TY - CONF
AB - Many 3D scenes (e.g. generated from CAD data) are composed of a multitude of objects that are nested in each other. A showroom, for instance, may contain multiple cars and every car has a gearbox with many gearwheels located inside. Because the objects occlude each other, only few are visible from outside. We present a new technique, Spherical Visibility Sampling (SVS), for real-time 3D rendering of such -- possibly highly complex -- scenes. SVS exploits the occlusion and annotates hierarchically structured objects with directional visibility information in a preprocessing step. For different directions, the directional visibility encodes which objects of a scene's region are visible from the outside of the regions' enclosing bounding sphere. Since there is no need to store a separate view space subdivision as in most techniques based on preprocessed visibility, a small memory footprint is achieved. Using the directional visibility information for an interactive walkthrough, the potentially visible objects can be retrieved very efficiently without the need for further visibility tests. Our evaluation shows that using SVS allows to preprocess complex 3D scenes fast and to visualize them in real time (e.g. a Power Plant model and five animated Boeing 777 models with billions of triangles). Because SVS does not require hardware support for occlusion culling during rendering, it is even applicable for rendering large scenes on mobile devices.
AU - Eikel, Benjamin
AU - Jähn, Claudius
AU - Fischer, Matthias
AU - Meyer auf der Heide, Friedhelm
ID - 16393
IS - 4
SN - 0167-7055
T2 - Computer Graphics Forum
TI - Spherical Visibility Sampling
VL - 32
ER -
TY - CHAP
AB - In order to evaluate the efficiency of algorithms for real-time 3D rendering, different properties like rendering time, occluded triangles, or image quality, need to be investigated. Since these properties depend on the position of the camera, usually some camera path is chosen, along which the measurements are performed. As those measurements cover only a small part of the scene, this approach hardly allows drawing conclusions regarding the algorithm's properties at arbitrary positions in the scene. The presented method allows the systematic and position-independent evaluation of rendering algorithms. It uses an adaptive sampling approach to approximate the distribution of a property (like rendering time) for all positions in the scene. This approximation can be visualized to produce an intuitive impression of the algorithm's behavior or be statistically analyzed for objectively rating and comparing algorithms. We demonstrate our method by evaluating performance aspects of a known occlusion culling algorithm.
AU - Jähn, Claudius
AU - Eikel, Benjamin
AU - Fischer, Matthias
AU - Petring, Ralf
AU - Meyer auf der Heide, Friedhelm
ID - 16406
SN - 0302-9743
T2 - Advances in Visual Computing
TI - Evaluation of Rendering Algorithms Using Position-Dependent Scene Properties
ER -
TY - CONF
AB - We study two-party communication in the context of directed dynamic networks that are controlled by an adaptive adversary. This adversary is able to change all edges as long as the networks stay strongly-connected in each round. In this work, we establish a relation between counting the total number of nodes in the network and the problem of exchanging tokens between two communication partners which communicate through a dynamic network. We show that the communication problem for a constant fraction of n tokens in a dynamic network with n nodes is at most as hard as counting the number of nodes in a dynamic network with at most 4n+3 nodes. For the proof, we construct a family of directed dynamic networks and apply a lower bound from two-party communication complexity.
