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2014  
[24] 
2014. Optimal Scheduling for Replacing Perimeter Guarding Unmanned Aerial Vehicles. Technical Report.
In series: LiTHMATR #2014:09. Linköping University Electronic Press. 14 pages. Guarding the perimeter of an area in order to detect potential intruders is an important task in a variety of securityrelated applications. This task can in many circumstances be performed by a set of cameraequipped unmanned aerial vehicles (UAVs). Such UAVs will occasionally require refueling or recharging, in which case they must temporarily be replaced by other UAVs in order to maintain complete surveillance of the perimeter. In this paper we consider the problem of scheduling such replacements. We present optimal replacement strategies and justify their optimality. 
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[23] 
2014. Local Search for Hopconstrained Directed Steiner Tree Problem with Application to UAVbased Multitarget Surveillance. Technical Report.
In series: LiTHMATR #2014:10. Linköping University Electronic Press. 26 pages. We consider the directed Steiner tree problem (DSTP) with a constraint on the total number of arcs (hops) in the tree. This problem is known to be NPhard, and therefore, only heuristics can be applied in the case of its largescale instances. For the hopconstrained DSTP, we propose local search strategies aimed at improving any heuristically produced initial Steiner tree. They are based on solving a sequence of hopconstrained shortest path problems for which we have recently developed ecient label correcting algorithms. The presented approach is applied to nding suitable 3D locations where unmanned aerial vehicles (UAVs) can be placed to relay information gathered in multitarget monitoring and surveillance. The eciency of our algorithms is illustrated by results of numerical experiments involving problem instances with up to 40 000 nodes and up to 20 million arcs. 
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2012  
[22] 
2012. Proceedings of the 20th European Conference on Artificial Intelligence (ECAI). Conference Proceedings.
In series: Frontiers in Artificial Intelligence and Applications #242. IOS Press. 1056 pages. ISBN: 9781614990970. 
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2009  
[21] 
2009. Optimal placement of communications relay nodes. Technical Report.
In series: LiTHMATR #2009:3. Linköpings universitet. 21 pages. We consider a constrained optimization problem with mixed integer and real variables. It models optimal placement of communications relay nodes in the presence of obstacles. This problem is widely encountered, for instance, in robotics, where it is required to survey some target located in one point and convey the gathered information back to a base station located in another point. One or more unmanned aerial or ground vehicles (UAVs or UGVs) can be used for this purpose as communications relays. The decision variables are the number of unmanned vehicles (UVs) and the UV positions. The objective function is assumed to access the placement quality. We suggest one instance of such a function which is more suitable for accessing UAV placement. The constraints are determined by, firstly, a free line of sight requirement for every consecutive pair in the chain and, secondly, a limited communication range. Because of these requirements, our constrained optimization problem is a difficult multiextremal problem for any fixed number of UVs. Moreover, the feasible set of real variables is typically disjoint. We present an approach that allows us to efficiently find a practically acceptable approximation to a global minimum in the problem of optimal placement of communications relay nodes. It is based on a spatial discretization with a subsequent reduction to a shortest path problem. The case of a restricted number of available UVs is also considered here. We introduce two label correcting algorithms which are able to take advantage of using some peculiarities of the resulting restricted shortest path problem. The algorithms produce a Pareto solution to the twoobjective problem of minimizing the path cost and the number of hops. We justify their correctness. The presented results of numerical 3D experiments show that our algorithms are superior to the conventional BellmanFord algorithm tailored to solving this problem. 
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2007  
[20] 
2007. A framework for reconfigurable path planning for autonomous unmanned aerial vehicles. Manuscript (preprint).

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2006  
[19] 
2006. Proceedings of the 10th International Conference on Principles of Knowledge Representation and Reasoning. Conference Proceedings.
AAAI Press. ISBN: 9781577352815. he National Conference on Artificial Intelligence remains the bellwether for research in artificial intelligence. Leading AI researchers and practitioners as well as scientists and engineers in related fields present theoretical, experimental, and empirical results, covering a broad range of topics that include principles of cognition, perception, and action; the design, application, and evaluation of AI algorithms and systems; architectures and frameworks for classes of AI systems; and analyses of tasks and domains in which intelligent systems perform. The Innovative Applications of Artificial Intelligence conference highlights successful applications of AI technology; explores issues, methods, and lessons learned in the development and deployment of AI applications; and promotes an interchange of ideas between basic and applied AI. This volume presents the proceedings of the latest conferences, held in July, 2006. 
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2003  
[18] 
2003. Knowledge Representation and Approximate Reasoning. Conference Proceedings.
In series: Fundamenta Informaticae #2003(57):24. IOS Press. Note: Special Issue 
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[17] 
2003. 1st International Workshop on Knowledge Representation and Approximate Reasoning (KR&AR). 
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1998  
[16] 
1998. Delayed effects of actions = direct effects + causal rules. Technical Report.
In series: Linköping Electronic Articles in Computer and Information Science #98001. Linköping University Electronic Press. Link: http://www.ep.liu.se/ea/cis/1998/001/ <strong></strong> We propose an approach to modeling delayed effects of actions which is based on the use of causal constraints and their interaction with the direct effects of actions. The approach extends previous work with a causal approach used to deal with the ramification problem. We show the similarity between solutions to the modeling of indirect effects and delayed effects of actions by example. The base logic PMON+ is a temporal logic for reasoning about action and change and uses circumscription. It is shown that the extension for delayed effects of actions retains the firstorder reducibility property shown previously for successfully dealing with the frame and ramification problems for a large class of action scenarios. We also consider the “causal qualification” problem, \"natural death\" of fluents and causal lag, each of which is closely related to the use of delayed effects. 
