Publications (87)17.13 Total impact
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ABSTRACT: Crowdsourcing applications frequently employ many individual workers, each performing a small amount of work. In such settings, individually determining the reward for each assignment and worker may seem economically beneficial, but is inapplicable if manually performed. We thus consider the problem of designing automated agents for automatic reward determination and negotiation in such settings. We formally describe this problem and show that it is NPhard. We therefore present two automated agents for the problem, based on two different models of human behavior. The first, the Reservation Price Based Agent (RPBA), is based on the concept of a RP, and the second, the No Bargaining Agent (NBA) which tries to avoid any negotiation. The performance of the agents is tested in extensive experiments with real human subjects, where both NBA and RPBA outperform strategies developed by human experts.Autonomous Agents and MultiAgent Systems 01/2013; · 0.79 Impact Factor  [show abstract] [hide abstract]
ABSTRACT: We consider a setting in which a single divisible good ("cake") needs to be divided between n players, each with a possibly di?fferent valuation function over pieces of the cake. For this setting, we address the problem of ?finding divisions that maximize the social welfare, focusing on divisions where each player needs to get one contiguous piece of the cake. We show that for both the utilitarian and the egalitarian social welfare functions it is NPhard to find the optimal division. For the utilitarian welfare, we provide a constant factor approximation algorithm, and prove that no FPTAS is possible unless P=NP. For egalitarian welfare, we prove that it is NPhard to approximate the optimum to any factor smaller than 2. For the case where the number of players is small, we provide an FPT (fixed parameter tractable) FPTAS for both the utilitarian and the egalitarian welfare objectives.05/2012;  [show abstract] [hide abstract]
ABSTRACT: We introduce a generalization of interval graphs, which we call dotted interval graphs (DIG). A dotted interval graph is an intersection graph of arithmetic progressions (=dotted intervals). Coloring of dotted intervals graphs naturally arises in the context of high throughput genotyping. We study the properties of dotted interval graphs, with a focus on coloring. We show that any graph is a DIG but that DIG d graphs, i.e. DIGs in which the arithmetic progressions have a jump of at most d, form a strict hierarchy. We show that coloring DIG d graphs is NPcomplete even for d = 2. For any fixed d, we provide a 7 8 d approximation for the coloring of DIG d graphs.ACM Transactions on Algorithms  TALG. 01/2012; 
Article: Throw One's Cake  and Have It Too
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ABSTRACT: We consider the problem of fairly dividing a heterogeneous cake between a number of players with different tastes. In this setting, it is known that fairness requirements may result in a suboptimal division from the social welfare standpoint. Here, we show that in some cases, discarding some of the cake and fairly dividing only the remainder may be socially preferable to any fair division of the entire cake. We study this phenomenon, providing asymptoticallytight bounds on the social improvement achievable by such discarding.Computing Research Repository  CORR. 01/2011; 
Conference Proceeding: Throw One's Cake  and Eat It Too.
Algorithmic Game Theory, 4th International Symposium, SAGT 2011, Amalfi, Italy, October 1719, 2011. Proceedings; 01/2011 
Article: Finding witnesses by peeling.
ACM Transactions on Algorithms. 01/2011; 7:24. 
Conference Proceeding: On agent types in coalition formation problems.
9th International Conference on Autonomous Agents and Multiagent Systems (AAMAS 2010), Toronto, Canada, May 1014, 2010, Volume 13; 01/2010 
Conference Proceeding: The Efficiency of Fair Division with Connected Pieces.
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ABSTRACT: We consider the issue of fair division of goods, using the cake cutting abstraction, and aim to bound the possible degradation in social welfare due to the fairness requirements. Previous work has considered this problem for the setting where the division may allocate each player any number of unconnected pieces. Here, we consider the setting where each player must receive a single connected piece. For this setting, we provide tight bounds on the maximum possible degradation to both utilitarian and egalitarian welfare due to three fairness criteria — proportionality, envyfreeness and equitability.Internet and Network Economics  6th International Workshop, WINE 2010, Stanford, CA, USA, December 1317, 2010. Proceedings; 01/2010 
Conference Proceeding: Pareto Efficiency and Approximate Pareto Efficiency in Routing and Load Balancing Games.
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ABSTRACT: We analyze the Pareto efficiency, or inefficiency, of solutions to routing games and load balancing games, focusing on Nash equilibria and greedy solutions to these games. For some settings, we show that the solutions are necessarily Pareto optimal. When this is not the case, we provide a measure to quantify the distance of the solution from Pareto efficiency. Using this measure, we provide upper and lower bounds on the “Pareto inefficiency” of the different solutions. The settings we consider include load balancing games on identical, uniformlyrelated, and unrelated machines, both using pure and mixed strategies, and nonatomic routing in general and some specific networks.Algorithmic Game Theory  Third International Symposium, SAGT 2010, Athens, Greece, October 1820, 2010. Proceedings; 01/2010  J. Comput. Syst. Sci. 01/2009; 75:359370.
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ABSTRACT: Historically, approximate pattern matching has mainly focused at coping with errors in the data, while the order of the text/pattern was assumed to be more or less correct. In this paper we consider a class of pattern matching problems where the content is assumed to be correct, while the locations may have shifted/changed. We formally define a broad class of problems of this type, capturing situations in which the pattern is obtained from the text by a sequence of rearrangements. We consider several natural rearrangement schemes, including the analogues of the ℓ1 and ℓ2 distances, as well as two distances based on interchanges. For these, we present efficient algorithms to solve the resulting string matching problems.Journal of Computer and System Sciences. 01/2009;  Theor. Comput. Sci. 01/2009; 410:53345346.

