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72
Collaborative Multiagent Reinforcement Learning by Payoff Propagation
 JOURNAL OF MACHINE LEARNING RESEARCH
, 2006
"... In this article we describe a set of scalable techniques for learning the behavior of a group of agents in a collaborative multiagent setting. As a basis we use the framework of coordination graphs of Guestrin, Koller, and Parr (2002a) which exploits the dependencies between agents to decompose t ..."
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Cited by 64 (2 self)
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In this article we describe a set of scalable techniques for learning the behavior of a group of agents in a collaborative multiagent setting. As a basis we use the framework of coordination graphs of Guestrin, Koller, and Parr (2002a) which exploits the dependencies between agents to decompose the global payoff function into a sum of local terms. First, we deal with the singlestate case and describe a payoff propagation algorithm that computes the individual actions that approximately maximize the global payoff function. The method can be viewed as the decisionmaking analogue of belief propagation in Bayesian networks. Second, we focus on learning the behavior of the agents in sequential decisionmaking tasks. We introduce different modelfree reinforcementlearning techniques, unitedly called Sparse Cooperative Qlearning, which approximate the global actionvalue function based on the topology of a coordination graph, and perform updates using the contribution of the individual agents to the maximal global action value. The combined use of an edgebased decomposition of the actionvalue function and the payoff propagation algorithm for efficient action selection, result in an approach that scales only linearly in the problem size. We provide experimental evidence that our method outperforms related multiagent reinforcementlearning methods based on temporal differences.
Exploiting locality of interaction in factored DecPOMDPs
 In Proc. Int. Joint Conf. Autonomous Agents and Multi Agent Systems
, 2008
"... Decentralized partially observable Markov decision processes (DecPOMDPs) constitute an expressive framework for multiagent planning under uncertainty, but solving them is provably intractable. We demonstrate how their scalability can be improved by exploiting locality of interaction between agents ..."
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Cited by 46 (20 self)
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Decentralized partially observable Markov decision processes (DecPOMDPs) constitute an expressive framework for multiagent planning under uncertainty, but solving them is provably intractable. We demonstrate how their scalability can be improved by exploiting locality of interaction between agents in a factored representation. Factored DecPOMDP representations have been proposed before, but only for DecPOMDPs whose transition and observation models are fully independent. Such strong assumptions simplify the planning problem, but result in models with limited applicability. By contrast, we consider general factored DecPOMDPs for which we analyze the model dependencies over space (locality of interaction) and time (horizon of the problem). We also present a formulation of decomposable value functions. Together, our results allow us to exploit the problem structure as well as heuristics in a single framework that is based on collaborative graphical Bayesian games (CGBGs). A preliminary experiment shows a speedup of two orders of magnitude.
Noncommunicative multirobot coordination in dynamic environments
 Robotics and Autonomous Systems
, 2005
"... Within a group of cooperating agents the decision making of an individual agent depends on the actions of the other agents. In dynamic environments, these dependencies will change rapidly as a result of the continuously changing state. Via a contextspecific decomposition of the problem into smaller ..."
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Cited by 30 (10 self)
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Within a group of cooperating agents the decision making of an individual agent depends on the actions of the other agents. In dynamic environments, these dependencies will change rapidly as a result of the continuously changing state. Via a contextspecific decomposition of the problem into smaller subproblems, coordination graphs offer scalable solutions to the problem of multiagent decision making. In this work, we apply coordination graphs to a continuous (robotic) domain by assigning roles to the agents and then coordinating the different roles. Moreover, we demonstrate that, with some additional assumptions, an agent can predict the actions of the other agents, rendering communication superfluous. We have successfully implemented the proposed method into our UvA Trilearn simulated robot soccer team which won the RoboCup2003 World Championship in
Utile coordination: Learning interdependencies among cooperative agents
 In Proceedings of the IEEE Symposium on Computational Intelligence and Games (CIG’05
, 2005
"... a multiagent system to learn where and how to coordinate. The method starts with uncoordinated learners and maintains statistics on expected returns. Coordination dependencies are dynamically added if the statistics indicate a statistically significant benefit. This results in a compact state repres ..."