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1996  
[15] 
1996. PMON+: A fluent logic for action and change  formal specification, version 1.0. Technical Report.
In series: LITHIDAR #33. Department of Computer and Information Science, Linköping University. This report describes the current state of work with PMON, a logic for reasoning about action and change, and its extensions. PMON has been assessed correct for the KIA class using Sandewall's Features and Fluents framework which provides tools for assessing the correctness of logics of action and change. A syntactic characterization of PMON has previously been provided in terms of a circumscription axiom which is shown to be reducible to a firstorder formula. This report introduces a number of new extensions which are also reducible and deal with ramification. The report is intended to provide a formal specification for the PMON family of logics and the surface language L(SD) used to represent action scenario descriptions. It should be considered a working draft. The title of the report has a version number because both the languages and logics used are continually evolving. Since this document is intended as a formal specification which is used by our group as a reference for research and implementation, it is understandably brief as regards intuitions and applications of the languages and logics defined. We do provide a set of benchmarks and comments concerning these which can serve as a means of comparing this formalism with others. The set of benchmarks is not complete and is only intended to provide representative examples of the expressivity and use of this particular family of logics. We describe its features and limitations in other publications by our group which can normally be found at \"http://www.ida.liu.se/labs/kplab/\". 
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[14] 
1996. Declarative ptime queries to relational databases. Technical Report.
In series: LITHIDAR #34. Department of Computer and Information Science, Linköping University. 
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[13] 
1996. Preferential action semantics, preliminary report. Technical Report.
In series: LITHIDAR #??. Department of Computer and Information Science, Linköping University. In this paper, we propose a new way of considering reasoning about action and change. Rather than placing a preferential structure onto the models of logical theories, we place such a structure directly on the semantics of the actions involved. In this way, we obtain a preferential semantics of actions by means of which we can not only deal with several of the traditional problems in this area such as the frame and ramification problems, but can generalize these solutions to a context which includes both nondeterministic and concurrent actions. In fact, the net result is an integration of semantical and verificational techniques from the paradigm of imperative and concurrent programs in particular, as known from traditional programming, with the AI perspective. In this paper, the main focus is on semantical (i.e. model theoretical) issues rather than providing a logical calculus, which would be the next step in the endeavor. 
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[12] 
1996. General domain circumscription and its firstorder reduction. Technical Report.
In series: LITHIDAR #1. Department of Computer and Information Science, Linköping University. 
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1995  
[11] 
1995. A characterization result for circumscribed normal logic programs. Revised version accepted for publication: Special issue of honor of H. Rasiowa, Fundamenta Informaticae. Technical Report.
In series: LITHIDAR #20. Department of Computer and Information Science, Linköping University. 
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1994  
[10] 
1994. Computing circumscription revisited: A reduction algorithm. Technical Report.
In series: LITHIDAR #9442. Department of Computer and Information Science, Linköping University. In recent years, a great deal of attention has been devoted to logics of \"commonsense\" reasoning. Among the candidates proposed, circumscription has been perceived as an elegant mathematical technique for modeling nonmonotonic reasoning, but difficult to apply in practice. The major reason for this is the ndorder nature of circumscription axioms and the difficulty in finding proper substitutions of predicate expressions for predicate variables. One solution to this problem is to compile, where possible, ndorder formulas into equivalent 1storder formulas. Although some progress has been made using this approach, the results are not as strong as one might desire and they are isolated in nature. In this article, we provide a general method which can be used in an algorithmic manner to reduce circumscription axioms to 1storder formulas. The algorithm takes as input an arbitrary 2ndorder formula and either returns as output an equivalent 1storder formula, or terminates with failure. The class of 2ndorder formulas, and analogously the class of circumscriptive theories which can be reduced, provably subsumes those covered by existing results. We demonstrate the generality of the algorithm using circumscriptive theories with mixed quantifiers (some involving Skolemization), variable constants, nonseparated formulas, and formulas with nary predicate variables. In addition, we analyze the strength of the algorithm and compare it with existing approaches providing formal subsumption results. 
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[9] 
1994. Notes on PMON circumscription. Technical Report.
In series: LITHIDAR #43. Department of Computer and Information Science, Linköping University. 
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1992  
[8] 
1992. FONML3  A firstorder nonmonotonic logic with explicit defaults. Technical Report.
In series: LITHIDAR #20. Department of Computer and Information Science, Linköping University. 
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[7] 
1992. Fuzzy ifthenunless rules and their implementation. Technical Report.
In series: LITHIDAR #21. Department of Computer and Information Science, Linköping University. 
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[6] 
1992. Partiality, paraconsistency and preference modeling: Preliminary version. Technical Report.
In series: LITHIDAR #18. Department of Computer and Information Systems, Linköping University. 
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[5] 
1992. A constraintbased approach to proof procedures for multivalued logics. Technical Report.
In series: LITHIDAR #2. Department of Computer and Information Science, Linköping university, Linköping, Sweden. 
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1991  
[4] 
1991. NML3  A nonmonotonic logic with explicit defaults. Technical Report.
In series: Användarrapport #13. Department of Computer and Information Science, Linköping University. 
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1990  
[3] 
1990. NM3  A threevalued nonmonotonic formalism. Preliminary report. Technical Report.
In series: LITHIDAR #44. Department of Computer and Information Science, Linköping University. 
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[2] 
1990. A correspondence between inheritance hierarchies and a logic of preferential entailment. Technical Report.
In series: LITHIDAR #??. Department of Computer and Information Science, Linköping University. 
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1985  
[1] 
1985. A rule interpreter for an emycinlike expert system tool. Technical Report.
In series: Aslab Memo #8505. Linköpings tekniska högskola. 
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