# Questions tagged [approximation-algorithms]

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### Is finding the best permutation an NP-Complete problem?

We have a matrix $M$ of size $n$ by $n$ where $M[i][j] \ge 0$ and $M[i][i] = 0$. We want to create a permutation of integers $[1,\dots,N]$, like $\langle P_1, P_2,\dots,P_n \rangle$, such that  \...
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### Is the Maximum Coverage Problem Remains as Hard when Taking Most Sets?

In the maximum coverage problem (also known as max k-cover) we are given a universe $U = \{e_1,\ldots, e_n\}$ of elements, a collection $F = \{S_1,\ldots, S_m\} \subseteq 2^U$ of sets over $U$, and an ...
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### Partial Hamiltonian Path Optimization Problem

Let $G = (V,E)$ be a directed graph. Define the optimization problem in which the goal is to find a subset of edges in $G$ of maximum cardinality, such that (i) the in-degree and out-degree of each ...
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### How well can shortest common supersequence over small alphabet size be approximated?

Given a list $L$ of sequences of the first $n+1$ natural numbers, how well can we approximate the shortest common supersequence of all sequences in $L$? The paper here shows that if $n$ is not ...
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### Shortest sequence that contains a given list of sequences as subsequences

Given an alphabet with $n$ characters, and a list $L$ of sequences can we approximately find the shortest sequence that contains all sequences of $L$ as subsequences? Very similar to the question ...
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### References for algorithms to compute approximating polytopes for arbitrary convex sets

There is a vast theoretical literature on approximating convex, compact bodies in $d$-dimensional space $\Bbb R^d$ by convex polytopes. One of the main results in this area is that under some mild ...
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### Working out the constants and probabilities of Stockmeyer's approximate counting algorithm

Stockmeyer's 1983 result on approximate counting using a randomness states that if we have some SAT instance $x$ with $C(x)$ satisfying assignments, then we can find the minimum set of $m$ hash ...
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### What infinite sums cannot be approximated in polynomial time?

The following is from the book Geometric algorithms and combinatorial optimization: It shows an infinite sum that has an FPTAS (= an $\epsilon$-approximation can be computed using poly($1/\epsilon$) ...
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### Hardness of Coloring based on a Black-Box Hardness of Independent Set

It is well known that both vertex coloring and maximum independent set are very hard to approximate in polynomial time under standard complexity assumptions. Given a black-box hardness of independent ...
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### maximum independent set in graphs with small number of edges

For the classic maximum independent set problem, a hardness of approximation result of $n^{1-\varepsilon}$ is known by [Hastad, 1996] assuming $\textsf{NP} \not \subseteq \textsf{ZPP}$, where $n$ is ...
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1 vote
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### A variant of the generalised assignment problem

I am trying to solve this problem: There are $N$ workers and $T$ tasks. Each task can be assigned to at most one worker. Each worker can be assigned any number of tasks. The profit obtained by ...
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### Approximation ratio of randomized rounding for integral multi-commodity flow

In [1], Raghavan and Thompson showed that we can use randomized rounding to approximate integral multi-commodity flow and routing with congestion. The result is that suppose the optimal solution is $W$...
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### FPTAS for switching deals

The local supermarket offers seasonal deals on their apples and oranges. You want either apples or oranges on any given day, but don't know until you wake up; you want to minimise your cost. You ...
1 vote
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### How to understand this evolutionary algorithm lower bound calculation?

I have a proof that I understand the most of it except one step Lemma 10. The expected number of steps the $(1+1)$ EA takes to optimize a linear function with all non-zero weights is $\Omega(n \ln n)$....
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### Stable/Robust Traveling Salesman Approximation Methods

I was wondering if there are TSP approximations that are "stable". More specifically, consider the set $G = x_1, ..., x_n$ and the set $G^* = G \cup x_{n+1}$, where $x_i$ are points in $R^d$....
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### FPRAS to estimate the probability to get a cyclic subgraph of a directed graph

Consider a directed graph $G = (V, E)$ whose edges are annotated with independent probabilities of existence. This gives a probability distribution on the subgraphs of $G$; for instance, if each edge ...
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### Techniques for solving huge linear programs

During the solution of some computational problem, we have arrived at a linear program of the following form: \begin{align*} \text{maximize} ~~ c x \\ \text{subject to} ~~ A x \leq b, x \geq 0 \...
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### Approximating the utilitarian welfare minus a constant

Assume we have $n$ agents and $m$ indivisible goods that need to be allocated among the agents such that their sum of utilities is maximized. Denote the set of allocations by $\mathcal{A}$ and the ...
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### Finding $k \times k$ rectangle in a matrix with maximum sum

Given an $n \times n$ matrix $A$ with $0-1$ entries, I want to maximize $\sum\limits_{i \in I, j \in J} a_{ij}$ subject to $|I| = |J| = k.$ I expect the problem to be NP-hard, so I want a polynomial ...
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### Find Combinations of fibonacci values to approximate a target value given $F(A,B,C,D) = (A + B + C) / D$

I am able to solve this using brute force but curious if there is a better approach. Given the function $F(A,B,C,D) = (A + B + C) / D$ where each variable is in the first 7 distinct values of the ...
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### Approximate Matrix Multiplication with approximation guarantees that ignore large elements?

