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23
Improved approximation algorithms for uncapacitated facility location (Extended Abstract)
, 1998
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A reputation system to increase MIXnet reliability
 Information Hiding (IH 2001
, 2001
"... Abstract. We describe a design for a reputation system that increases the reliability and thus efficiency of remailer services. Our reputation system uses a MIXnet in which MIXes give receipts for intermediate messages. Together with a set of witnesses, these receipts allow senders to verify the co ..."
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Cited by 62 (12 self)
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Abstract. We describe a design for a reputation system that increases the reliability and thus efficiency of remailer services. Our reputation system uses a MIXnet in which MIXes give receipts for intermediate messages. Together with a set of witnesses, these receipts allow senders to verify the correctness of each MIX and prove misbehavior to the witnesses. We suggest a simple model and metric for evaluating the reliability of a MIXnet, and show that our reputation system improves over randomly picking MIX paths while maintaining anonymity. 1
Modelbased overlapping clustering
 In KDD
, 2005
"... While the vast majority of clustering algorithms are partitional, many real world datasets have inherently overlapping clusters. Several approaches to finding overlapping clusters have come from work on analysis of biological datasets. In this paper, we interpret an overlapping clustering model prop ..."
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Cited by 41 (7 self)
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While the vast majority of clustering algorithms are partitional, many real world datasets have inherently overlapping clusters. Several approaches to finding overlapping clusters have come from work on analysis of biological datasets. In this paper, we interpret an overlapping clustering model proposed by Segal et al. [23] as a generalization of Gaussian mixture models, and we extend it to an overlapping clustering model based on mixtures of any regular exponential family distribution and the corresponding Bregman divergence. We provide the necessary algorithm modifications for this extension, and present results on synthetic data as well as subsets of 20Newsgroups and EachMovie datasets.
Faulttolerant facility location
 in Proceedings of the 14th Annual ACMSIAM Symposium on Discrete Algorithms
, 2003
"... We study a faulttolerant generalization of the classical uncapacitated facility location problem. We want to open a subset of facilities from a given set F and assign each client j in a given set D to rj ≥ 1 distinct open facilities so as to minimize the sum of the facility opening costs and the cl ..."
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Cited by 30 (4 self)
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We study a faulttolerant generalization of the classical uncapacitated facility location problem. We want to open a subset of facilities from a given set F and assign each client j in a given set D to rj ≥ 1 distinct open facilities so as to minimize the sum of the facility opening costs and the client assignment costs. We also consider the faulttolerant kmedian problem where instead of facility costs we are given a number k of facilities that may be opened, and the objective is to minimize only the assignment cost. Multiple facilities provide a safeguard against failures. If the facility closest to a client ‘fails’, the other facilities assigned to it could be used to serve it, e.g., in designing a network involving the placement of caches or routers, one would like to connect a client to multiple caches or routers so as to be resistant under node or link failures. We consider the case where the distances, cij, formametric.
Provably Good Global Buffering Using an Available Buffer Block Plan
 PLAN,” PROCEEDINGS OF THE IEEE/ACM INTERNATIONAL CONFERENCE ON COMPUTERAIDED DESIGN
, 2000
"... To implement highperformance global interconnect without impacting the performance of existing blocks, the use of buffer blocks is increasingly popular in structuredcustom and blockbased ASIC/SOC methodologies. Recent works by Cong et al. [6] and Tang and Wong [25] give algorithms to solve the bu ..."
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Cited by 26 (5 self)
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To implement highperformance global interconnect without impacting the performance of existing blocks, the use of buffer blocks is increasingly popular in structuredcustom and blockbased ASIC/SOC methodologies. Recent works by Cong et al. [6] and Tang and Wong [25] give algorithms to solve the buffer block planning problem. In this paper we address the problem of how to perform buffering of global nets given an existing buffer block plan. Assuming as in [6, 25] that global nets have been already decomposed into twopin connections, we give a provably good algorithm based on a recent approach of Garg and Könemann [8] and Fleischer [7]. Our method routes connections using available buffer blocks, such that required upper and lower bounds on buffer intervals – as well as wirelength upper bounds per connection – are satisfied. Unlike [6, 25], our model allows more than one buffer to be inserted into any given connection. In addition, our algorithm observes buffer parity constraints, i.e., it will choose to use an inverter or a buffer ( = colocated pair of inverters) according to source and destination signal parity. The algorithm outperforms previous approaches [6] and has been validated on toplevel layouts extracted from a recent highend microprocessor design.