AU - Abshoff, Sebastian
AU - Benter, Markus
AU - Malatyali, Manuel
AU - Meyer auf der Heide, Friedhelm
ID - 507
T2 - Proceedings of the 17th International Conference on Principles of Distributed Systems (OPODIS)
TI - On Two-Party Communication Through Dynamic Networks
ER -
TY - THES
AB - Diese Arbeit besch{\"a}ftigt sich mit dem Facility Location Problem. Dies ist ein Optimierungsproblem, bei dem festgelegt werden muss an welchen Positionen Ressourcen zur Verf{\"u}gung gestellt werden, so dass diese von Nutzern gut erreicht werden k{\"o}nnen. Es sollen dabei Kosten minimiert werden, die zum einen durch Bereitstellung von Ressourcen und zum anderen durch Verbindungskosten zwischen Nutzern und Ressourcen entstehen. Die Schwierigkeit des Problems liegt darin, dass man einerseits m{\"o}glichst wenige Ressourcen zur Verf{\"u}gung stellen m{\"o}chte, andererseits daf{\"u}r sorgen muss, dass sich Nutzer nicht all zu weit weg von Ressourcen befinden. Dies w{\"u}rde n{\"a}mlich hohe Verbindungskosten nach sich ziehen. Das Facility Location Problem wurde bereits sehr intensiv in vielen unterschiedlichen Varianten untersucht. In dieser Arbeit werden drei Varianten des Problems modelliert und neue Algorithmen f{\"u}r sie entwickelt und bez{\"u}glich ihres Approximationsfaktors und ihrer Laufzeit analysiert. Jede dieser drei untersuchten Varianten hat einen besonderen Schwerpunkt. Bei der ersten Varianten handelt es sich um ein Online Problem, da hier die Eingabe nicht von Anfang an bekannt ist, sondern Schritt f{\"u}r Schritt enth{\"u}llt wird. Die Schwierigkeit hierbei besteht darin unwiderrufliche Entscheidungen treffen zu m{\"u}ssen ohne dabei die Zukunft zu kennen und trotzdem eine zu jeder Zeit gute L{\"o}sung angeben zu k{\"o}nnen. Der Schwerpunkt der zweiten Variante liegt auf Lokalit{\"a}t, die z.B. in Sensornetzwerken von großer Bedeutung ist. Hier soll eine L{\"o}sung verteilt und nur mit Hilfe von lokalen Information berechnet werden. Schließlich besch{\"a}ftigt sich die dritte Variante mit einer verteilten Berechnung, bei welcher nur eine stark beschr{\"a}nkte Datenmenge verschickt werden darf und dabei trotzdem ein sehr guter Approximationsfaktor erreicht werden muss. Die bei der Analyse der Approximationsfaktoren bzw. der Kompetitivit{\"a}t verwendeten Techniken basieren zum großen Teil auf Absch{\"a}tzung der primalen L{\"o}sung mit Hilfe einer L{\"o}sung des zugeh{\"o}rigen dualen Problems. F{\"u}r die Modellierung von Lokalit{\"a}t wird das weitverbreitete LOCAL Modell verwendet. In diesem Modell werden f{\"u}r die Algorithmen subpolynomielle obere Laufzeitschranken gezeigt.
AU - Pietrzyk, Peter
ID - 514
TI - Local and Online Algorithms for Facility Location
ER -
TY - CONF
AB - We present a new online algorithm for profit-oriented scheduling on multiple speed-scalable processors.Moreover, we provide a tight analysis of the algorithm's competitiveness.Our results generalize and improve upon work by \citet{Chan:2010}, which considers a single speed-scalable processor.Using significantly different techniques, we can not only extend their model to multiprocessors but also prove an enhanced and tight competitive ratio for our algorithm.In our scheduling problem, jobs arrive over time and are preemptable.They have different workloads, values, and deadlines.The scheduler may decide not to finish a job but instead to suffer a loss equaling the job's value.However, to process a job's workload until its deadline the scheduler must invest a certain amount of energy.The cost of a schedule is the sum of lost values and invested energy.In order to finish a job the scheduler has to determine which processors to use and set their speeds accordingly.A processor's energy consumption is power $\Power{s}$ integrated over time, where $\Power{s}=s^{\alpha}$ is the power consumption when running at speed $s$.Since we consider the online variant of the problem, the scheduler has no knowledge about future jobs.This problem was introduced by~\citet{Chan:2010} for the case of a single processor.They presented an online algorithm which is $\alpha^{\alpha}+2e\alpha$-competitive.We provide an online algorithm for the case of multiple processors with an improved competitive ratio of $\alpha^{\alpha}$.
