TY - GEN AU - Schaefer, Johannes Sebastian ID - 689 TI - Routing Algorithms on Delayed Networks for Disaster Management Support ER - TY - GEN AB - In this paper, we solve the local gathering problem of a swarm of $n$ indistinguishable, point-shaped robots on a two dimensional grid in asymptotically optimal time $\mathcal{O}(n)$ in the fully synchronous $\mathcal{FSYNC}$ time model. Given an arbitrarily distributed (yet connected) swarm of robots, the gathering problem on the grid is to locate all robots within a $2\times 2$-sized area that is not known beforehand. Two robots are connected if they are vertical or horizontal neighbors on the grid. The locality constraint means that no global control, no compass, no global communication and only local vision is available; hence, a robot can only see its grid neighbors up to a constant $L_1$-distance, which also limits its movements. A robot can move to one of its eight neighboring grid cells and if two or more robots move to the same location they are \emph{merged} to be only one robot. The locality constraint is the significant challenging issue here, since robot movements must not harm the (only globally checkable) swarm connectivity. For solving the gathering problem, we provide a synchronous algorithm -- executed by every robot -- which ensures that robots merge without breaking the swarm connectivity. In our model, robots can obtain a special state, which marks such a robot to be performing specific connectivity preserving movements in order to allow later merge operations of the swarm. Compared to the grid, for gathering in the Euclidean plane for the same robot and time model the best known upper bound is $\mathcal{O}(n^2)$. AU - Cord-Landwehr, Andreas AU - Fischer, Matthias AU - Jung, Daniel AU - Meyer auf der Heide, Friedhelm ID - 16450 T2 - arXiv:1602.03303 TI - Asymptotically Optimal Gathering on a Grid ER - TY - CONF AB - We apply methods of genetic programming to a general problem from software engineering, namely example-based generation of specifications. In particular, we focus on model transformation by example. The definition and implementation of model transformations is a task frequently carried out by domain experts, hence, a (semi-)automatic approach is desirable. This application is challenging because the underlying search space has rich semantics, is high-dimensional, and unstructured. Hence, a computationally brute-force approach would be unscalable and potentially infeasible. To address that problem, we develop a sophisticated approach of designing complex mutation operators. We define ‘patterns’ for constructing mutation operators and report a successful case study. Furthermore, the code of the evolved model transformation is required to have high maintainability and extensibility, that is, the code should be easily readable by domain experts. We report an evaluation of this approach in a software engineering case study. AU - Kühne, Thomas AU - Hamann, Heiko AU - Arifulina, Svetlana AU - Engels, Gregor ID - 169 T2 - Proceedings of the 19th European Conference on Genetic Programming (EuroGP 2016) TI - Patterns for Constructing Mutation Operators: Limiting the Search Space in a Software Engineering Application ER - TY - GEN AU - Handirk, Tobias ID - 1082 TI - Über die Rolle von Informationen in Verkehrsnetzwerken ER - TY - THES AU - Cord-Landwehr, Andreas ID - 154 SN - 978-3-942647-72-4 TI - Selfish Network Creation - On Variants of Network Creation Games VL - 353 ER - TY - CONF AB - Consider a scheduling problem in which a set of jobs with interjob communication, canonically represented by a weighted tree, needs to be scheduled on m parallel processors interconnected by a shared communication channel. In each time step, we may allow any processed job to use a certain capacity of the channel in order to satisfy (parts of) its communication demands to adjacent jobs processed in parallel. The goal is to find a schedule that minimizes the makespan and in which communication demands of all jobs are satisfied.We show that this problem is NP-hard in the strong sense even if the number of processors and the maximum degree of the underlying tree is constant.Consequently, we design and analyze simple approximation algorithms with asymptotic approximation ratio 2-2/m in case of paths and a ratio of 5/2 in case of arbitrary trees. AU - König, Jürgen AU - Mäcker, Alexander AU - Meyer auf der Heide, Friedhelm AU - Riechers, Sören ID - 157 T2 - Proceedings of the 10th Annual International Conference on Combinatorial Optimization and Applications (COCOA) TI - Scheduling with Interjob Communication on Parallel Processors ER - TY - JOUR AB - Abstract—Max-min fairness (MMF) is a widely known approachto a fair allocation of bandwidth to each of the usersin a network. This allocation can be computed by uniformlyraising the bandwidths of all users without violating capacityconstraints. We consider an extension of these allocations byraising the bandwidth with arbitrary and not necessarily uniformtime-depending velocities (allocation rates). These allocationsare used in a game-theoretic context for routing choices, whichwe formalize in progressive filling games (PFGs). We present avariety of results for equilibria in PFGs. We show that these gamespossess pure Nash and strong equilibria. While computation ingeneral is NP-hard, there are polynomial-time algorithms forprominent classes of Max-Min-Fair Games (MMFG), includingthe case when all users