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Cited by 29 (0 self)
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a multiagent system to learn where and how to coordinate. The method starts with uncoordinated learners and maintains statistics on expected returns. Coordination dependencies are dynamically added if the statistics indicate a statistically significant benefit. This results in a compact state representation because only necessary coordination is modeled. We apply our method within the framework of coordination graphs in which value rules represent the coordination dependencies between the agents for a specific context. The algorithm is first applied on a small illustrative problem, and next on a large predatorprey problem in which two predators have to capture a single prey. 1
Sparse Cooperative Qlearning
 Proceedings of the International Conference on Machine Learning
, 2004
"... Learning in multiagent systems suffers from the fact that both the state and the action space scale exponentially with the number of agents. In this paper we are interested in using Qlearning to learn the coordinated actions of a group of cooperative agents, using a sparse representation of the joi ..."
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Cited by 26 (6 self)
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Learning in multiagent systems suffers from the fact that both the state and the action space scale exponentially with the number of agents. In this paper we are interested in using Qlearning to learn the coordinated actions of a group of cooperative agents, using a sparse representation of the joint stateaction space of the agents. We first examine a compact representation in which the agents need to explicitly coordinate their actions only in a predefined set of states. Next, we use a coordinationgraph approach in which we represent the Qvalues by value rules that specify the coordination dependencies of the agents at particular states. We show how Qlearning can be efficiently applied to learn a coordinated policy for the agents in the above framework. We demonstrate the proposed method on the predatorprey domain, and we compare it with other related multiagent Qlearning methods.
Anytime Algorithms for Multiagent Decision Making Using Coordination Graphs
 In Proc. Intl. Conf. on Systems, Man and Cybernetics
, 2004
"... Coordination graphs provide a tractable framework for cooperative multiagent decision making by decomposing the global payoff function into a sum of local terms. In this paper we review some distributed algorithms for action selection in a coordination graph and discuss their pros and cons. For real ..."
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Cited by 22 (8 self)
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Coordination graphs provide a tractable framework for cooperative multiagent decision making by decomposing the global payoff function into a sum of local terms. In this paper we review some distributed algorithms for action selection in a coordination graph and discuss their pros and cons. For realtime decision making we emphasize the need for anytime algorithms for action selection: these are algorithms that improve the quality of the solution over time. We describe variable elimination, coordinate ascent, and the maxplus algorithm, the latter being an instance of the belief propagation algorithm in Bayesian networks. We discuss some interesting open problems related to the use of the maxplus algorithm in realtime multiagent decision making.
Incremental Clustering and Expansion for Faster Optimal Planning in Decentralized POMDPs
, 2013
"... This article presents the stateoftheart in optimal solution methods for decentralized partially observable Markov decision processes (DecPOMDPs), which are general models for collaborative multiagent planning under uncertainty. Building off the generalized multiagent A * (GMAA*) algorithm, which ..."
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Cited by 19 (12 self)
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This article presents the stateoftheart in optimal solution methods for decentralized partially observable Markov decision processes (DecPOMDPs), which are general models for collaborative multiagent planning under uncertainty. Building off the generalized multiagent A * (GMAA*) algorithm, which reduces the problem to a tree of oneshot collaborative Bayesian games (CBGs), we describe several advances that greatly expand the range of DecPOMDPs that can be solved optimally. First, we introduce lossless incremental clustering of the CBGs solved by GMAA*, which achieves exponential speedups without sacrificing optimality. Second, we introduce incremental expansion of nodes in the GMAA * search tree, which avoids the need to expand all children, the number of which is in the worst case doubly exponential in the node’s depth. This is particularly beneficial when little clustering is possible. In addition, we introduce new hybrid heuristic representations that are more compact and thereby enable the solution of larger DecPOMDPs. We provide theoretical guarantees that, when a suitable heuristic is used, both incremental clustering and incremental expansion yield algorithms that are both complete and search equivalent. Finally, we present extensive empirical results demonstrating that GMAA*ICE, an algorithm that synthesizes these advances, can optimally solve DecPOMDPs of unprecedented size.