AU - Kling, Peter
AU - Pietrzyk, Peter
ID - 499
T2 - Proceedings of the 25th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA)
TI - Profitable Scheduling on Multiple Speed-Scalable Processors
ER -
TY - GEN
ED - Gausemeier, Jürgen
ED - Grafe, Michael
ED - Meyer auf der Heide, Friedhelm
ID - 17443
TI - 11. Paderborner Workshop Augmented & Virtual Reality in der Produktentstehung
VL - 311
ER -
TY - CHAP
AB - Many virtual 3D scenes, especially those that are large, are not structured evenly. For such heterogeneous data, there is no single algorithm that is able to render every scene type at each position fast and with the same high image quality. For a small set of scenes, this situation can be improved if different rendering algorithms are manually assigned to particular parts of the scene by an experienced user. We introduce the Multi-Algorithm-Rendering method. It automatically deploys different rendering algorithms simultaneously for a broad range of scene types. The method divides the scene into subregions and measures the behavior of different algorithms for each region in a preprocessing step. During runtime, this data is utilized to compute an estimate for the quality and running time of the available rendering algorithms from the observer's point of view. By solving an optimizing problem, the image quality can be optimized by an assignment of algorithms to regions while keeping the frame rate almost constant.
AU - Petring, Ralf
AU - Eikel, Benjamin
AU - Jähn, Claudius
AU - Fischer, Matthias
AU - Meyer auf der Heide, Friedhelm
ID - 16407
SN - 0302-9743
T2 - Advances in Visual Computing
TI - Real-Time 3D Rendering of Heterogeneous Scenes
ER -
TY - GEN
ED - Flocchini, Paola
ED - Gao, Jie
ED - Kranakis, Evangelos
ED - Meyer auf der Heide, Friedhelm
ID - 558
TI - Algorithms for Sensor Systems - 9th International Symposium on Algorithms and Experiments for Sensor Systems, Wireless Networks and Distributed Robotics
VL - 8243
ER -
TY - CONF
AB - We present and study a new model for energy-aware and profit-oriented scheduling on a single processor.The processor features dynamic speed scaling as well as suspension to a sleep mode.Jobs arrive over time, are preemptable, and have different sizes, values, and deadlines.On the arrival of a new job, the scheduler may either accept or reject the job.Accepted jobs need a certain energy investment to be finished in time, while rejected jobs cause costs equal to their values.Here, power consumption at speed $s$ is given by $P(s)=s^{\alpha}+\beta$ and the energy investment is power integrated over time.Additionally, the scheduler may decide to suspend the processor to a sleep mode in which no energy is consumed, though awaking entails fixed transition costs $\gamma$.The objective is to minimize the total value of rejected jobs plus the total energy.Our model combines aspects from advanced energy conservation techniques (namely speed scaling and sleep states) and profit-oriented scheduling models.We show that \emph{rejection-oblivious} schedulers (whose rejection decisions are not based on former decisions) have – in contrast to the model without sleep states – an unbounded competitive ratio.It turns out that the jobs' value densities (the ratio between a job's value and its work) are crucial for the performance of such schedulers.We give an algorithm whose competitiveness nearly matches the lower bound w.r.t\text{.} the maximum value density.If the maximum value density is not too large, the competitiveness becomes $\alpha^{\alpha}+2e\alpha$.Also, we show that it suffices to restrict the value density of low-value jobs only.Using a technique from \cite{Chan:2010} we transfer our results to processors with a fixed maximum speed.
AU - Cord-Landwehr, Andreas
AU - Kling, Peter
AU - Mallmann Trenn, Fredrik
ED - Even, Guy
ED - Rawitz, Dror
ID - 580
T2 - Proceedings of the 1st Mediterranean Conference on Algorithms (MedAlg)
TI - Slow Down & Sleep for Profit in Online Deadline Scheduling
ER -
TY - CONF
AB - We consider an online facility location problem where clients arrive over time and their demands have to be served by opening facilities and assigning the clients to opened facilities. When opening a facility we must choose one of K different lease types to use. A lease type k has a certain lease length lk. Opening a facility i using lease type k causes a cost of f k i and ensures that i is open for the next lk time steps. In addition to costs for opening facilities, we have to take connection costs ci j into account when assigning a client j to facility i. We develop and analyze the first online algorithm for this problem that has a time-independent competitive factor.This variant of the online facility location problem was introduced by Nagarajan and Williamson [7] and is strongly related to both the online facility problem by Meyerson [5] and the parking permit problem by Meyerson [6]. Nagarajan and Williamson gave a 3-approximation algorithm for the offline problem and an O(Klogn)-competitive algorithm for the online variant. Here, n denotes the total number of clients arriving over time. We extend their result by removing the dependency on n (and thereby on the time). In general, our algorithm is O(lmax log(lmax))-competitive. Here lmax denotes the maximum lease length. Moreover, we prove that it is O(log2(lmax))-competitive for many “natural” cases. Such cases include, for example, situations where the number of clients arriving in each time step does not vary too much, or is non-increasing, or is polynomially bounded in lmax.