have the same source-destination pair.We characterize prices of anarchy and stability for pure Nashand strong equilibria in PFGs and MMFGs when players havedifferent or the same source-destination pairs. In addition, weshow that when a designer can adjust allocation rates, it is possibleto design games with optimal strong equilibria. Some initial resultson polynomial-time algorithms in this direction are also derived. AU - Harks, Tobias AU - Höfer, Martin AU - Schewior, Kevin AU - Skopalik, Alexander ID - 159 IS - 4 JF - IEEE/ACM Transactions on Networking TI - Routing Games With Progressive Filling ER - TY - CONF AB - In this paper we consider a strategic variant of the online facility location problem. Given is a graph in which each node serves two roles: it is a strategic client stating requests as well as a potential location for a facility. In each time step one client states a request which induces private costs equal to the distance to the closest facility. Before serving, the clients may collectively decide to open new facilities, sharing the corresponding price. Instead of optimizing the global costs, each client acts selfishly. The prices of new facilities vary between nodes and also change over time, but are always bounded by some fixed value α. Both the requests as well as the facility prices are given by an online sequence and are not known in advance.We characterize the optimal strategies of the clients and analyze their overall performance in comparison to a centralized offline solution. If all players optimize their own competitiveness, the global performance of the system is O(√α⋅α) times worse than the offline optimum. A restriction to a natural subclass of strategies improves this result to O(α). We also show that for fixed facility costs, we can find strategies such that this bound further improves to O(√α). AU - Drees, Maximilian AU - Feldkord, Björn AU - Skopalik, Alexander ID - 149 T2 - Proceedings of the 10th Annual International Conference on Combinatorial Optimization and Applications (COCOA) TI - Strategic Online Facility Location ER - TY - GEN ED - Dressler, Falko ED - Meyer auf der Heide, Friedhelm ID - 163 TI - Proceedings of the 17th ACM International Symposium on Mobile Ad Hoc Networking and Computing (MobiHoc) ER - TY - CONF AB - Defining, measuring, and comparing the quality and efficiency of rendering algorithms in computer graphics is a demanding challenge: quality measures are often application specific and efficiency is strongly influenced by properties of the rendered scene and the used hardware. We survey the currently employed evaluation methods for AQ1 the development process of rendering algorithms. Then, we present our PADrend framework, which supports systematic and flexible development, evaluation, adaptation, and comparison of rendering algorithms, and provides a comfortable and easy-to-use platform for developers of rendering algorithms. The system includes a new evaluation method to improve the objectivity of experimental evaluations of rendering algorithms. AU - Fischer, Matthias AU - Jähn, Claudius AU - Meyer auf der Heide, Friedhelm AU - Petring, Ralf ED - Kliemann, Lasse ED - Sanders, Peter ID - 16351 T2 - Algorithm Engineering TI - Algorithm Engineering Aspects of Real-Time Rendering Algorithms VL - 9220 ER - TY - CONF AU - Li, Shouwei AU - Meyer auf der Heide, Friedhelm AU - Podlipyan, Pavel ID - 16358 T2 - Algorithms for Sensor Systems, Proceedings of the 12th International Symposium on Algorithms and Experiments for Wireless Sensor Networks (ALGOSENSORS) TI - The impact of the Gabriel subgraph of the visibility graph on the gathering of mobile autonomous robots ER - TY - CONF AB - In this paper, we solve the local gathering problem of a swarm of n indistinguishable, point-shaped robots on a two dimensional grid in asymptotically optimal time O(n) in the fully synchronous FSYNC time model. Given an arbitrarily distributed (yet connected) swarm of robots, the gathering problem on the grid is to locate all robots within a 2x2- sized area that is not known beforehand. Two robots are connected if they are vertical or horizontal neighbors on the grid. The locality constraint means that no global control, no compass, no global communication and only local vision is available; hence, a robot can only see its grid neighbors up to a constant L1-distance, which also limits its movements. A robot can move to one of its eight neighboring grid cells and if two or more robots move to the same location they are merged to be only one robot. The locality constraint is the significant challenging issue here, since robot move- ments must not harm the (only globally checkable) swarm connectivity. For solving the gathering problem, we provide a synchronous algorithm { executed by every robot { which ensures that robots merge without breaking the swarm con- nectivity. In our model, robots can obtain a special state, which marks such a robot to be performing specific connec- tivity preserving movements in order to allow later merge operations of the swarm. Compared to the grid, for gath- ering in the Euclidean plane for the same robot and time model the best known upper bound is O(n^2). AU - Cord-Landwehr, Andreas AU - Fischer, Matthias AU - Jung, Daniel AU - Meyer auf der Heide, Friedhelm ID - 16359 T2 - Proceedings of the 28th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA) TI - Asymptotically Optimal Gathering on a Grid ER - TY - CONF AB - We consider