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48
Selfish Caching in Distributed Systems: A GameTheoretic Analysis
 in Proc. ACM Symposium on Principles of Distributed Computing (ACM PODC
, 2004
"... We analyze replication of resources by server nodes that act selfishly, using a gametheoretic approach. We refer to this as the selfish caching problem. In our model, nodes incur either cost for replicating resources or cost for access to a remote replica. We show the existence of pure strategy Nas ..."
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Cited by 62 (2 self)
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We analyze replication of resources by server nodes that act selfishly, using a gametheoretic approach. We refer to this as the selfish caching problem. In our model, nodes incur either cost for replicating resources or cost for access to a remote replica. We show the existence of pure strategy Nash equilibria and investigate the price of anarchy, which is the relative cost of the lack of coordination. The price of anarchy can be high due to undersupply problems, but with certain network topologies it has better bounds. With a payment scheme the game can always implement the social optimum in the best case by giving servers incentive to replicate.
The PrizeCollecting Generalized Steiner Tree Problem Via A New Approach Of PrimalDual Schema
"... In this paper we study the prizecollecting version of the Generalized Steiner Tree problem. To the best of our knowledge, there is no general combinatorial technique in approximation algorithms developed to study the prizecollecting versions of various problems. These problems are studied on a cas ..."
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Cited by 45 (13 self)
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In this paper we study the prizecollecting version of the Generalized Steiner Tree problem. To the best of our knowledge, there is no general combinatorial technique in approximation algorithms developed to study the prizecollecting versions of various problems. These problems are studied on a case by case basis by Bienstock et al. [5] by applying an LProunding technique which is not a combinatorial approach. The main contribution of this paper is to introduce a general combinatorial approach towards solving these problems through novel primaldual schema (without any need to solve an LP). We fuse the primaldual schema with Farkas lemma to obtain a combinatorial 3approximation algorithm for the PrizeCollecting Generalized Steiner Tree problem. Our work also inspires a combinatorial algorithm [12] for solving a special case of Kelly’s problem [21] of pricing edges. We also consider the kforest problem, a generalization of kMST and kSteiner tree, and we show that in spite of these problems for which there are constant factor approximation algorithms, the kforest problem is much harder to approximate. In particular, obtaining an approximation factor better than O(n 1/6−ε) for kforest requires substantially new ideas including improving the approximation factor O(n 1/3−ε) for the notorious densest ksubgraph problem. We note that kforest and prizecollecting version of Generalized Steiner Tree are closely related to each other, since the latter is the Lagrangian relaxation of the former.
On the Value of Coordination in Network Design
"... We study network design games where n selfinterested agents have to form a network by purchasing links from a given set of edges. We consider Shapley cost sharing mechanisms that split the cost of an edge in a fair manner among the agents using the edge. It is well known that the price of anarchy o ..."
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Cited by 36 (0 self)
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We study network design games where n selfinterested agents have to form a network by purchasing links from a given set of edges. We consider Shapley cost sharing mechanisms that split the cost of an edge in a fair manner among the agents using the edge. It is well known that the price of anarchy of these games is as high as n. Therefore, recent research has focused on evaluating the price of stability, i.e. the cost of the best Nash equilibrium relative to the social optimum. In this paper we investigate to which extent coordination among agents can improve the quality of solutions. We resort to the concept of strong Nash equilibria, which were introduced by Aumann and are resilient to deviations by coalitions of agents. We analyze the price of anarchy of strong Nash equilibria and develop lower and upper bounds for unweighted and weighted games in both directed and undirected graphs. These bounds are tight or nearly tight for many scenarios. It shows that using coordination, the price of anarchy drops from linear to logarithmic bounds. We complement these results by also proving the first superconstant lower bound on the price of stability of standard equilibria (without coordination) in undirected graphs. More specifically, we show a lower bound of Ω(log W / log log W) for weighted games, where W is the total weight of all the agents. This almost matches the known upper bound of O(log W). Our results imply that, for most settings, the worstcase performance ratios of strong coordinated equilibria are essentially always as good as the performance ratios of the best equilibria achievable without coordination. These settings include unweighted games in directed graphs as well as weighted games in both directed and undirected graphs.
Beyond Moulin Mechanisms
"... The only known general technique for designing truthful, approximately budgetbalanced costsharing mechanisms is due to Moulin. While Moulin mechanisms have been successfully designed for a wide range of applications, recent negative results show that for many fundamental costsharing problems, Mou ..."