Conference Proceeding: Easy and hard coalition resource game formation problems: a parameterized complexity analysis.
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ABSTRACT: Coalition formation is a key topic in multiagent systems (mas). Coalitions enable agents to achieve goals that they may not have been able to achieve independently, and en courages resource sharing among agents with different goals. A range of previous studies have found that problems in coalitional games tend to be computationally complex. However, such hardness results consider the entire input as one, ignoring any structural information on the instances. In the case of coalition formation problems, this bundles to gether several distinct elements of the input, e.g. the agent set, the goal set, the resources, etc. In this paper we re examine the complexity of coalition formation problems in the coalition resources game model, as a function of their distinct input elements, using the theory of parameterized complexity. The analysis shows that not all parts of the in put are created equal, and that many instances of the prob lem are actually tractable. We show that the problems are FPT in the number of goals, implying that if the number of goals is bounded then an efficient algorithm is available. Similarly, the problems are FPT in the combination of the number of agents and resources, again implying that if these parameters are bounded, then an efficient algorithm is avail able. On the other hand, the problems are para NP hard in the number of resources, implying that even if we bound the number of resources the problems (probably) remain hard. Additionally, we show that most problems are W(1)hard in the size of the coalition of interest, indicating that there is (probably) no algorithm polynomial in all but the coalition size. The exact definitions of the parameterized complexity notions FPT, Para NP and W(1) are provided herein.8th International Joint Conference on Autonomous Agents and Multiagent Systems (AAMAS 2009), Budapest, Hungary, May 1015, 2009, Volume 1; 01/2009  [show abstract] [hide abstract]
ABSTRACT: Recently, a new pattern matching paradigm was proposed, pattern matching with address errors. In this paradigm approximate string matching problems are studied, where the content is unaltered and only the locations of the different entries may change. Specifically, a broad class of problems was definedthe class of rearrangement errors. In this type of error the pattern is transformed through a sequence of rearrangement operations, each with an associated cost. The natural @?"1 and @?"2 rearrangement systems were considered. The best algorithm presented for general patterns, that may have repeating symbols, is O(nm). In this paper, we show that the problem can be approximated in linear time for general patterns! Another natural rearrangement system is considered in this paperthe @?"~ rearrangement distance. For this new rearrangement system efficient exact solutions for different variants of the problem are provided, as well as a faster approximation.Theoretical Computer Science 01/2009; 410(43):43824390. · 0.49 Impact Factor 
Article: Efficient computations of
Theor. Comput. Sci. 01/2009; 410:43824390. 
Conference Proceeding: Collaborative Multi Agent Physical Search with Probabilistic Knowledge.
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ABSTRACT: This paper considers the setting wherein a group of agents (e.g., robots) is seeking to obtain a given tan gible good, potentially available at different loca tions in a physical environment. Traveling between locations, as well as acquiring the good at any given location consumes from the resources available to the agents (e.g., battery charge). The availability of the good at any given location, as well as the ex act cost of acquiring the good at the location is not fully known in advance, and observed only upon physically arriving at the location. However, a priori probabilities on the availability and poten tial cost are provided. Given such as setting, the problem is to find a strategy/plan that maximizes the probability of acquiring the good while mini mizing resource consumption. Sample applications include agents in exploration and patrol missions, e.g., rovers on Mars seeking to mine a specific min eral. Although this model captures many real world scenarios, it has not been investigated so far. We focus on the case where locations are aligned along a path, and study several variants of the prob lem, analyzing the effects of communication and coordination. For the case that agents can com municate, we present a polynomial algorithm that works for any fixed number of agents. For non communicating agents, we present a polynomial al gorithm that is suitable for any number of agents. Finally, we analyze the difference between homo geneous and heterogeneous agents, both with re spect to their allotted resources and with respect to their capabilities.IJCAI 2009, Proceedings of the 21st International Joint Conference on Artificial Intelligence, Pasadena, California, USA, July 1117, 2009; 01/2009 
Conference Proceeding: Quasidistinct Parsing and Optimal Compression Methods.