the following variant of the two dimensional gathering problem for swarms of robots: Given a swarm of n indistinguishable, point shaped robots on a two dimensional grid. Initially, the robots form a closed chain on the grid and must keep this connectivity during the whole process of their gathering. Connectivity means, that neighboring robots of the chain need to be positioned at the same or neighboring points of the grid. In our model, gathering means to keep shortening the chain until the robots are located inside a 2*2 subgrid. Our model is completely local (no global control, no global coordinates, no compass, no global communication or vision, ...). Each robot can only see its next constant number of left and right neighbors on the chain. This fixed constant is called the viewing path length. All its operations and detections are restricted to this constant number of robots. Other robots, even if located at neighboring or the same grid point cannot be detected. Only based on the relative positions of its detectable chain neighbors, a robot can decide to obtain a certain state. Based on this state and their local knowledge, the robots do local modifications to the chain by moving to neighboring grid points without breaking the chain. These modifications are performed without the knowledge whether they lead to a global progress or not. We assume the fully synchronous FSYNC model. For this problem, we present a gathering algorithm which needs linear time. This result generalizes a result, where an open chain with specified distinguishable (and fixed) endpoints is considered. AU - Abshoff, Sebastian AU - Cord-Landwehr, Andreas AU - Fischer, Matthias AU - Jung, Daniel AU - Meyer auf der Heide, Friedhelm ID - 16360 T2 - Proceedings of the 30th International Parallel and Distributed Processing Symposium (IPDPS) TI - Gathering a Closed Chain of Robots on a Grid ER - TY - CONF AU - Macker, Alexander AU - Malatyali, Manuel AU - Meyer auf der Heide, Friedhelm ID - 16364 SN - 9781509021406 T2 - 2016 IEEE International Parallel and Distributed Processing Symposium (IPDPS) TI - On Competitive Algorithms for Approximations of Top-k-Position Monitoring of Distributed Streams ER - TY - GEN AB - We consider a scheduling problem where machines need to be rented from the cloud in order to process jobs. There are two types of machines available which can be rented for machine-type dependent prices and for arbitrary durations. However, a machine-type dependent setup time is required before a machine is available for processing. Jobs arrive online over time, have machine-type dependent sizes and have individual deadlines. The objective is to rent machines and schedule jobs so as to meet all deadlines while minimizing the rental cost. Since we observe the slack of jobs to have a fundamental influence on the competitiveness, we study the model when instances are parameterized by their (minimum) slack. An instance is called to have a slack of $\beta$ if, for all jobs, the difference between the job's release time and the latest point in time at which it needs to be started is at least $\beta$. While for $\beta < s$ no finite competitiveness is possible, our main result is an $O(\frac{c}{\varepsilon} + \frac{1}{\varepsilon^3})$-competitive online algorithm for $\beta = (1+\varepsilon)s$ with $\frac{1}{s} \leq \varepsilon \leq 1$, where $s$ and $c$ denotes the largest setup time and the cost ratio of the machine-types, respectively. It is complemented by a lower bound of $\Omega(\frac{c}{\varepsilon})$. AU - Mäcker, Alexander AU - Malatyali, Manuel AU - Meyer auf der Heide, Friedhelm AU - Riechers, Sören ID - 16396 T2 - arXiv:1609.01184 TI - Cost-efficient Scheduling on Machines from the Cloud ER - TY - JOUR AB - We consider online optimization problems in which certain goods have to be acquired in order to provide a service or infrastructure. Classically, decisions for such problems are considered as final: one buys the goods. However, in many real world applications, there is a shift away from the idea of buying goods. Instead, leasing is often a more flexible and lucrative business model. Research has realized this shift and recently initiated the theoretical study of leasing models (Anthony and Gupta in Proceedings of the integer programming and combinatorial optimization: 12th International IPCO Conference, Ithaca, NY, USA, June 25–27, 2007; Meyerson in Proceedings of the 46th Annual IEEE Symposium on Foundations of Computer Science (FOCS 2005), 23–25 Oct 2005, Pittsburgh, PA, USA, 2005; Nagarajan and Williamson in Discret Optim 10(4):361–370, 2013) We extend this line of work and suggest a more systematic study of leasing aspects for a class of online optimization problems. We provide two major technical results. We introduce the leasing variant of online set multicover and give an O(log(mK)logn)-competitive algorithm (with n, m, and K being the number of elements, sets, and leases, respectively). Our results also imply improvements for the non-leasing variant of online set cover. Moreover, we extend results for the leasing variant of online facility location. Nagarajan and Williamson (Discret Optim 10(4):361–370, 2013) gave an O(Klogn)-competitive algorithm for this problem (with n and K being the number of clients and leases, respectively). We remove the dependency on n (and, thereby, on time). In general, this leads to a bound of O(lmaxloglmax) (with the maximal lease length lmax). For many natural problem