AU - Meyer auf der Heide, Friedhelm
AU - Pietrzyk, Peter
AU - Kling, Peter
ID - 636
T2 - Proceedings of the 19th International Colloquium on Structural Information & Communication Complexity (SIROCCO)
TI - An Algorithm for Facility Leasing
ER -
TY - JOUR
AB - A left-to-right maximum in a sequence of n numbers s_1, …, s_n is a number that is strictly larger than all preceding numbers. In this article we present a smoothed analysis of the number of left-to-right maxima in the presence of additive random noise. We show that for every sequence of n numbers s_i ∈ [0,1] that are perturbed by uniform noise from the interval [-ε,ε], the expected number of left-to-right maxima is Θ(&sqrt;n/ε + log n) for ε>1/n. For Gaussian noise with standard deviation σ we obtain a bound of O((log3/2 n)/σ + log n).We apply our results to the analysis of the smoothed height of binary search trees and the smoothed number of comparisons in the quicksort algorithm and prove bounds of Θ(&sqrt;n/ε + log n) and Θ(n/ε+1&sqrt;n/ε + n log n), respectively, for uniform random noise from the interval [-ε,ε]. Our results can also be applied to bound the smoothed number of points on a convex hull of points in the two-dimensional plane and to smoothed motion complexity, a concept we describe in this article. We bound how often one needs to update a data structure storing the smallest axis-aligned box enclosing a set of points moving in d-dimensional space.
AU - Damerow, Valentina
AU - Manthey, Bodo
AU - Meyer auf der Heide, Friedhelm
AU - Räcke, Harald
AU - Scheideler, Christian
AU - Sohler, Christian
AU - Tantau, Till
ID - 579
IS - 3
JF - Transactions on Algorithms
TI - Smoothed analysis of left-to-right maxima with applications
ER -
TY - THES
AB - Wir betrachten eine Gruppe von mobilen, autonomen Robotern in einem ebenen Gel{\"a}nde. Es gibt keine zentrale Steuerung und die Roboter m{\"u}ssen sich selbst koordinieren. Zentrale Herausforderung dabei ist, dass jeder Roboter nur seine unmittelbare Nachbarschaft sieht und auch nur mit Robotern in seiner unmittelbaren Nachbarschaft kommunizieren kann. Daraus ergeben sich viele algorithmische Fragestellungen. In dieser Arbeit wird untersucht, unter welchen Voraussetzungen die Roboter sich auf einem Punkt versammeln bzw. eine Linie zwischen zwei festen Stationen bilden k{\"o}nnen. Daf{\"u}r werden mehrere Roboter-Strategien in verschiedenen Bewegungsmodellen vorgestellt. Diese Strategien werden auf ihre Effizienz hin untersucht. Es werden obere und untere Schranken f{\"u}r die ben{\"o}tigte Anzahl Runden und die Bewegungsdistanz gezeigt. In einigen F{\"a}llen wird außerdem die ben{\"o}tigte Bewegungsdistanz mit derjenigen Bewegungsdistanz verglichen, die eine optimale globale Strategie auf der gleichen Instanz ben{\"o}tigen w{\"u}rde. So werden kompetititve Faktoren hergeleitet.
