Questions tagged [approximation-algorithms]

Questions about approximation algorithms.

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171 views

Approximating the Radius of a (Dense) Graph

For a (dense) graph, computing its radius is as hard as computer "All Pairs Shortest Paths" (APSP) [1]. So we can focus on approximating the radius. A $(1+\epsilon)$-approximating of APSP for a ...
14
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2answers
581 views

Proof assistant usage in complexity theory research?

Considering the topics covered at a conference like STOC, are any algorithm or complexity researchers actively using COQ or Isabelle? If so, how are they using it in their research? I assume most ...
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68 views

Sparse-cut approximation for well connected graphs

Theorem: For any graph $G=(V,E)$, there is a polynomial time algorithm that finds a cut $S \subseteq V$ with conductance at most $\sqrt{2\big(1 − \lambda(G)\big)}$. If I understand UGC correctly, ...
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58 views

Studying the hardness of polynomial-time approximability using the concept of stability of approximation

In the Conclusion section, the author of this paper "Stability of Approximation Algorithms for Hard Optimization Problems" by Juraj Hromkovič, 1999 claims that Using the notion of stability one can ...
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104 views

Alternative Set Cover Algorithm With Doubling

I remember that I saw once an alternative to the greedy set cover algorithm that works as follows: Assign weight 1 to every element in the universe. Repeat steps 2 and 3 until the universe is covered:...
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112 views

Deterministic approximation algorithms for treewidth

As far as I understand, the factor $O(\sqrt{\log OPT})$ approximation algorithm for treewidth of Feige, Hajiaghayi, and Lee is randomized, and no deterministic approximation algorithm with this factor ...
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33 views

Sparse coding and matching pursuit algorithms

Is it true that all known sparse coding algorithms which work efficiently in practice don't have convergence proofs and always use an intermediate step of a matching/subspace pursuit algorithm on the ...
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0answers
84 views

Is it sufficient to only check on the vertices? Greedy algorithm

Suppose that I have a downwards closed Polyhedron and a vector $\omega$ and a greedy algorithm that goes as follows: Given an initial $x_0$, order the indices of $\omega$. Then for each $i$, solve $\...
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61 views

What is known about data structures for encoding a set while considering approximate Rank queries?

Consider a universe $\mathcal U\triangleq \{1,2,\ldots n\}$, and assume that we are given a set $S\subseteq \mathcal U$. There are many data structures that allow storing $S$ while answering Rank ...
3
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1answer
245 views

Looking for approximation class between NPO and Exp-APX

I'm trying to identify the approximation hardness of some maximization problem A. In problem A, finding a solution whose quality is 0 (i.e. such that the value returned by the objetive function is 0) ...
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221 views

Why is HyperLogLog (near-)optimal?

The original HyperLogLog paper claims that this probabilistic counting algorithm is "near-optimal". The relevant section of the paper reads: Clearly, maintaining $\epsilon$-approximate counts till ...
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2answers
2k views

Is the current best approximation ratio for Vertex Cover problem also a lower bound?

In textbook "Introduction to Algorithms" by Cormen, Leiserson, Rivest and Stein. in pp.1110-1111, they argue that the vertex-cover problem is a 2-approximation algorithm and it is lower bound so we ...
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202 views

On permanent of $\{\pm1,0\}$ matrices

Consider the problem of computing the permanent $Per(M)$ of a matrix $M\in\{0,-1,1\}^{n\times n}$ such that the result is bounded in absolute value, $|Per(M)|<B$ where $B$ is part of input. Is ...
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1answer
225 views

Compression algorithms for low-complexity strings?

Let $s$ denote a string over a finite alphabet, $n_s = |s|$ be the length of $s$, and $n_s^{*}$ denote the minimum description size of $s$ under a given computational model (TM, CFG, etc.). Are there ...
3
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3answers
171 views

Approaches for Theoretical Analysis of Estimates of Probability Distributions

Consider that you have a probability distribution p of some quantity X and you have obtained (via some algorithm) an estimate q of p according to some definition of closeness. Are there methods/papers ...
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186 views

Maximize the weight of MST + sum of vertex weights

I am considering a problem where the goal is to choose a subset of size $k$ of the vertices in a graph, such that the weight of their minimum spanning tree + the sum of their vertex weights is ...
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126 views

Given a matrix $A$ maximize the number of positive elements in $Ax$ under specific constraints for $x$

Let $A = [a_{ij}]$ be a symmetric matrix with nonnegative values and $k << n/2$ a given constant. We want to rearrange the columns of the matrix such that the number of rows with the following ...
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176 views