Approximate matrix multiplication is a technique to replace a matrix product $A^t B$ with a smaller product $(\Pi A)^t(\Pi B)$. Intuitively, if $\Pi$ is chosen from a suitable distribution that has ...
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### Generalized assignment problem with overall budget

The problem has N tasks. We have M workers. We have the cost of assigning task i to worker j. We have a profit for assigning task i to worker j. We want to assign each task to exactly one worker. One ...
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### A simultaneous FPTAS for both max-min and min-max number partitioning

The multiway number partitioning problem has two optimization variants: in one variant the goal is to minimize the largest bin sum (the "makespan"), and in the other variant the goal is to ...
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### Bin Covering problem with variable bin sizes

I have a decision problem that I cannot seem to map to a standard studied problem, although it seems similar to a few. I am wondering if anyone has come across this problem before, or if someone can ...
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### When Exponential Costs are Essential for NP-Hardness?

In many NP-hard problem there is a budget constraint. Each element $e$ in the instance has a certain cost $c(e)$ and a profit $p(e)$; a feasible solution $S$ for the considered problem cannot exceed ...
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### Computing an approximate root of a two-dimensional monotone function

Let $f$ be a Lipschitz-continuous function from the square $[-1,1]^2$ to itself, satisfying the following conditions: For all $y\in [-1,1]$: $~~~~f(-1,y)_1\leq 0\leq f(1,y)_1$, and $f(x,y)_1$ is ...
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1 vote
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### 3 Matroid Intersection, a Special Case

It is well known that finding a maximum cardinality (or weight) common independent set in the intersection of 3 matroids is APX-Hard. Question: Does this problem remain NP-Hard if one of the matroids ...
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### Balls in monochromatic bins

Suppose we have a collection of $m$ balls in $k$ different colors. Let $b_i$ be the number of balls with color $i$, so $\sum_{i=1}^k b_i = m$. Assume we have $n$ bins with capacities $c_1, \dots, c_n$,...
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### Confusion with the definition of Online Set Cover

I am confused on a technicality on how Online Set Cover is defined. One way to define it is: We are given a collection of sets $\mathcal{S}$ upfront, and in each time-step an element arrives to be ...
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### $k-$median problem and filtering technique Lin and Vitter

I read a paper from Tardos et al. about $k-$medians in metric space problem: Given $N$ as set of points in metric space with distance function $c_{ij}$ for each $i,j\in N$, demand $d_i$ for each point ...
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### Why is the competitive ratio defined as $\mathbb{E}(ALG)/\mathbb{E}(OPT)$ vs $\mathbb{E}(ALG/OPT)$?

It seems like the consensus is to define an $\alpha$-competitive algorithm if $\mathbb{E}_R(ALG) \geq \alpha \mathbb{E}_R(OPT)$ where $\mathbb{E}_R$ is the expected value taken across the problem ...
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1 vote
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### Approximation algorithm for non-bipartite Euclidean matching

What is the current best (in terms of running time) (1+\epsilon)-approximation algorithm (both randomized and deterministic) for non-bipartite Euclidean (in higher dimension) matching? There are ...
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### Can one obtain an FPTAS for Knapsack by Rounding Weights (and not Profits)?

In the knapsack (KP) problem we are given a set $I = \{1,\ldots,n\}$ of items, each item $i \in [n]$ has a weight $w_i$ and a profit $p_i$. A classic Fully Polynomial time approximation scheme (FPTAS) ...
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### Examples of Gaussian randomized algorithms

I've been thinking about algorithms of the form where a quantity $c$ can be viewed as the expectation of some estimator (random variable) $X$ and the expectation is taken over some multivariate ...
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### Approximation algorithm for balanced bipartite independent set?

The Problem: Given a bipartite graph $G = (L,R,E)$ with $|L|=|R|=n$, the balanced bipartite independent set problem asks us to output the largest vertex subsets $A\subseteq L, B\subseteq R$ of equal ...
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The work by Jerrum & Sinclair (1989) describes an approximative approach to determining the number of matchings $|M_\ast(G)|$ in a graph $G=(V,E)$. The fundamental ingredient of the approximation ...