A (7/2)-Approximation Algorithm for Guarding Orthogonal Art Galleries with Sliding Cameras

Consider a sliding camera that travels back and forth along an orthogonal line segment $s$ inside an orthogonal polygon $P$ with $n$ vertices. The camera can see a point $p$ inside $P$ if and only if there exists a line segment containing $p$ that crosses $s$ at a right angle and is completely contained in $P$. In the minimum sliding cameras (MSC) problem, the objective is to guard $P$ with the minimum number of sliding cameras. In this paper, we give an $O(n^{5/2})$-time $(7/2)$-approximation algorithm to the MSC problem on any simple orthogonal polygon with $n$ vertices, answering a question posed by Katz and Morgenstern (2011). To the best of our knowledge, this is the first constant-factor approximation algorithm for this problem.Comment: 11 page

Mobile vs. point guards

We study the problem of guarding orthogonal art galleries with horizontal mobile guards (alternatively, vertical) and point guards, using "rectangular vision". We prove a sharp bound on the minimum number of point guards required to cover the gallery in terms of the minimum number of vertical mobile guards and the minimum number of horizontal mobile guards required to cover the gallery. Furthermore, we show that the latter two numbers can be calculated in linear time.Comment: This version covers a previously missing case in both Phase 2 &

Task-driven multi-formation control for coordinated UAV/UGV ISR missions

The report describes the development of a theoretical framework for coordination and control of combined teams of UAVs and UGVs for coordinated ISR missions. We consider the mission as a composition of an ordered sequence of subtasks, each to be performed by a different team. We design continuous cooperative controllers that enable each team to perform a given subtask and we develop a discrete strategy for interleaving the action of teams on different subtasks. The overall multi-agent coordination architecture is captured by a hybrid automaton, stability is studied using Lyapunov tools, and performance is evaluated through numerical simulations

Formal methods for analysing, coordinating, and controlling decisions in multi-agent systems

Multiagentensysteme sind verteilte (Computer)Systeme, die sich aus autonomen interagierenden Systemkomponenten, bezeichnet als Agenten, zusammensetzen. Sie bieten ein flexibles Framework zur Modellierung und Analyse von interaktiven Systemen, in denen Kooperation, Eigeninteresse und Autonomie eine entscheidende Rolle spielen. Dies ist zum Beispiel der Fall in Smart Grids. Eine Herausforderung in solchen Systemen ist die Kontrolle und die Koordination von Systemausführungen. Agenten handeln autonom und lassen sich daher oftmals nicht direkt kontrollieren, sondern bestenfalls beeinflussen. Aufgrund der Autonomie und des Selbstinteresses, ist es schwierig, angemessene Kontrollmechanismen zu finden. Die vorliegende Arbeit behandelt formale Grundlagen zu den Themen Entscheidungsfindung, Koordination und Kontrolle in Multiagentensystemen. Insbesondere werden in diesem Zusammenhang Logiken zur Analyse und Spezifikation von strategischen Fähigkeiten von Agenten, unter diversen Restriktionen, untersucht. Es werden formale Ansätze zur Beeinflussung und Überwachung von Systemausführungen eingeführt. In einem weiteren Teil der Arbeit wird mittels spieltheoretischer Verfahren analysiert, wie rationale Agenten interagieren und Entscheidungen treffen. Es wird argumentiert, dass formale Methoden und Werkzeuge zur Analyse und Kontrolle von autonomen Systemen entscheidend für deren verlässliche Entwicklung sind.Multi-agent systems (MASs) are distributed (computer) systems composed of autonomously (inter-)acting system components referred to as agents. MASs offer a flexible framework to model and analyse many real world settings in which cooperation, self-interest, and autonomy are crucial elements. A key challenge in such settings is the control and coordination of behavior. However, due to the agents' autonomy behavior can often not be controlled, but at best be influenced in some way or another. For example, agents can be given incentives in order to affect their decision-making in such a way that the emergent behavior of all actors is desirable from the system's perspective. The properties of self-interest and autonomy make it challenging to find appropriate control mechanisms. Existing coordination and control approaches from the distributed system literature are often not applicable due to the lack of direct control on the system components of MASs. New methods and tools are needed. In this thesis formal foundations related to the subjects of decision making, coordination and control in MASs are studied. In particular, we investigate (extensions of) temporal and strategic logics which capture specific capabilities of agents that influence their decision making. We also propose formal approaches to control, coordinate and monitor the emergent behavior in MASs. In the last part of the thesis we analyse how rational agents interact and make decisions using game theoretical methods. We argue that such formal approaches and tools to analyse and control autonomous systems are crucial for the development of reliable and flexible systems and will become even more crucial in the near future

Network-Based Vertex Dissolution

We introduce a graph-theoretic vertex dissolution model that applies to a number of redistribution scenarios such as gerrymandering in political districting or work balancing in an online situation. The central aspect of our model is the deletion of certain vertices and the redistribution of their load to neighboring vertices in a completely balanced way. We investigate how the underlying graph structure, the knowledge of which vertices should be deleted, and the relation between old and new vertex loads influence the computational complexity of the underlying graph problems. Our results establish a clear borderline between tractable and intractable cases.Comment: Version accepted at SIAM Journal on Discrete Mathematic