Using the maxplus algorithm for multiagent decision making in coordination graphs
 In RoboCup2005: Robot Soccer World Cup IX
, 2005
"... Abstract. Coordination graphs offer a tractable framework for cooperative multiagent decision making by decomposing the global payoff function into a sum of local terms. Each agent can in principle select an optimal individual action based on a variable elimination algorithm performed on this graph. ..."
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Cited by 14 (4 self)
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Abstract. Coordination graphs offer a tractable framework for cooperative multiagent decision making by decomposing the global payoff function into a sum of local terms. Each agent can in principle select an optimal individual action based on a variable elimination algorithm performed on this graph. This results in optimal behavior for the group, but its worstcase time complexity is exponential in the number of agents, and it can be slow in densely connected graphs. Moreover, variable elimination is not appropriate for realtime systems as it requires that the complete algorithm terminates before a solution can be reported. In this paper, we investigate the maxplus algorithm, an instance of the belief propagation algorithm in Bayesian networks, as an approximate alternative to variable elimination. In this method the agents exchange appropriate payoff messages over the coordination graph, and based on these messages compute their individual actions. We provide empirical evidence that this method converges to the optimal solution for treestructured graphs (as shown by theory), and that it finds near optimal solutions in graphs with cycles, while being much faster than variable elimination. 1
Multiagent Reinforcement Learning for Urban Traffic Control using Coordination Graphs
 Proceedings of the 19th European Conference on Machine Learning
, 2008
"... Abstract. Since traffic jams are ubiquitous in the modern world, optimizing the behavior of traffic lights for efficient traffic flow is a critically important goal. Though most current traffic lights use simple heuristic protocols, more efficient controllers can be discovered automatically via mult ..."
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Cited by 10 (2 self)
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Abstract. Since traffic jams are ubiquitous in the modern world, optimizing the behavior of traffic lights for efficient traffic flow is a critically important goal. Though most current traffic lights use simple heuristic protocols, more efficient controllers can be discovered automatically via multiagent reinforcement learning, where each agent controls a single traffic light. However, in previous work on this approach, agents select only locally optimal actions without coordinating their behavior. This paper extends this approach to include explicit coordination between neighboring traffic lights. Coordination is achieved using the maxplus algorithm, which estimates the optimal joint action by sending locally optimized messages among connected agents. This paper presents the first application of maxplus to a largescale problem and thus verifies its efficacy in realistic settings. It also provides empirical evidence that maxplus performs well on cyclic graphs, though it has been proven to converge only for treestructured graphs. Furthermore, it provides a new understanding of the properties a traffic network must have for such coordination to be beneficial and shows that maxplus outperforms previous methods on networks that possess those properties. Key words: multiagent systems, reinforcement learning, coordination graphs, maxplus, traffic control 1
A statebased programming model and system for wireless sensor networks
 In Proceedings of the 5th International Conference on Pervasive Computing and Communications
, 2007
"... Sensor networks are one important building block towards the realisation of contextaware applications. Suitable communication protocols and middleware solutions are necessary to facilitate the development of sensor network applications. Additionally, the vast number of nodes in sensor networks n ..."
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Cited by 10 (0 self)
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Sensor networks are one important building block towards the realisation of contextaware applications. Suitable communication protocols and middleware solutions are necessary to facilitate the development of sensor network applications. Additionally, the vast number of nodes in sensor networks necessitates a new programming model for application developers. Commonly used programming abstractions force the programmer to express the global behaviour of a network in terms of local actions taken at individual nodes. We argue that global programming abstractions are needed to express global behaviour of a network. We present RuleCaster, a novel statebased programming framework for sensor network applications. RuleCaster provides a highlevel language for application definition, a compiler that splits the highlevel specification into individual tasks and assigns them to the nodes, and a servicebased middleware that provides the interface for collaborative execution of these tasks. 1.