instances, the bound improves to O(K2). AU - Abshoff, Sebastian AU - Kling, Peter AU - Markarian, Christine AU - Meyer auf der Heide, Friedhelm AU - Pietrzyk, Peter ID - 139 IS - 4 JF - Journal of Combinatorial Optimization TI - Towards the price of leasing online ER - TY - CONF AB - We present an efficient parallel algorithm for the general Monotone Circuit Value Problem (MCVP) with n gates and an underlying graph of bounded genus k. Our algorithm generalizes a recent result by Limaye et al. who showed that MCVP with toroidal embedding (genus 1) is in NC when the input contains a toroidal embedding of the circuit. In addition to extending this result from genus 1 to any bounded genus k, and unlike the work reported by Limaye et al., we do not require a precomputed embedding to be given. Most importantly, our results imply that given a P-complete problem, it is possible to find an algorithm that makes the problem fall into NC by fixing one or more parameters. Hence, we deduce the interesting analogy: Fixed Parameter Parallelizable (FPP) is with respect to P-complete what Fixed Parameter Tractable (FPT) is with respect to NP-complete. Similar work that uses treewidth as parameter was also presented by Elberfeld et al. in [6]. AU - Abu-Khzam, Faisal N. AU - Li, Shouwei AU - Markarian, Christine AU - Meyer auf der Heide, Friedhelm AU - Podlipyan, Pavel ID - 143 T2 - Proceedings of the 22nd International Conference on Computing and Combinatorics (COCOON) TI - The Monotone Circuit Value Problem with Bounded Genus Is in NC ER - TY - JOUR AB - Comparative evaluations of peer-to-peer protocols through simulations are a viable approach to judge the performance and costs of the individual protocols in large-scale networks. In order to support this work, we present the peer-to-peer system simulator PeerfactSim.KOM, which we extended over the last years. PeerfactSim.KOM comes with an extensive layer model to support various facets and protocols of peer-to-peer networking. In this article, we describe PeerfactSim.KOM and show how it can be used for detailed measurements of large-scale peer-to-peer networks. We enhanced PeerfactSim.KOM with a fine-grained analyzer concept, with exhaustive automated measurements and gnuplot generators as well as a coordination control to evaluate sets of experiment setups in parallel. Thus, by configuring all experiments and protocols only once and starting the simulator, all desired measurements are performed, analyzed, evaluated, and combined, resulting in a holistic environment for the comparative evaluation of peer-to-peer systems. An immediate comparison of different configurations and overlays under different aspects is possible directly after the execution without any manual post-processing. AU - Feldotto, Matthias AU - Graffi, Kalman ID - 145 IS - 5 JF - Concurrency and Computation: Practice and Experience TI - Systematic evaluation of peer-to-peer systems using PeerfactSim.KOM VL - 28 ER - TY - GEN AU - Pfannschmidt, Karlson ID - 251 TI - Solving the aggregated bandits problem ER - TY - CONF AU - Wahby, Mostafa AU - Hamann, Heiko ID - 19959 T2 - Applications of Evolutionary Computation (EvoApplications 2015) TI - On the Tradeoff between Hardware Protection and Optimization Success: A Case Study in Onboard Evolutionary Robotics for Autonomous Parallel Parking ER - TY - CONF AB - Besides the life-as-it-could-be driver of artificial life research there is also the concept of extending natural life by creating hybrids or mixed societies that are built from natural and artificial components. In this paper we motivate and present the research program of the project flora robotica. Our objective is to develop and to investigate closely linked symbiotic relationships between robots and natural plants and to explore the potentials of a plant-robot society able to produce architectural artifacts and living spaces. These robot-plant bio-hybrids create synergies that allow for new functions of plants and robots. They also create novel design opportunities for an architecture that fuses the design and construction phase. The bio-hybrid is an example of mixed societies between 'hard' artificial and 'wet' natural life, which enables an interaction between natural and artificial ecologies. They form an embodied, self-organizing, and distributed cognitive system which is supposed to grow and develop over long periods of time resulting in the creation of meaningful architectural structures. A key idea is to assign equal roles to robots and plants in order to create a highly integrated, symbiotic system. Besides the gain of knowledge, this project has the objective to create a bio-hybrid system with a defined function and application -- growing architectural artifacts. AU - Hamann, Heiko AU - Wahby, Mostafa AU - Schmickl, Thomas AU - Zahadat, Payam AU - Hofstadler, Daniel AU - Stoy, Kasper AU - Risi, Sebastian AU - Faina, Andres AU - Veenstra, Frank AU - Kernbach, Serge AU - Kuksin, Igor AU - Kernbach, Olga AU - Ayres, Phil AU - Wojtaszek, Przemyslaw ID - 19960 SN - 9781479975600 T2 - Proceedings of the 2015 IEEE Symposium on Artificial Life (IEEE ALIFE'15) TI - Flora Robotica - Mixed Societies of Symbiotic Robot-Plant Bio-Hybrids ER - TY - JOUR AB - Recent approaches in evolutionary robotics (ER) propose to generate behavioral diversity in order to evolve desired behaviors more easily. These approaches require the definition of a behavioral distance, which often includes task-specific