Critical phenomena in complex networks

The combination of the compactness of networks, featuring small diameters, and their complex architectures results in a variety of critical effects dramatically different from those in cooperative systems on lattices. In the last few years, researchers have made important steps toward understanding the qualitatively new critical phenomena in complex networks. We review the results, concepts, and methods of this rapidly developing field. Here we mostly consider two closely related classes of these critical phenomena, namely structural phase transitions in the network architectures and transitions in cooperative models on networks as substrates. We also discuss systems where a network and interacting agents on it influence each other. We overview a wide range of critical phenomena in equilibrium and growing networks including the birth of the giant connected component, percolation, k-core percolation, phenomena near epidemic thresholds, condensation transitions, critical phenomena in spin models placed on networks, synchronization, and self-organized criticality effects in interacting systems on networks. We also discuss strong finite size effects in these systems and highlight open problems and perspectives.Comment: Review article, 79 pages, 43 figures, 1 table, 508 references, extende

Data catalog series for space science and applications flight missions. Volume 3A: Descriptions of low- and medium-altitude scientific spacecraft and investigations

Earth orbits spacecraft whose apogees are well below geostationary altitude and whose primary purpose is to conduct investigations in the near-Earth environment are considered

Partitioning Perfect Graphs into Stars

The partition of graphs into "nice" subgraphs is a central algorithmic problem with strong ties to matching theory. We study the partitioning of undirected graphs into same-size stars, a problem known to be NP-complete even for the case of stars on three vertices. We perform a thorough computational complexity study of the problem on subclasses of perfect graphs and identify several polynomial-time solvable cases, for example, on interval graphs and bipartite permutation graphs, and also NP-complete cases, for example, on grid graphs and chordal graphs.Comment: Manuscript accepted to Journal of Graph Theor

A CONTEXT-AWARE ROLE-PLAYING AUTOMATON FOR SELF-ADAPTIVE SYSTEMS

Role-based modeling and programming will become more and more important to realize big, complex, and adaptive software systems [Zhu and Alkins, 2006]. Therefore, the Object-Oriented Programming (OOP) paradigm is extended with roles, where objects can begin to play roles and drop roles dynamically at runtime. Playing a role is changing the object’s type which can add or change behavior. Roles are a dynamic view of the state and behavior of objects at runtime at a point of time highlighting their relations to other objects. Self-adaptive systems (SAS) are naturally context-aware systems. Thus, adaption is always seen in a context e.g., because a sensor value passes a specified limit, or because the reason could be derived from the knowledge about the past and presence. However, there is currently no common concept describing the situation (e.g., the context or other conditions that lead to a specific adaption) in which objects begin to play and stop playing roles. Current role programming languages therefore suffer from the problem of tangling of different aspects i.e., the context logic, the role adaption logic, and the business logic. This leads to less understandable and unmaintainable code [Antinyan et al., 2014]. Thomas Kühn has drafted in his major thesis [Kühn, 2011] a behavioral model to describe role binding with storyboards. This allows to model concisely role reconfigurations, but the concept lacks the ability to specify context-dependent behavior which is crucial for self-adaptive systems, and is built on top of an outdated understanding of the role concept which lacks compartments. The concept of storyboards will be extended with the ability to address context-dependent conditions. Compartments will be added in order to adapt the current wider understanding of the concept of roles. This will result in a concept for context-aware storyboards with roles which provide a separation of concerns approach w.r.t. the above named concerns. The concept will be implemented as automaton and will be evaluated on a use case. The use case is a robotic co-working scenario based on the idea of [Haddadin et al., 2009].:1. Introduction 1.1. Motivation 1.2. Outline 2. Background and Concepts 2.1. Role-Based Design 2.1.1. Roles and Role Models 2.1.2. Role Binding 2.1.3. Role Runtime Systems 2.2. Modeling Concepts for a Role-Playing Automaton 2.2.1. Models and Meta-models 2.2.2. Behavioral Diagrams and Automata 2.2.3. Storyboards 2.3. Relevant Software Architectures 2.3.1. Context-Aware Computing 2.3.2. Self-Adaptive Systems 2.3.3. Event-Based Systems 2.4. Summary 3. Requirements Analysis 3.1. Problem Analysis 3.2. Goals and Requirements 3.3. Technology Analysis and Selection 3.3.1. Pattern Matching 3.3.2. Model Execution 3.4. Summary 4. Concept for a Role-Playing Automaton for Self-Adaptive Systems 4.1. Context-Aware Storyboards with Roles 4.2. Syntax and Semantics 4.2.1. Overview 4.2.2. Story Pattern 4.2.3. Transitions, Events, and Guards 4.2.4. Control Nodes 4.2.5. Variable Binding 4.3. Meta-Model 4.4. Differences to Related Concepts 4.4.1. Relation to UML Activity Diagrams 4.4.2. Differences to Story Diagrams 4.4.3. Differences to Storyboards with Roles 4.5. Summary 5. Implementation 5.1. Architecture 5.2. Implementation 5.2.1. Grammar and Meta-model 5.2.2. Model Transformation 5.2.3. Graph Transformation 5.2.4. The Role Model 5.2.5. Context and Events 5.2.6. Model Execution and Validation 5.3. Summary 6. Related Work 6.1. Context-Aware Middleware for URC System 6.2. Context Petri Nets 6.3. Agent-Based and Context-Oriented Approach for Web Services Composition 6.4. Model Driven Design of Service-Based Context-Aware Applications 6.5. Summary 7. Evaluation 7.1. Use Case Robotic Co-Worker 7.2.Results 7.3.Summary 8. Conclusion and FutureWork 8.1.Conclusion 8.2.FutureWork A. Appendices A.1. Grammar for Storyboards with Roles A.2. Exemplary of a StoryDiagram A.3. Meta-Model of Context-Aware Storyboards With Role