AU - Kempkes, Barbara
ID - 601
TI - Local strategies for robot formation problems
ER -
TY - CHAP
AU - Kempkes, Barbara
AU - Meyer auf der Heide, Friedhelm
ID - 16448
SN - 0302-9743
T2 - Algorithms for Sensor Systems
TI - Local, Self-organizing Strategies for Robotic Formation Problems
ER -
TY - CONF
AB - Dynamics in networks is caused by a variety of reasons, like nodes moving in 2D (or 3D) in multihop cellphone networks, joins and leaves in peer-to-peer networks, evolution in social networks, and many others. In order to understand such kinds of dynamics, and to design distributed algorithms that behave well under dynamics, many ways to model dynamics are introduced and analyzed w.r.t. correctness and eciency of distributed algorithms. In [16], Kuhn, Lynch, and Oshman have introduced a very general, worst case type model of dynamics: The edge set of the network may change arbitrarily from step to step, the only restriction is that it is connected at all times and the set of nodes does not change. An extended model demands that a xed connected subnetwork is maintained over each time interval of length T (T-interval dynamics). They have presented, among others, algorithms for counting the number of nodes under such general models of dynamics.In this paper, we generalize their models and algorithms by adding random edge faults, i.e., we consider fault-prone dynamic networks: We assume that an edge currently existing may fail to transmit data with some probability p. We rst observe that strong counting, i.e., each node knows the correct count and stops, is not possible in a model with random edge faults. Our main two positive results are feasibility and runtime bounds for weak counting, i.e., stopping is no longer required (but still a correct count in each node), and for strong counting with an upper bound, i.e., an upper bound N on n is known to all nodes.
AU - Brandes, Philipp
AU - Meyer auf der Heide, Friedhelm
ID - 619
T2 - Proceedings of the 4th Workshop on Theoretical Aspects of Dynamic Distributed Systems (TADDS)
TI - Distributed Computing in Fault-Prone Dynamic Networks
ER -
TY - GEN
AU - Eidens, Fabian
ID - 638
TI - Adaptive Verbindungsstrategien in dynamischen Suchnetzwerken
ER -
TY - CHAP
AU - Kempkes, Barbara
AU - Meyer auf der Heide, Friedhelm
ID - 16445
SN - 0302-9743
T2 - Experimental Algorithms
TI - Continuous Local Strategies for Robotic Formation Problems
ER -
TY - CONF
AU - Kempkes, Barbara
AU - Kling, Peter
AU - Meyer auf der Heide, Friedhelm
ID - 16446
SN - 9781450312134
T2 - Proceedinbgs of the 24th ACM symposium on Parallelism in algorithms and architectures - SPAA '12
TI - Optimal and competitive runtime bounds for continuous, local gathering of mobile robots
ER -
TY - CONF
AB - Network creation games model the creation and usage costs of networks formed by a set of selfish peers.Each peer has the ability to change the network in a limited way, e.g., by creating or deleting incident links.In doing so, a peer can reduce its individual communication cost.Typically, these costs are modeled by the maximum or average distance in the network.We introduce a generalized version of the basic network creation game (BNCG).In the BNCG (by Alon et al., SPAA 2010), each peer may replace one of its incident links by a link to an arbitrary peer.This is done in a selfish way in order to minimize either the maximum or average distance to all other peers.That is, each peer works towards a network structure that allows himself to communicate efficiently with all other peers.However, participants of large networks are seldom interested in all peers.Rather, they want to communicate efficiently with a small subset only.Our model incorporates these (communication) interests explicitly.Given peers with interests and a communication network forming a tree, we prove several results on the structure and quality of equilibria in our model.We focus on the MAX-version, i.e., each node tries to minimize the maximum distance to nodes it is interested in, and give an upper bound of O(\sqrt(n)) for the private costs in an equilibrium of n peers.Moreover, we give an equilibrium for a circular interest graph where a node has private cost Omega(\sqrt(n)), showing that our bound is tight.This example can be extended such that we get a tight bound of Theta(\sqrt(n)) for the price of anarchy.For the case of general networks we show the price of anarchy to be Theta(n).Additionally, we prove an interesting connection between a maximum independent set in the interest graph and the private costs of the peers.
