Questions tagged [approximation-algorithms]

Questions about approximation algorithms.

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12
votes
3answers
695 views

A Multi-cut Problem

I'm looking for a name or any references to this problem. Given a weighted graph $G = (V, E, w)$ find a partition of the vertices into up to $n = |V|$ sets $S_1,\ldots,S_n$ so as to maximize the ...
17
votes
3answers
485 views

Is there a constant factor approximation algorithm for 2D rectangle coloring problem?

The problem we consider here is the extension of the well-known interval coloring problem. Instead of intervals we consider rectangles having sides parallel to axes. The objective is to color the ...
12
votes
3answers
561 views

What are the problems with the best approximation ratio achieved by algorithm returning uniformly random solution?

What are the problems with the best known approximation ratio achieved by an algorithm returning a uniformly random solution? I know one such example for permutation flow shop problem $F|perm|C_{max}...
7
votes
2answers
776 views

Approximation algorithms for MAX-CUT, when sizes of partition sets are fixed

The MAX-CUT problem has constant factor approximation, but we can't control the sizes of the sets in resulting partition. What is known about maximizing cut size, if we restrict one part of the ...
17
votes
2answers
761 views

Set Cover for Permutation Matrices

Given a set S of nxn permutation matrices (which is only a small fraction of the n! possible permutation matrices), how can we find minimal-size subsets T of S such that adding the matrices of T has ...
10
votes
1answer
225 views

Relaxing $\ell_0$ constraints in an optimization

I have a feasibility question that can be framed as follows. I'm given a point $p$ in a $d$-dimensional vector space, and I want to find the closest point $q$ to $p$ that satisfies a set of "$\ell_0$ ...
15
votes
1answer
446 views

Graph decompositions for combining “local” functions of vertex labelings

Suppose we want to find $$\sum_x \prod_{ij \in E} f(x_i,x_j)$$ or $$\max_x \prod_{ij \in E} f(x_i,x_j)$$ Where max or sum is taken over all labelings of $V$, product is taken over all edges $E$ for a ...
13
votes
3answers
4k views

Is there an online-algorithm to keep track of components in a changing undirected graph?

Problem I have an undirected graph (with multi-edges), which will change over time, nodes and edges may be inserted and deleted. On each modification of the graph, I have to update the connected ...
19
votes
1answer
344 views

What are the best possible time/error tradeoffs for approximate solution of linear programs?

For concreteness consider the LP for solving a two-player zero-sum game where each player has $n$ actions. Suppose each entry of the payoff matrix $A$ is at most 1 in absolute value. For simplicity ...
35
votes
3answers
4k views

Max-cut with negative weight edges

Let $G = (V, E, w)$ be a graph with weight function $w:E\rightarrow \mathbb{R}$. The max-cut problem is to find: $$\arg\max_{S \subset V} \sum_{(u,v) \in E : u \in S, v \not \in S}w(u,v)$$ If the ...
8
votes
2answers
711 views

Approximation Algorithms for MAXSAT

Trying to find the optimal solution to WEIGHTED-MAX-3SAT, the weighted version of the 3-SAT optimization problem, is NP-hard. In fact, even approximating the non-weighted version of MAX-SAT ...
4
votes
1answer
433 views

Better approximation for special case of 3-hitting set

I have a question based on 3-Hitting Set problem. In this problem, we are given a universal set U of size n and a set of subsets S such that $\forall $ s $\in$ S |s|<=3. FOr this problem, Integer ...
4
votes
0answers
224 views

Follow-up on Nair/Tetali's Correlation Decay Tree for hypergraphs?

I'm wondering if anybody has followed up on Nair/Tetali's correlation decay tree construction for hypergraphs. I didn't find anything relevant in back-citation on google scholar. Interesting question ...
26
votes
3answers
951 views

When is relaxed counting hard?

Suppose we relax the problem of counting proper colorings by counting weighted colorings as follows: every proper coloring gets weight 1 and every improper coloring gets weight $c^v$ where $c$ is some ...
8
votes
2answers
964 views

Integer Factoring via Lattice Reduction?

I found a paper titled "Factoring integers and computing discrete logarithms via diophantine approximation" by C. P. Schnorr from 1993. It looks like a probabilistic method with expected polynomial ...
22
votes
2answers
1k views

Polynomial time approximation algorithms for machine scheduling: how many open problems are left?

In 1999, Petra Schuurman and Gerhard J. Woeginger published the paper "Polynomial time approximation algorithms for machine scheduling: Ten open problems". Since then, to the best of my knowledge, ...
38
votes
9answers
3k views

Optimal greedy algorithms for NP-hard problems

Greed, for lack of a better word, is good. One of the first algorithmic paradigms taught in introductory algorithms course is the greedy approach. Greedy approach results in simple and intuitive ...
11
votes
2answers
508 views

Average distortion embeddings

Consider two metric spaces $(X, d)$ and $(Y, f)$, and an embedding $\mu : X \rightarrow Y$. Traditional metric space embeddings measure the quality of $\mu$ as the worst-case ratio of original to ...
14
votes
1answer
905 views

Integer relation detection for Subset Sum or NPP?

Is there a way to encode an instance of Subset Sum or the Number Partition Problem so that a (small) solution to an integer relation yields an answer? If not definitely, then in some probabilistic ...
11
votes
4answers
482 views

Dimensionality reduction with slack?

The Johnson-Lindenstrauss lemma says roughly that for any collection $S$ of $n$ points in $\mathbb{R}^d$, there exists a map $f:\mathbb{R}^d \rightarrow \mathbb{R}^k$ where $k = O(\log n/\epsilon^2)$ ...
5
votes
1answer
416 views

High probable polynomial time algorithm for NP-hard problems?

Many NP-complete or NP-hard problems are addressed under the assumption that the problem instances are uniformly distributed. However, it is not true for real world applications. One example is the ...
8
votes
2answers
350 views

complexity of fitting models to data

Suppose $f:\mathbf{R}\times \mathbf{R} \to \mathbf{R}$ is some some continuous function $x_1 \ldots x_n$ is a set of real values, and we'd like to compute $\text{argmin}_a \sum_i f(a,x_i)$ to ...
11
votes
2answers
4k views

Any fast algorithm for minimum cost feedback arc set problem?

In a directed graph, $G=(V,E)$, $F\subset E$, if $G\setminus F$ is a DAG(directed acyclic graph), $F$ is called a feedback arc set. If each edge is associated with a weight $w$, the minimum cost ...
45
votes
8answers
6k views

The importance of Integrality Gap

I always had trouble in understanding the importance of the Integrality Gap (IG) and bounds on it. IG is the ratio of (the quality of) an optimal integer answer to (the quality of) an optimal real ...
27
votes
4answers
2k views

Bounded-cardinality bounded-frequency set cover: hardness of approximation

Consider the minimum set cover problem with the following restrictions: each set contains at most $k$ elements and each element of the universe occurs in at most $f$ sets. Example: the case $k = 4$ ...

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