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Cited by 27 (5 self)
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The only known general technique for designing truthful, approximately budgetbalanced costsharing mechanisms is due to Moulin. While Moulin mechanisms have been successfully designed for a wide range of applications, recent negative results show that for many fundamental costsharing problems, Moulin mechanisms inevitably suffer from poor budgetbalance, poor economic efficiency, or both. We propose acyclic mechanisms, a new framework for designing truthful, approximately budgetbalanced costsharing mechanisms. Acyclic mechanisms strictly generalize Moulin mechanisms and offer three important advantages. First, it is easier to design acyclic mechanisms than Moulin mechanisms: many classical primaldual algorithms naturally induce a nonMoulin acyclic mechanism with good performance guarantees. Second, for several important classes of costsharing problems, acyclic mechanisms have exponentially better budgetbalance and economic efficiency than Moulin mechanisms. Finally, while Moulin mechanisms have found application primarily in binary demand games, we extend acyclic mechanisms to general demand games, a multiparameter setting in which each bidder can be allocated one of several levels of service.
Collaboration and Shared Plans in the Open World: Studies of Ridesharing
"... We develop and test computational methods for guiding collaboration that demonstrate how shared plans can be created in realworld settings, where agents can be expected to have diverse and varying goals, preferences, and availabilities. The methods are motivated and evaluated in the realm of ridesh ..."
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Cited by 26 (1 self)
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We develop and test computational methods for guiding collaboration that demonstrate how shared plans can be created in realworld settings, where agents can be expected to have diverse and varying goals, preferences, and availabilities. The methods are motivated and evaluated in the realm of ridesharing, using GPS logs of commuting data. We consider challenges with coordination among selfinterested people aimed at minimizing the cost of transportation and the impact of travel on the environment. We present planning, optimization, and payment mechanisms that provide fair and efficient solutions to the rideshare collaboration challenge. We evaluate different VCGbased payment schemes in terms of their computational efficiency, budget balance, incentive compatibility, and strategy proofness. We present the behavior and analyses provided by the ABC ridesharing prototype system. The system learns about destinations and preferences from GPS traces and calendars, and considers time, fuel, environmental, and cognitive costs. We review how ABC generates rideshare plans from hundreds of reallife GPS traces collected from a community of commuters and reflect about the promise of employing the ABC methods to reduce the number of vehicles on the road, thus reducing CO2 emissions and fuel expenditures. 1
Crossmonotonic costsharing methods for connected facility location
 In Proceedings of the 5th ACM Conference on Electronic Commerce (EC
, 2004
"... We devise cost sharing methods for connected facility location games that are crossmonotonic, competitive and recover a constant fraction of the optimal cost. The novelty of this work is that we use randomized algorithms and that we share the expected cost among the participating users. We also pro ..."
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Cited by 17 (0 self)
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We devise cost sharing methods for connected facility location games that are crossmonotonic, competitive and recover a constant fraction of the optimal cost. The novelty of this work is that we use randomized algorithms and that we share the expected cost among the participating users. We also provide a primaldual cost sharing method for the connected facility location game with opening costs.
Towards truthful mechanisms for binary demand games: a general framework
 In Proceedings of the 6th ACM conference on Electronic commerce
, 2005
"... The family of VickreyClarkeGroves (VCG) mechanisms is arguably the most celebrated achievement in truthful mechanism design. However, VCG mechanisms have their limitations. They only apply to optimization problems with a utilitarian objective function, and their output should optimize the objectiv ..."
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Cited by 17 (10 self)
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The family of VickreyClarkeGroves (VCG) mechanisms is arguably the most celebrated achievement in truthful mechanism design. However, VCG mechanisms have their limitations. They only apply to optimization problems with a utilitarian objective function, and their output should optimize the objective function. For many optimization problems, finding the optimal output is computationally intractable. If we apply VCG mechanisms to polynomialtime algorithms that approximate the optimal solution, the resulting mechanisms may no longer be truthful. In light of these limitations, it is useful to study whether we can design a truthful nonVCG payment scheme that is computationally tractable for a given output method O. In this paper, we focus our attention on binary demand games in which the agents’ only available actions are to take part in the a game or not to. For these problems, we prove that a truthful mechanism M = (O, P) exists (with proper payment method P) if and only if O satisfies a certain monotone property. We also provide several general algorithms to compute the payments efficiently for various types of output. In particular, we show how a truthful payment can be computed through “or/and ” combinations, roundbased combinations, and some more complex combinations of outputs from subgames.