AU - Cord-Landwehr, Andreas
AU - Huellmann (married name: Eikel), Martina
AU - Kling, Peter
AU - Setzer, Alexander
ID - 628
T2 - Proceedings of the 5th International Symposium on Algorithmic Game Theory (SAGT)
TI - Basic Network Creation Games with Communication Interests
ER -
TY - CONF
AB - We present a parallel rendering system for heterogeneous PC clusters to visualize massive models. One single, powerful visualization node is supported by a group of backend nodes with weak graphics performance. While the visualization node renders the visible objects, the backend nodes asynchronously perform visibility tests and supply the front end with visible scene objects. The visualization node stores only currently visible objects in its memory, while the scene is distributed among the backend nodes’ memory without redundancy. To efficiently compute the occlusion tests in spite of that each backend node stores only a fraction of the original geometry, we complete the scene by adding highly simplified versions of the objects stored on other nodes. We test our system with 15 backend nodes. It is able to render a ≈ 350,M polygons (≈ 8.5,GiB) large aircraft model with 20, to 30,fps and thus allows a walk-through in real-time.
AU - Süß, Tim
AU - Koch, Clemens
AU - Jähn, Claudius
AU - Fischer, Matthias
AU - Meyer auf der Heide, Friedhelm
ID - 16408
SN - 0302-9743
T2 - Advances in Visual Computing
TI - Asynchronous Occlusion Culling on Heterogeneous PC Clusters for Distributed 3D Scenes
VL - 7431
ER -
TY - CONF
AU - Rajaraman, Rajmohan
AU - Meyer auf der Heide, Friedhelm
ID - 16428
SN - 9781450307437
TI - Proceedings of the 23rd ACM symposium on Parallelism in algorithms and architectures - SPAA '11
ER -
TY - CONF
AU - Kling, Peter
AU - Meyer auf der Heide, Friedhelm
ID - 16454
SN - 9781450307437
T2 - Proceedings of the 23rd ACM symposium on Parallelism in algorithms and architectures - SPAA '11
TI - Convergence of local communication chain strategies via linear transformations
ER -
TY - CHAP
AU - Brandes, Philipp
AU - Degener, Bastian
AU - Kempkes, Barbara
AU - Meyer auf der Heide, Friedhelm
ID - 16459
SN - 0302-9743
T2 - Structural Information and Communication Complexity
TI - Energy-Efficient Strategies for Building Short Chains of Mobile Robots Locally
ER -
TY - GEN
ED - Meyer auf der Heide, Friedhelm
ED - Rajaraman, Rajmohan
ID - 667
TI - 23rd Annual ACM Symposium on Parallelism in Algorithms and Architectures
ER -
TY - CONF
AU - Klaas, Alexander
AU - Laroque, Christoph
AU - Dangelmaier, Wilhelm
AU - Fischer, Matthias
ID - 17421
SN - 9781457721090
T2 - Proceedings of the 2011 Winter Simulation Conference (WSC)
TI - Simulation aided, knowledge based routing for AGVs in a distribution warehouse
ER -
TY - JOUR
AU - Degener, Bastian
AU - Fekete, Sándor P.
AU - Kempkes, Barbara
AU - Meyer auf der Heide, Friedhelm
ID - 16447
JF - Computer Science Review
SN - 1574-0137
TI - A survey on relay placement with runtime and approximation guarantees
ER -
TY - CHAP
AB - Given a set of n mobile robots in the d-dimensional Euclidean space, the goal is to let them converge to a single not predefined point. The challenge is that the robots are limited in their capabilities. Robots can, upon activation, compute the positions of all other robots using an individual affine coordinate system. The robots are indistinguishable, oblivious and may have different affine coordinate systems. A very general discrete time model assumes that robots are activated in arbitrary order. Further, the computation of a new target point may happen much earlier than the movement, so that the movement is based on outdated information about other robot's positions. Time is measured as the number of rounds, where a round ends as soon as each robot has moved at least once. In [Cohen, Peleg: Convergence properties of gravitational algorithms in asynchronous robot systems], the Center of Gravity is considered as target function, convergence was proven, and the number of rounds needed for halving the diameter of the convex hull of the robot's positions was shown to be O(n^2) and Omega(n). We present an easy-to-check property of target functions that guarantee convergence and yields upper time bounds. This property intuitively says that when a robot computes a new target point, this point is significantly within the current axes aligned minimal box containing all robots. This property holds, e.g., for the above-mentioned target function, and improves the above O(n^2) to an asymptotically optimal O(n) upper bound. Our technique also yields a constant time bound for a target function that requires all robots having identical coordinate axes.