features and hence a priori knowledge. Alternative methods, which do not explicitly force selective pressure towards diversity (SPTD) but still generate it, are known from the field of artificial life, such as in artificial ecologies (AEs). In this study, we investigate how SPTD is generated without task-specific behavioral features or other forms of a priori knowledge and detect how methods of generating SPTD can be transferred from the domain of AE to ER. A promising finding is that in both types of systems, in systems from ER that generate behavioral diversity and also in the investigated speciation model, selective pressure is generated towards unpopulated regions of search space. In a simple case study we investigate the practical implications of these findings and point to options for transferring the idea of self-organizing SPTD in AEs to the domain of ER. AU - Hamann, Heiko ID - 19962 JF - Artificial Life SN - 1064-5462 TI - Lessons from Speciation Dynamics: How to Generate Selective Pressure Towards Diversity ER - TY - CONF AB - Aggregation is a crucial task in swarm robotics to ensure cooperation. We investigate the task of aggregation on an area specified indirectly by certain environmental features, here it is a light distribution. We extend the original BEECLUST algorithm, that implements an aggregation behavior, to an adaptive variant that automatically adapts to any light conditions. We compare these two control algorithms in a number of swarm robot experiments with different light conditions. The improved, adaptive variant is found to be significantly better in the tested setup. AU - Wahby, Mostafa AU - Weinhold, Alexander AU - Hamann, Heiko ID - 19966 SN - 9781631901003 T2 - Proceedings of the 9th EAI International Conference on Bio-inspired Information and Communications Technologies (formerly BIONETICS) TI - Revisiting BEECLUST: Aggregation of Swarm Robots with Adaptiveness to Different Light Settings ER - TY - CONF AU - Wahby, Mostafa AU - Divband Soorati, Mohammad AU - von Mammen, Sebastian AU - Hamann, Heiko ID - 19967 T2 - Proceedings. 25. Computational Intelligence Workshop TI - Evolution of Controllers for Robot-Plant Bio-Hybdrids: A Simple Case Study Using a Model of Plant Growth and Motion ER - TY - CONF AB - Fitness function design is known to be a critical feature of the evolutionary-robotics approach. Potentially, the complexity of evolving a successful controller for a given task can be reduced by integrating a priori knowledge into the fitness function which complicates the comparability of studies in evolutionary robotics. Still, there are only few publications that study the actual effects of different fitness functions on the robot's performance. In this paper, we follow the fitness function classification of Nelson et al. (2009) and investigate a selection of four classes of fitness functions that require different degrees of a priori knowledge. The robot controllers are evolved in simulation using NEAT and we investigate different tasks including obstacle avoidance and (periodic) goal homing. The best evolved controllers were then post-evaluated by examining their potential for adaptation, determining their convergence rates, and using cross-comparisons based on the different fitness function classes. The results confirm that the integration of more a priori knowledge can simplify a task and show that more attention should be paid to fitness function classes when comparing different studies. AU - Hamann, Heiko AU - Divband Soorati, Mohammad ID - 19980 T2 - Proceedings of the Genetic and Evolutionary Computation Conference (GECCO 2015) TI - The Effect of Fitness Function Design on Performance in Evolutionary Robotics: The Influence of a Priori Knowledge ER - TY - CONF AU - Hamann, Heiko AU - Schmickl, Thomas AU - Zahadat, Payam ID - 19988 T2 - 13th European Conference on Artificial Life (ECAL 2015) TI - Evolving Collective Behaviors With Diverse But Predictable Sensor States ER - TY - CHAP AU - Hamann, Heiko AU - Correll, Nikolaus AU - Kacprzyk, Janusz AU - Pedrycz, Witold ID - 19989 T2 - Springer Handbook of Computational Intelligence TI - Probabilistic Modeling of Swarming Systems ER - TY - CONF AU - Ding, Hongli AU - Hamann, Heiko ID - 19990 T2 - First International Symposium on Swarm Behavior and Bio-Inspired Robotics (SWARM 2015) TI - Dependability in Swarm Robotics: Error Detection and Correction ER - TY - CONF AU - Hamann, Heiko AU - Schmickl, Thomas AU - Kengyel, Daniela AU - Zahadat, Payam AU - Radspieler, Gerald AU - Wotawa, Franz ID - 19991 T2 - Principles and Practice of Multi-Agent Systems (PRIMA 2015) TI - Potential of Heterogeneity in Collective Behaviors: A Case Study on Heterogeneous Swarms ER - TY - JOUR AU - Valentini, Gabriele AU - Hamann, Heiko ID - 19992 JF - Swarm Intelligence SN - 1935-3812 TI - Time-variant feedback processes in collective decision-making systems: influence and effect of dynamic neighborhood sizes ER - TY - CONF AU - Dorigo, Marco AU - Hamann, Heiko AU - Valentini, Gabriele ID - 20005 T2 - Proceedings of the 14th Int. Conf. on Autonomous Agents and Multiagent Systems (AAMAS 2015) TI - Efficient Decision-Making in a Self-Organizing Robot Swarm: On the Speed Versus Accuracy Trade-Off ER - TY - CONF AU - Dorigo, Marco AU - Hamann, Heiko AU - Valentini, Gabriele ID - 20006 T2 - AAAI-15 Video Proceedings TI - Self-organized collective decisions in a robot swarm ER - TY - CONF AB - Many markets have seen a shift from the idea