Cost Sharing and Strategyproof Mechanisms for Set Cover Games
"... We develop for set cover games several general costsharing methods that are approximately budgetbalanced, core, and/or groupstrategyproof. We first study the cost sharing for a single set cover game, which does not have a budgetbalanced core. We show that there is no cost allocation method that ..."
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Cited by 13 (3 self)
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We develop for set cover games several general costsharing methods that are approximately budgetbalanced, core, and/or groupstrategyproof. We first study the cost sharing for a single set cover game, which does not have a budgetbalanced core. We show that there is no cost allocation method that can of the total cost if we require the cost sharing being a core. Here n is the number of all players to be served. We give an efficient cost 1 allocation method that always recovers of the total cost, where dmax is ln dmax the maximum size of all sets. We then study the cost allocation scheme for all induced subgames. It is known that no cost sharing scheme can always recover more than 1 of the total cost for every subset of players. We give an efficient cost n sharing scheme that always recovers at least 1 of the total cost for every subset 2n of players and furthermore, our scheme is crossmonotone. When the elements to be covered are selfish agents with privately known valuations, we present a strategyproof charging mechanism, under the assumption that all sets are simple sets, such that each element maximizes its profit when it reports its valuation truthfully; further, the total cost of the set cover is no more than ln dmax times that of an optimal solution. When the sets are selfish agents with privately known costs, we present a strategyproof payment mechanism in which each set maximizes its profit when it reports its cost truthfully. We also show how to fairly share the payments to all sets among the elements. always recover more than 1 ln n 1
Optimal efficiency guarantees for network design mechanisms
 IN PROCEEDINGS OF THE 12TH CONFERENCE ON INTEGER PROGRAMMING AND COMBINATORIAL OPTIMIZATION (IPCO), VOLUME 4513 OF LECTURE NOTES IN COMPUTER SCIENCE
, 2007
"... A costsharing problem is defined by a set of players vying to receive some good or service, and a cost function describing the cost incurred by the auctioneer as a function of the set of winners. A costsharing mechanism is a protocol that decides which players win the auction and at what prices. ..."
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Cited by 12 (1 self)
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A costsharing problem is defined by a set of players vying to receive some good or service, and a cost function describing the cost incurred by the auctioneer as a function of the set of winners. A costsharing mechanism is a protocol that decides which players win the auction and at what prices. Three desirable but provably mutually incompatible properties of a costsharing mechanism are: incentivecompatibility, meaning that players are motivated to bid their true private value for receiving the good; budgetbalance, meaning that the mechanism recovers its incurred cost with the prices charged; and efficiency, meaning that the cost incurred and the value to the players served are traded off in an optimal way. Our work is motivated by the following fundamental question: for which costsharing problems are incentivecompatible mechanisms with good approximate budgetbalance and efficiency possible? We focus on cost functions defined implicitly by NPhard combinatorial optimization problems, including the metric uncapacitated facility location problem, the Steiner tree problem, and rentorbuy network design problems. For facility location and rentorbuy network design, we establish for the first time that approximate budgetbalance and efficiency are simultaneously possible. For the Steiner tree problem, where such a guarantee was previously known, we prove a new, optimal lower bound on the approximate efficiency achievable by the wide and natural class of “Moulin mechanisms”. This lower bound exposes a latent approximation hierarchy among different costsharing problems.
Quantifying Inefficiency in CostSharing Mechanisms
, 2009
"... In a costsharing problem, several participants with unknown preferences vie to receive some good or service, and each possible outcome has a known cost. A costsharing mechanism is a protocol that decides which participants are allocated a good and at what prices. Three desirable properties of a co ..."
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Cited by 12 (1 self)
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In a costsharing problem, several participants with unknown preferences vie to receive some good or service, and each possible outcome has a known cost. A costsharing mechanism is a protocol that decides which participants are allocated a good and at what prices. Three desirable properties of a costsharing mechanism are: incentivecompatibility, meaning that participants are motivated to bid their true private value for receiving the good; budgetbalance, meaning that the mechanism recovers its incurred cost with the prices charged; and economic efficiency, meaning that the cost incurred and the value to the participants are traded off in an optimal way. These three goals have been known to be mutually incompatible for thirty years. Nearly all the work on costsharing mechanism design by the economics and computer science communities has focused on achieving two of these goals while completely ignoring the third. We introduce novel measures for quantifying efficiency loss in costsharing mechanisms and prove simultaneous approximate budgetbalance and approximate efficiency guarantees for mechanisms for a wide range of costsharing problems, including all submodular and Steiner tree problems. Our key technical tool is an exact characterization of worstcase efficiency loss in Moulin mechanisms, the dominant paradigm in costsharing mechanism design.