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Region-Based Incremental Pruning for POMDPs  [PDF]
Zhengzhu Feng,Shlomo Zilberstein
Computer Science , 2012,
Abstract: We present a major improvement to the incremental pruning algorithm for solving partially observable Markov decision processes. Our technique targets the cross-sum step of the dynamic programming (DP) update, a key source of complexity in POMDP algorithms. Instead of reasoning about the whole belief space when pruning the cross-sums, our algorithm divides the belief space into smaller regions and performs independent pruning in each region. We evaluate the benefits of the new technique both analytically and experimentally, and show that it produces very significant performance gains. The results contribute to the scalability of POMDP algorithms to domains that cannot be handled by the best existing techniques.
Incremental Pruning: A Simple, Fast, Exact Method for Partially Observable Markov Decision Processes  [PDF]
Anthony R. Cassandra,Michael L. Littman,Nevin Lianwen Zhang
Computer Science , 2013,
Abstract: Most exact algorithms for general partially observable Markov decision processes (POMDPs) use a form of dynamic programming in which a piecewise-linear and convex representation of one value function is transformed into another. We examine variations of the "incremental pruning" method for solving this problem and compare them to earlier algorithms from theoretical and empirical perspectives. We find that incremental pruning is presently the most efficient exact method for solving POMDPs.
Pruning based incremental construction of concept lattice
基于剪枝的概念格渐进式构造

HU Li-hua,ZHANG Ji-fu,ZHANG Su-lan,
胡立华
,张继福,张素兰

计算机应用 , 2006,
Abstract: Concept lattice is the core data structure of formal concept analysis.However,with the sharp increasing of the data to deal with and analyze,its construction efficiency became the key problem.An incremental algorithm PCL of constructing concept lattice based on pruning was presented through eliminating the redundancy information in the construction process by pruning.It decreased the comparative amount of the intent of concept lattice and improved the efficiency of the concept lattice's construction.The experiment results prove the correctness and validity of PCL by taking the celestial spectrum data as the formal context.
Incremental construction algorithm of constrained concept lattice based on pruning
基于剪枝的约束概念格的渐进式构造算法

