose we have an NP-complete language $L_1$ and a NEXP-complete language $L_2$. For any deterministic exptime machine $M_1$ with oracle access $M_1^{L_1}$, is it possible to find a deterministic ...
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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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12 votes
1 answer
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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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2 votes
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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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1 vote
1 answer
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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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2 votes
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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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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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8 votes
2 answers
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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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4 votes
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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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5 votes
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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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8 votes
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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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8 votes
3 answers
861 views

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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3 votes
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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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14 votes
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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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7 votes
1 answer
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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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5 votes
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114 views

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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10 votes
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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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4 votes
1 answer
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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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4 votes
0 answers
191 views

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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2 votes
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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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