Positive cut algorithm on bipartite graphs with negative weights

Let $G=(V,E,w)$ be a bipartite graph with weight function $w:E→\{-1,1\}$. Is there an efficient (polynomial) algorithm for finding some positive (not necessarily maximum) cut of $G$, if one exists? If ...
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116 views

Truthful posted-price mechanism with optimal efficiency (social welfare)

I am interested in mechanism design. In the paper On Profit-Maximizing Envy-free Pricing, SODA, 2005, the authors provided a truthful competitive posted-price mechanism with $4\log h$ guarantee of ...
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142 views

Maximize number of edges covered by an independent set of vertices

Smallest vertex cover which is also an independent set asks about finding an independent set that covers all edges. This problem is known as the independent vertex cover problem and is equivalent to ...
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0answers
159 views

Algorithms to approximate a Riemann integrable function by a piecewise constant function

We know that any general function that is Riemann integrable can be approximated to arbitrary precision by piecewise constant functions. So in this regard, I was looking for references on algorithms (...
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2answers
257 views

Finding smallest context free grammar that generates a set of sets

Are there any results known about the size of smallest context free grammar that generates a set of sets? That is, I am given an alphabet $\Sigma$ as well as a set $S \subseteq \mathbb{P}(\Sigma)$ ...
3
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301 views

Approximating the VM packing problem

In the wikipedia article on bin-packing it is stated that A variant of bin packing that occurs in practice is when items can share space when packed into a bin. Specifically, a set of items could ...
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1answer
90 views

Density of multiples

I have an infinite collection of positive integers $n_1,n_2,n_3,\ldots$ and I would like to find the density of the numbers divisible by one or more of these.* If the density does not exist, the ...
6
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1answer
149 views

Brute force search algorithm for semidefinite programming (representation of spectrahedron)

I was wondering if there exists a brute force search algorithm for semidefinite programming problems. Specifically, can we find finite number of points in the positive semidefinite cone such that for ...
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1answer
161 views

Given oracle for Max-3SAT compute clauses that cannot be satisfied

We know that Max-3SAT is NP-hard to compute exactly (and also hard to approximate to a particular constant multiplicative factor). However, suppose you are given an oracle for Max-3SAT that tells you ...
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1answer
222 views

Online/approximate weighted and capacitated bipartite matching

I wish to take a look at online/approximate weighted and capacitated bipartite matching problem. Consider $G=\{L\cup R, E\}$, $|L|=n_1$, $|R|=n_2$, $|E|=m$ and $E\subseteq L\times R$. For each $r_i\...
7
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1answer
567 views

Ordering of a DAG minimizing some definition of cost

Consider a DAG $(V,A)$ with a topological ordering $(v_1,v_2,\ldots,v_n)$. I define the cost of this ordering as the maximum over all $1\leq i\leq n$ of $|\{j\leq i \mid \exists k>i: (v_j,v_k)\in A\...
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2answers
189 views

Solution/Hardness of the following (integer) budgeted problem?

I have no idea how to solve the following INTEGER problem or prove its hardness. Thanks for any help/comment/open discussion! Assume there are $N$ startups. For each startup $i$, you can invest $x_i\...
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104 views

algorithms for a large submatrix / general factor / quasi-biclique problem?

Given a sparse 0/1 matrix $X$, too large to fit in memory, with $m$ rows and $n$ columns, I'm looking for an algorithm for finding a submatrix (when one exists) with maximum number of rows such that ...
3
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1answer
260 views

How can we bound the optimal solution of the dual bin packing when we solve the knapsack problem for each bin?

I have these two problems: Problem 1 (Dual bin packing problem) Instance: A set of $n$ items where each item $i$ has weight $w_i$. A set of $k$ bins where each bin has capacity $W$. Question: Find ...
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101 views

Percolation probabilities

I have a finite undirected graph with a probability $p_e$ given for each edge $e$. This gives a random graph by removing each edge e with probability $1-p_e$ independently of the others. I'm ...
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125 views

Weighted $l_1$ distance

So there are many well known algorithms for approximate nearest neighbor on the $\ell_1$ distance. My question is, what about the weighted version of the problem (where the weights are specified along ...
2
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1answer
778 views

Max-sum graph-partition for maximizing intra-edge weights?