Scheduling Data Transfers in a Network and the Set Scheduling Problem
 In Proceedings of the 31st Annual ACM Symposium on Theory of Computing
, 1999
"... In this paper we consider the online ftp problem. The goal is to service a sequence of file transfer requests given bandwidth constraints of the underlying communication network. The main result of the paper is a technique that leads to algorithms that optimize several natural metrics, such as maxs ..."
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Cited by 19 (2 self)
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In this paper we consider the online ftp problem. The goal is to service a sequence of file transfer requests given bandwidth constraints of the underlying communication network. The main result of the paper is a technique that leads to algorithms that optimize several natural metrics, such as maxstretch, total flow time, max flow time, and total completion time. In particular, we show how to achieve optimum total flow time and optimum maxstretch if we increase the capacity of the underlying network by a logarithmic factor. We show that the resource augmentation is necessary by proving polynomial lower bounds on the maxstretch and total flow time for the case where online and offline algorithms are using samecapacity edges. Moreover, we also give polylogarithmic lower bounds on the resource augmentation factor necessary in order to keep the total flow time and maxstretch within a constant factor of optimum.
Approximation Algorithms for Clustering Problems
, 2004
"... Clustering is a ubiquitous problem that arises in many applications in different fields such as data mining, image processing, machine learning, and bioinformatics. Clustering problems have been extensively studied as optimization problems with various objective functions in the Operations Research ..."
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Cited by 14 (5 self)
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Clustering is a ubiquitous problem that arises in many applications in different fields such as data mining, image processing, machine learning, and bioinformatics. Clustering problems have been extensively studied as optimization problems with various objective functions in the Operations Research and Computer Science literature. We focus on a class of objective functions more commonly referred to as facility location problems. These problems arise in a wide range of applications such as, plant or warehouse location problems, cache placement problems, and network design problems where the costs obey economies of scale. In the simplest of these problems, the uncapacitated facility location (UFL) problem, we want to open facilities at some subset of a given set of locations and assign each client in a given set D to an open facility so as to minimize the sum of the facility opening costs and client assignment costs. This is a very wellstudied problem; however it fails to address many of the requirements of real applications. In this thesis we consider various problems that build upon UFL and capture additional issues that arise in applications such as, uncertainties in the data, clients with different service needs, and facilities with interconnectivity requirements. By focusing initially on facility location problems in these new models, we develop new algorithmic techniques that will find application in a wide range of settings. We consider a widely used paradigm in stochastic programming to model settings where the underlying data, for example, the locations or demands of the clients, may be uncertain: the 2stage with recourse model that involves making some initial decisions, observing additional information, and then augmenting the initial decisions, if necessary, by taking recourse actions. We present a randomized polynomial time
On the Crossing Spanning Tree Problem
 Proceedings of 7th International Workshop on Approximation Algorithms for Combinatorial Optimization Problems, APPROX 2004
"... Abstract. Given an undirected nnode graph and a set C of m cuts, the minimum crossing tree is a spanning tree which minimizes the maximum crossing of any cut in C, where the crossing of a cut is the number of edges in the intersection of this cut and the tree. This problem finds applications in fie ..."
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Cited by 14 (3 self)
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Abstract. Given an undirected nnode graph and a set C of m cuts, the minimum crossing tree is a spanning tree which minimizes the maximum crossing of any cut in C, where the crossing of a cut is the number of edges in the intersection of this cut and the tree. This problem finds applications in fields as diverse as Computational Biology and IP Routing Table Minimization. We show that a greedy algorithm gives an O(r log n) approximation for the problem where any edge occurs in at most r cuts. We then demonstrate that the problem remains NPhard even when G is complete. For the latter case, we design a randomized algorithm that gives a tree T with crossing O((log m +logn) · (OPT +logn)) w.h.p., where OPT is the minimum crossing of any tree. Our greedy analysis extends the traditional one used for set cover. The randomized algorithm rounds a LP relaxation of a corresponding subproblem in stages. 1
DomainIndependent Local Search For Linear Integer Optimization
, 1998
"... Integer and combinatorial optimization problems constitute a major challenge for algorithmics. They arise when a large number of discrete organizational decisions have to be made, subject to constraints and optimization criteria. This thesis ..."
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Cited by 10 (1 self)
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Integer and combinatorial optimization problems constitute a major challenge for algorithmics. They arise when a large number of discrete organizational decisions have to be made, subject to constraints and optimization criteria. This thesis