MA Yang,ZHANG Ji-fu,ZHANG Su-lan,
马洋
,张继福,张素兰

计算机应用 , 2009,
Abstract: An incremental construction algorithm named PCCL of the constrained concept lattice was presented by using pruning technology that eliminated the redundant information in the construction process. By making use of the rigorous monotone relation between father concept's intent and child concept's intent, all nodes of the constrained concept lattice were scanned from top to down, and the comparative operations between the intents were decreased, thus the efficiency of constructing the constrained concept lattice was improved. Experimental results verify the correctness and validity of PCCL by taking the celestial spectrum data as the formal context.
Distribution over Beliefs for Memory Bounded Dec-POMDP Planning  [PDF]
Gabriel Corona,Francois Charpillet
Computer Science , 2012,
Abstract: We propose a new point-based method for approximate planning in Dec-POMDP which outperforms the state-of-the-art approaches in terms of solution quality. It uses a heuristic estimation of the prior probability of beliefs to choose a bounded number of policy trees: this choice is formulated as a combinatorial optimisation problem minimising the error induced by pruning.
Hybrid BDI-POMDP Framework for Multiagent Teaming  [PDF]
R. Nair,M. Tambe
Computer Science , 2011, DOI: 10.1613/jair.1549
Abstract: Many current large-scale multiagent team implementations can be characterized as following the belief-desire-intention (BDI) paradigm, with explicit representation of team plans. Despite their promise, current BDI team approaches lack tools for quantitative performance analysis under uncertainty. Distributed partially observable Markov decision problems (POMDPs) are well suited for such analysis, but the complexity of finding optimal policies in such models is highly intractable. The key contribution of this article is a hybrid BDI-POMDP approach, where BDI team plans are exploited to improve POMDP tractability and POMDP analysis improves BDI team plan performance. Concretely, we focus on role allocation, a fundamental problem in BDI teams: which agents to allocate to the different roles in the team. The article provides three key contributions. First, we describe a role allocation technique that takes into account future uncertainties in the domain; prior work in multiagent role allocation has failed to address such uncertainties. To that end, we introduce RMTDP (Role-based Markov Team Decision Problem), a new distributed POMDP model for analysis of role allocations. Our technique gains in tractability by significantly curtailing RMTDP policy search; in particular, BDI team plans provide incomplete RMTDP policies, and the RMTDP policy search fills the gaps in such incomplete policies by searching for the best role allocation. Our second key contribution is a novel decomposition technique to further improve RMTDP policy search efficiency. Even though limited to searching role allocations, there are still combinatorially many role allocations, and evaluating each in RMTDP to identify the best is extremely difficult. Our decomposition technique exploits the structure in the BDI team plans to significantly prune the search space of role allocations. Our third key contribution is a significantly faster policy evaluation algorithm suited for our BDI-POMDP hybrid approach. Finally, we also present experimental results from two domains: mission rehearsal simulation and RoboCupRescue disaster rescue simulation.
Evaluating the impact of MEDLINE filters on evidence retrieval: study protocol
Salimah Z Shariff, Meaghan S Cuerden, R Brian Haynes, K Ann McKibbon, Nancy L Wilczynski, Arthur V Iansavichus, Mark R Speechley, Amardeep Thind, Amit X Garg
Implementation Science , 2010, DOI: 10.1186/1748-5908-5-58
Abstract: When a physician searches MEDLINE, we hypothesize the use of filters will increase the number of relevant articles retrieved (increase 'recall,' also called sensitivity) and decrease the number of non-relevant articles retrieved (increase 'precision,' also called positive predictive value), compared to the performance of a physician's search unaided by filters.We will survey a random sample of 100 nephrologists in Canada to obtain the MEDLINE search that they would first perform themselves for a focused clinical question. Each question we provide to a nephrologist will be based on the topic of a recently published, well-conducted systematic review. We will examine the performance of a physician's unaided MEDLINE search. We will then apply a total of eight filter combinations to the search (filters used in isolation or in combination). We will calculate the recall and precision of each search. The filter combinations that most improve on unaided physician searches will be identified and characterized.If these filters improve search performance, physicians will be able to search MEDLINE for renal evidence more effectively, in less time, and with less frustration. Additionally, our methodology can be used as a proof of concept for the evaluation of search filters in other disciplines.We live in the information age, and the practice of medicine is increasingly complex and specialized. The conclusion that medical professionals have unmet information needs is inescapable[1-6]. Studies confirm opportunities to improve patient care[7-12]. Unfortunately, physicians are often unaware of new clinically relevant information and frequently report the need for supplementary information for patient encounters[13-17]. The amount of useful knowledge continues to grow, and is greater than any one practitioner can easily retain. Over the last decade, the MEDLINE database grew by over seven million citations, to 18 million citations[18-20] (as of May 2010). About 2,000 to 4,000 new ref
Penetration Testing == POMDP Solving?  [PDF]
Carlos Sarraute,Olivier Buffet,Joerg Hoffmann
Computer Science , 2013,
Abstract: Penetration Testing is a methodology for assessing network security, by generating and executing possible attacks. Doing so automatically allows for regular and systematic testing without a prohibitive amount of human labor. A key question then is how to generate the attacks. This is naturally formulated as a planning problem. Previous work (Lucangeli et al. 2010) used classical planning and hence ignores all the incomplete knowledge that characterizes hacking. More recent work (Sarraute et al. 2011) makes strong independence assumptions for the sake of scaling, and lacks a clear formal concept of what the attack planning problem actually is. Herein, we model that problem in terms of partially observable Markov decision processes (POMDP). This grounds penetration testing in a well-researched formalism, highlighting important aspects of this problem's nature. POMDPs allow to model information gathering as an integral part of the problem, thus providing for the first time a means to intelligently mix scanning actions with actual exploits.
Discretized Approximations for POMDP with Average Cost  [PDF]
Huizhen Yu,Dimitri Bertsekas
Mathematics , 2012,
Abstract: In this paper, we propose a new lower approximation scheme for POMDP with discounted and average cost criterion. The approximating functions are determined by their values at a finite number of belief points, and can be computed efficiently using value iteration algorithms for finite-state MDP. While for discounted problems several lower approximation schemes have been proposed earlier, ours seems the first of its kind for average cost problems. We focus primarily on the average cost case, and we show that the corresponding approximation can be computed efficiently using multi-chain algorithms for finite-state MDP. We give a preliminary analysis showing that regardless of the existence of the optimal average cost J in the POMDP, the approximation obtained is a lower bound of the liminf optimal average cost function, and can also be used to calculate an upper bound on the limsup optimal average cost function, as well as bounds on the cost of executing the stationary policy associated with the approximation. Weshow the convergence of the cost approximation, when the optimal average cost is constant and the optimal differential cost is continuous.
A Method for Speeding Up Value Iteration in Partially Observable Markov Decision Processes  [PDF]
Nevin Lianwen Zhang,Stephen S. Lee,Weihong Zhang
Computer Science , 2013,
Abstract: We present a technique for speeding up the convergence of value iteration for partially observable Markov decisions processes (POMDPs). The underlying idea is similar to that behind modified policy iteration for fully observable Markov decision processes (MDPs). The technique can be easily incorporated into any existing POMDP value iteration algorithms. Experiments have been conducted on several test problems with one POMDP value iteration algorithm called incremental pruning. We find that the technique can make incremental pruning run several orders of magnitude faster.
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