of buying and moved to leasing instead. Arguably, the latter has been the major catalyst for their success. Ten years ago, research realized this shift and initiated the study of "online leasing problems" by introducing leasing to online optimization problems. Resources required to provide a service in an "online leasing problem" are no more bought but leased for different durations. In this paper, we provide an overview of results that contribute to the understanding of "online resource leasing problems". AU - Markarian, Christine AU - Meyer auf der Heide, Friedhelm ID - 266 T2 - Proceedings of the 2015 ACM Symposium on Principles of Distributed Computing (PODC) TI - Online Resource Leasing ER - TY - THES AU - Markarian, Christine ID - 267 TI - Online Resource Leasing ER - TY - JOUR AB - We consider structural and algorithmic questions related to the Nash dynamics of weighted congestion games. In weighted congestion games with linear latency functions, the existence of pure Nash equilibria is guaranteed by a potential function argument. Unfortunately, this proof of existence is inefficient and computing pure Nash equilibria in such games is a PLS-hard problem even when all players have unit weights. The situation gets worse when superlinear (e.g., quadratic) latency functions come into play; in this case, the Nash dynamics of the game may contain cycles and pure Nash equilibria may not even exist. Given these obstacles, we consider approximate pure Nash equilibria as alternative solution concepts. A ρ--approximate pure Nash equilibrium is a state of a (weighted congestion) game from which no player has any incentive to deviate in order to improve her cost by a multiplicative factor higher than ρ. Do such equilibria exist for small values of ρ? And if so, can we compute them efficiently?We provide positive answers to both questions for weighted congestion games with polynomial latency functions by exploiting an “approximation” of such games by a new class of potential games that we call Ψ-games. This allows us to show that these games have d!-approximate pure Nash equilibria, where d is the maximum degree of the latency functions. Our main technical contribution is an efficient algorithm for computing O(1)-approximate pure Nash equilibria when d is a constant. For games with linear latency functions, the approximation guarantee is 3+√5/2 + Oγ for arbitrarily small γ > 0; for latency functions with maximum degree d≥ 2, it is d2d+o(d). The running time is polynomial in the number of bits in the representation of the game and 1/γ. As a byproduct of our techniques, we also show the following interesting structural statement for weighted congestion games with polynomial latency functions of maximum degree d ≥ 2: polynomially-long sequences of best-response moves from any initial state to a dO(d2)-approximate pure Nash equilibrium exist and can be efficiently identified in such games as long as d is a constant.To the best of our knowledge, these are the first positive algorithmic results for approximate pure Nash equilibria in weighted congestion games. Our techniques significantly extend our recent work on unweighted congestion games through the use of Ψ-games. The concept of approximating nonpotential games by potential ones is interesting in itself and might have further applications. AU - Caragiannis, Ioannis AU - Fanelli, Angelo AU - Gravin, Nick AU - Skopalik, Alexander ID - 320 IS - 1 JF - Transactions on Economics and Computation TI - Approximate Pure Nash Equilibria in Weighted Congestion Games: Existence, Efficient Computation, and Structure VL - 3 ER - TY - GEN AU - Pautz, Jannis ID - 316 TI - Budget Games with priced strategies ER - TY - THES AU - Jähn, Claudius ID - 317 TI - Bewertung von Renderingalgorithmen für komplexe 3-D-Szenen ER - TY - THES AU - Abshoff, Sebastian ID - 270 TI - On the Complexity of Fundamental Problems in Dynamic Ad-hoc Networks ER - TY - CONF AB - In \emph{bandwidth allocation games} (BAGs), the strategy of a player consists of various demands on different resources. The player's utility is at most the sum of these demands, provided they are fully satisfied. Every resource has a limited capacity and if it is exceeded by the total demand, it has to be split between the players. Since these games generally do not have pure Nash equilibria, we consider approximate pure Nash equilibria, in which no player can improve her utility by more than some fixed factor $\alpha$ through unilateral strategy changes. There is a threshold $\alpha_\delta$ (where $\delta$ is a parameter that limits the demand of each player on a specific resource) such that $\alpha$-approximate pure Nash equilibria always exist for $\alpha \geq \alpha_\delta$, but not for $\alpha < \alpha_\delta$. We give both upper and lower bounds on this threshold $\alpha_\delta$ and show that the corresponding decision problem is ${\sf NP}$-hard. We also show that the $\alpha$-approximate price of anarchy for BAGs is $\alpha+1$. For a restricted version of the game, where demands of players only differ slightly from each other (e.g. symmetric games), we show that approximate Nash equilibria can be reached (and thus also be computed) in polynomial time using the best-response dynamic. Finally, we show that a broader class of utility-maximization games (which includes BAGs) converges quickly towards states whose social welfare is close to the optimum. AU - Drees, Maximilian AU - Feldotto, Matthias AU - Riechers, Sören