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ABSTRACT: In this paper, the optimality proof of LempelZiv coding is restudied, and a much more general compression optimality theorem is derived. In particular, the property of quasidistinct parsing is defined. This property is much weaker than distinct parsing required in the original proof, yet we show that the theorem holds with this weaker property as well. This provides a better understanding of the optimality proof of LempelZiv coding, together with a new tool for proving optimality of other compression schemes. To demonstrate the possible use of this generalization, a new coding method – the APT coding – is presented. This new coding method is based on a principle that is very different from LempelZiv’s coding. Moreover, it does not directly define any parsing technique. Nevertheless, APT coding is analyzed in this paper and using the generalized theorem shown to be asymptotically optimal up to a constant factor, if APT quasidistinctness hypothesis holds. An empirical evidence that this hypothesis holds is also given.Combinatorial Pattern Matching, 20th Annual Symposium, CPM 2009, Lille, France, June 2224, 2009, Proceedings; 01/2009  [show abstract] [hide abstract]
ABSTRACT: A string S ∈ Σ m can be viewed as a set of pairs S = { (σ i , i) : i ∈ { 0,..., m − 1} }. We consider approximate pattern matching problems arising from the setting where errors are introduced to the location component (i), rather than the more traditional setting, where errors are introduced to the content itself (σ i ). In this paper, we consider the case where bits of i may be erroneously flipped, either in a consistent or transient manner. We formally define the corresponding approximate pattern matching problems, and provide efficient algorithms for their resolution, while introducing some novel techniques.06/2008: pages 118129; 
Conference Proceeding: Evaluation of election outcomes under uncertainty.
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ABSTRACT: We investigate the extent to which it is possible to evaluate the probability of a particular candidate winning an elec tion, given imperfect information about the preferences of the electorate. We assume that for each voter, we have a probability distribution over a set of preference orderings. Thus, for each voter, we have a number of possible prefer ence orderings { we do not know which of these orderings actually represents the voters' preferences, but we know for each one the probability that it does. We give a polynomial algorithm to solve the problem of computing the probability that a given candidate will win when the number of candi dates is a constant. However, when the number of candi dates is not bounded, we prove that the problem becomes #PHard for the Plurality, Borda, and Copeland voting pro tocols. We further show that even evaluating if a candidate has any chance to win is NPComplete for the Plurality vot ing protocol, in the weighted voters case. We give a poly nomial algorithm for this problem when the voters' weights are equal.7th International Joint Conference on Autonomous Agents and Multiagent Systems (AAMAS 2008), Estoril, Portugal, May 1216, 2008, Volume 2; 01/2008 
Conference Proceeding: Physical Search Problems Applying Economic Search Models.
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ABSTRACT: This paper considers the problem of an agent searching for a resource or a tangible good in a physical environment, where at each stage of its search it observes one source where this good can be found. The cost of acquiring the resource or good at a given source is uncertain (apriori), and the agent can observe its true value only when physically arriving at the source. Sample applications involving this type of search in clude agents in exploration and patrol missions (e.g., an agent seeking to find the best location to deploy sensing equipment along its path). The uniqueness of these settings is that the expense of observing the source on each step of the process derives from the last source the agent explored. We ana lyze three variants of the problem, differing in their objec tive: minimizing the total expected cost, maximizing the suc cess probability given an initial budget, and minimizing the budget necessary to obtain a given success probability. For each variant, we first introduce and analyze the problem with a single agent, either providing a polynomial solution to the problem or proving it is NPComplete. We also introduce an innovative fully polynomial time approximation scheme al gorithm for the minimum budget variant. Finally, the results for the single agent case are generalized to multiagent set tings.Proceedings of the TwentyThird AAAI Conference on Artificial Intelligence, AAAI 2008, Chicago, Illinois, USA, July 1317, 2008; 01/2008
Publication Stats
937  Citations  
17.13  Total Impact Points  
Top Journals
Institutions

1970–2013

Bar Ilan University
 Department of Computer Science
Gan, Tel Aviv, Israel


2006–2007

Technion  Israel Institute of Technology
H̱efa, Haifa District, Israel


2003

CUNY Graduate Center
New York City, New York, United States


1992–1994

Hebrew University of Jerusalem
Yerushalayim, Jerusalem District, Israel


1993

Weizmann Institute of Science
Israel