I would like to know if the following problem has already been studied, and if so how is it called. In particular I'm interested in approximability results. Input: A graph G with negative or non-...
2
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1answer
808 views

Partial cover approximation

We have a set of elements $E=\{e_1, e_2, \ldots, e_m\}$, and $n$ subsets of $E$: $S_1, S_2, \ldots, S_n$ The union of those subsets is $E$, and each subset $S_i$ has a non-negative weight $w_i$. The ...
5
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180 views

Fast Approximation Algorithms for Covering Design

The covering design problem is as follows: We are given a universe $\mathcal{U}$ of size $n$. By $C(n,k,l)$ we denote the smallest cardinality of any set system $\mathcal{A} \subset 2^\mathcal{U}$ ...
2
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0answers
93 views

About representability of optimization versions of NP-complete questions as polynomial optimization over the hypercube

Naively, in my very limited awareness, it feels that the Max-CUT is a very "special" NP-Hard problem because for a graph with edge-set $E$, it can be written as the question of trying to maximize a $n$...
5
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1answer
148 views

Does k-PATH admit a constant approximation?

In the $k$-PATH problem, we receive as input a graph $G$ and an integer $k$. The goal is to decide whether there exists a simple path of length $k$ in $G$. A $\alpha$-approximation for $k$-PATH is an ...
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0answers
45 views

Stochastic optimization with erroneous oracles

I am interested in a class of optimization problems of which we know that the input variable is first subjected to noise $\xi$ before entering the data-producing process $f$. I write the objective in ...
4
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1answer
1k views

Maximizing a monotone supermodular function s.t. cardinality

I've tried to comb the literature and seen a lot of references to results that almost but don't quite seem to address this. Question: Is it known to be true or is there a hardness result ...
3
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2answers
486 views

Quantum complexity of maximum inner product search

Given two matrices $X \in \mathbb{R}^{m \times k}$, $Y \in \mathbb{R}^{n \times k}$, maximum inner product search (MIPS) asks for the largest $l$ entries of $X Y^T$. Typically $k \ll m, n$ (many ...
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0answers
243 views

Maximizing the number of selected edges with opposing requirements

Consider the following problem: Input: a complete bipartite graph $G$ with its edges colored either white or black, a number $k$. Output: a subset of vertices $W$ of size $k$ which maximizes the ...
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116 views

L-reduction From Matrix-Tiling To Minimal Dominating Set in Unit Disk Graph

Recently I read this paper which was published in FOCS2007. In section 4, just before Theorem 4.2, the author mentioned that the gadget construction of Minimum Dominating Set in UDG is similar to ...
3
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1answer
333 views

What is the reverse of greedy algorithm for setcover?

A common approach to approximating SETCOVER is the greedy algorithm (Algorithm 2.2 Vazirani). This algorithm greedily picks the most cost-effective subset at each iteration, removes covered elements, ...
5
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1answer
701 views

Is there an approximation algorithm for MAX k DOUBLE SET COVER?

Given a set system $(X,\mathcal S)$, let us say that a subset $\mathcal C\subseteq \mathcal S$ doubly covers a vertex $x$ in $X$ if $x$ is contained in at least two sets of $\mathcal C$. Let us define ...
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362 views

Complexity of approximating the range of a matrix

Given an $m$ by $n$ matrix $M$ with $m \leq n$ and elements from $\{-1,1\}$, let us define: $$S_M = |\{Mx : x \in \{-1,1\}^n\}|.$$ I believe that it is NP-hard to compute $S_M$ exactly, by applying ...
3
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0answers
126 views

Complexity of minimizing monotone arithmetical formulas

Let's say that I have a multi-variate arithmetical expression $A(x_1, \ldots, x_n)$ that uses addition and multiplication operations and is also in a very simple form of sums of products, e.g., $A_1(...
3
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1answer
232 views

Which is the approximation class of Minimum 0-1 integer programming if only non-negative integers are allowed?

I'm wondering which is the approximation class of Minimum 0-1 Integer Programming if only non-negative integers are used. That is: minimize $c^T \cdot x$, with $x\in \{0,1\}^n$ and $c\in (\mathbb{Z}^...
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0answers
74 views

Distributing bags of apples equally

Assume you have $N$ bags of apples that you want to equally distribute to $K$ people. Each bag contains $n_i$ apples and you are not allowed to open and divide the bags; you must distribute the bags ...
3
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1answer
301 views

Approximation algorithms for the maximum $2$-independence set problem

I am interested in approximating the maximum $2$-independent set problem in arbitrary graphs. In a graph $G$ a set $I$ of vertices is called $2$-independent if the distance between any two distinct ...

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