AU - Skopalik, Alexander ID - 271 T2 - Proceedings of the 8th International Symposium on Algorithmic Game Theory (SAGT) TI - On Existence and Properties of Approximate Pure Nash Equilibria in Bandwidth Allocation Games ER - TY - CONF AB - Consider the problem in which n jobs that are classified into k types are to be scheduled on m identical machines without preemption. A machine requires a proper setup taking s time units before processing jobs of a given type. The objective is to minimize the makespan of the resulting schedule. We design and analyze an approximation algorithm that runs in time polynomial in n,m and k and computes a solution with an approximation factor that can be made arbitrarily close to 3/2. AU - Mäcker, Alexander AU - Malatyali, Manuel AU - Meyer auf der Heide, Friedhelm AU - Riechers, Sören ED - Dehne, Frank ED - Sack, Jörg Rüdiger ED - Stege, Ulrike ID - 274 T2 - Algorithms and Data Structures: 14th International Symposium, WADS 2015, Victoria, BC, Canada, August 5-7, 2015. Proceedings TI - Non-preemptive Scheduling on Machines with Setup Times ER - TY - CONF AB - We investigate a non-cooperative game-theoretic model for the formation of communication networks by selfish agents. Each agent aims for a central position at minimum cost for creating edges. In particular, the general model (Fabrikant et al., PODC'03) became popular for studying the structure of the Internet or social networks. Despite its significance, locality in this game was first studied only recently (Bilò et al., SPAA'14), where a worst case locality model was presented, which came with a high efficiency loss in terms of quality of equilibria. Our main contribution is a new and more optimistic view on locality: agents are limited in their knowledge and actions to their local view ranges, but can probe different strategies and finally choose the best. We study the influence of our locality notion on the hardness of computing best responses, convergence to equilibria, and quality of equilibria. Moreover, we compare the strength of local versus non-local strategy changes. Our results address the gap between the original model and the worst case locality variant. On the bright side, our efficiency results are in line with observations from the original model, yet we have a non-constant lower bound on the Price of Anarchy. AU - Cord-Landwehr, Andreas AU - Lenzner, Pascal ID - 275 T2 - Proceedings of the 40th Conference on Mathematical Foundations of Computer Science (MFCS) TI - Network Creation Games: Think Global - Act Local ER - TY - GEN AU - Kothe, Nils ID - 277 TI - Multilevel Netzwerk Spiele mit konstanten Entfernungen im Highspeed-Netzwerk ER - TY - CONF AU - Berssenbrügge, Jan AU - Wiederkehr, Olga AU - Jähn, Claudius AU - Fischer, Matthias ID - 17425 T2 - 12. Paderborner Workshop Augmented & Virtual Reality in der Produktentstehung TI - Anbindung des Virtuellen Prototypen an die Partialmodelle intelligenter technischer Systeme VL - 343 ER - TY - CONF AU - Jähn, Claudius AU - Fischer, Matthias AU - Gerges, Maria AU - Berssenbrügge, Jan ID - 17427 T2 - 12. Paderborner Workshop Augmented & Virtual Reality in der Produktentstehung TI - Automatische Ableitung geometrischer Eigenschaften von Bauteilen aus dem 3-D-Polygonmodell VL - 342 ER - TY - BOOK ED - Gausemeier, Jürgen ED - Grafe, Michael ED - Meyer auf der Heide, Friedhelm ID - 17431 TI - Augmented & Virtual Reality in der Produktentstehung: Grundlagen, Methoden und Werkzeuge; Interaktions- und Visualisierungstechniken, Virtual Prototyping intelligenter technischer Systeme mit AR/VR VL - 342 ER - TY - JOUR AB - Inter-datacenter transfers of non-interactive but timely large flows over a private (managed) network is an important problem faced by many cloud service providers. The considered flows are non-interactive because they do not explicitly target the end users. However, most of them must be performed on a timely basis and are associated with a deadline. We propose to schedule these flows by a centralized controller, which determines when to transmit each flow and which path to use. Two scheduling models are presented in this paper. In the first, the controller also determines the rate of each flow, while in the second bandwidth is assigned by the network according to the TCP rules. We develop scheduling algorithms for both models and compare their complexity and performance. AU - Cohen, R. AU - Polevoy, Gleb ID - 17657 IS - 99 JF - Cloud Computing, IEEE Transactions on KW - Approximation algorithms KW - Approximation methods KW - Bandwidth KW - Cloud computing KW - Routing KW - Schedules KW - Scheduling SN - 2168-7161 TI - Inter-Datacenter Scheduling of Large Data Flows VL - PP ER - TY - JOUR AB - Abstract We study the problem of bandwidth allocation with multiple interferences. In this problem the input consists of a set of users and a set of base stations. Each user has a list of requests, each consisting of a base station, a frequency demand, and a profit that may be gained by scheduling this request. The goal is to find a maximum profit set of user requests S that satisfies the following conditions: (i) S contains at most one request per user, (ii) the frequency sets allotted to requests in S that correspond to the same base station are pairwise non-intersecting, and (iii) the QoS received by any user at any frequency is reasonable according to an interference model. In this paper we consider two variants of bandwidth allocation with multiple interferences. In the first each request specifies a demand that can be satisfied by any subset of frequencies that is large enough. In the second each request specifies a specific frequency interval. Furthermore, we consider two interference models, multiplicative and additive. We show that these problems are extremely hard to approximate if the interferences depend on both the interfered and the interfering base stations. On the other hand, we provide constant factor approximation algorithms for both variants of bandwidth allocation with multiple interferences for the case where the interferences depend only on the interfering base stations. We also consider a restrictive special case that is closely related to the Knapsack problem. We show that this special case is NP-hard and that it admits an FPTAS. AU - Bar-Yehuda, Reuven AU - Polevoy, Gleb AU - Rawitz, Dror ID - 17658 JF - Discrete Applied Mathematics KW - Local ratio SN - 0166-218X TI - Bandwidth allocation in cellular networks with multiple interferences VL - 194 ER - TY - CONF AB - We consider online leasing problems in which demands arrive over time and need to be served by leasing resources. We introduce a new model for these problems such that a resource can be leased for K different durations each incurring a different cost (longer leases cost less per time unit). Each demand i can be served anytime between its arrival ai and its deadline ai+di by a leased resource. The objective is to meet all deadlines while minimizing the total leasing costs. This model is a natural generalization of Meyerson’s ParkingPermitProblem (FOCS 2005) in which di=0 for all i. We propose an online algorithm that is Θ(K+dmaxlmin)-competitive where dmax and lmin denote the largest di and the shortest available lease length, respectively. We also extend the SetCoverLeasing problem by deadlines and give a competitive online algorithm which also improves on existing solutions for the original SetCoverLeasing problem. AU - Li, Shouwei AU - Mäcker, Alexander AU - Markarian, Christine AU - Meyer auf der Heide, Friedhelm AU - Riechers, Sören ID - 240 T2 - Proceedings of the 21st Annual International Computing and Combinatorics Conference (COCOON) TI - Towards Flexible Demands in Online Leasing Problems ER - TY - GEN AB - We consider the following variant of the two dimensional gathering problem for swarms of robots: Given a swarm of $n$ indistinguishable, point shaped robots on a two dimensional grid. Initially, the robots form a closed chain on the grid and must keep this connectivity during the whole process of their gathering. Connectivity means, that neighboring robots of the chain need to be positioned at the same or neighboring points of the grid. In our model, gathering means to keep shortening the chain until the robots are located inside a $2\times 2$ subgrid. Our model is completely local (no global control, no global coordinates, no compass, no global communication or vision, \ldots). Each robot can only see its next constant number of left and right neighbors on the chain. This fixed constant is called the \emph{viewing path length}. All its operations and detections are restricted to this constant number of robots. Other robots, even if located at neighboring or the same grid point cannot be detected. Only based on the relative positions of its detectable chain neighbors, a robot can decide to obtain a certain state. Based on this state and their local knowledge, the robots do local modifications to the chain by moving to neighboring grid points without breaking the chain. These modifications are performed without the knowledge whether they lead to a global progress or not. We assume the fully synchronous $\mathcal{FSYNC}$ model. For this problem, we present a gathering algorithm which needs linear time. This result generalizes the result from \cite{hopper}, where an open chain with specified distinguishable (and fixed) endpoints is considered. AU - Abshoff, Sebastian AU - Cord-Landwehr, Andreas AU - Fischer, Matthias AU - Jung, Daniel AU - Meyer auf der Heide, Friedhelm ID - 16449 T2 - arXiv:1510.05454 TI - Gathering a Closed Chain of Robots on a Grid ER - TY - GEN AB - We consider the problem of dominating set-based virtual backbone used for routing in asymmetric wireless ad-hoc networks. These networks have non-uniform transmission ranges and are modeled using the well-established disk graphs. The corresponding graph theoretic problem seeks a strongly connected dominating-absorbent set of minimum cardinality in a digraph. A subset of nodes in a digraph is a strongly connected dominating-absorbent set if the subgraph induced by these nodes is strongly connected and each node in the graph is either in the set or has both an in-neighbor and an out-neighbor in it. Distributed algorithms for this problem are of practical significance due to the dynamic nature of ad-hoc networks. We present a first distributed approximation algorithm, with a constant approximation factor and O(Diam) running time, where Diam is the diameter of the graph. Moreover we present a simple heuristic algorithm and conduct an extensive simulation study showing that our heuristic outperforms previously known approaches for the problem. AU - Abu-Khzam, Faisal N. AU - Markarian, Christine AU - Meyer auf der Heide, Friedhelm AU - Schubert, Michael ID - 16452 T2 - arXiv:1510.01866 TI - Approximation and Heuristic Algorithms for Computing Backbones in Asymmetric Ad-Hoc Networks ER -