AU - Cord-Landwehr, Andreas
AU - Degener, Bastian
AU - Fischer, Matthias
AU - Hüllmann, Martina
AU - Kempkes, Barbara
AU - Klaas, Alexander
AU - Kling, Peter
AU - Kurras, Sven
AU - Märtens, Marcus
AU - Meyer auf der Heide, Friedhelm
AU - Raupach, Christoph
AU - Swierkot, Kamil
AU - Warner, Daniel
AU - Weddemann, Christoph
AU - Wonisch, Daniel
ID - 16409
SN - 0302-9743
T2 - Automata, Languages and Programming
TI - A New Approach for Analyzing Convergence Algorithms for Mobile Robots
ER -
TY - CONF
AU - Vöcking, Berthold
AU - Hoefer, Martin
AU - Skopalik, Alexander
AU - Penn, Michal
AU - Polukarov, Maria
ID - 18568
T2 - {IJCAI} 2011, Proceedings of the 22nd International Joint Conference on Artificial Intelligence,
TI - Considerate Equilibrium
ER -
TY - JOUR
AU - Degener, Bastian
AU - Kempkes, Barbara
AU - Meyer auf der Heide, Friedhelm
ID - 16455
JF - Procedia Computer Science
SN - 1877-0509
TI - Building Simple Formations in Large Societies of Tiny Mobile Robots
ER -
TY - GEN
AU - Swierkot, Kamil
ID - 663
TI - Complexity Classes for Local Computation
ER -
TY - JOUR
AU - Hsu, D. Frank
AU - Magga, Bruce M.
AU - Ho, Howard C. T.
AU - Hromkovic, Juraj
AU - Lau, Francis C. M.
AU - Meyer auf der Heide, Friedhelm
ID - 17009
JF - Journal of Interconnection Networks
SN - 0219-2659
TI - EDITORIAL
ER -
TY - CHAP
AU - Gehweiler, Joachim
AU - Meyer auf der Heide, Friedhelm
ID - 16412
SN - 9783642153273
T2 - Algorithms Unplugged
TI - Bin Packing - How Do I Get My Stuff into the Boxes
ER -
TY - CHAP
AU - Degener, Bastian
AU - Kempkes, Barbara
AU - Meyer auf der Heide, Friedhelm
ID - 16456
SN - 9783034801294
T2 - Organic Computing — A Paradigm Shift for Complex Systems
TI - Energy-Awareness in Self-organising Robotic Exploration Teams
ER -
TY - CONF
AB - We present two distributed, constant factor approximation algorithms for the metric facility location problem. Both algorithms have been designed with a strong emphasis on applicability in the area of wireless sensor networks: in order to execute them, each sensor node only requires limited local knowledge and simple computations. Also, the algorithms can cope with measurement errors and take into account that communication costs between sensor nodes do not necessarily increase linearly with the distance, but can be represented by a polynomial. Since it cannot always be expected that sensor nodes execute algorithms in a synchronized way, our algorithms are executed in an asynchronous model (but they are still able to break symmetry that might occur when two neighboring nodes act at exactly the same time). Furthermore, they can deal with dynamic scenarios: if a node moves, the solution is updated and the update affects only nodes in the local neighborhood. Finally, the algorithms are robust in the sense that incorrect behavior of some nodes during some round will, in the end, still result in a good approximation. The first algorithm runs in expected O(log_{1+\epsilon} n) communication rounds and yields a \my^4(1+4\my^2(1+\epsilon)^{1/p})^p approximation, while the second has a running time of expected O(log^2_{1+\epsilon} n) communication rounds and an approximation factor of \my^4(1 + 2(1 + \epsilon)^{1/p})^p. Here, \epsilon > 0 is an arbitrarily small constant, p the exponent of the polynomial representing the communication costs, and \my the relative measurement error.
AU - Abshoff, Sebastan
AU - Cord-Landwehr, Andreas
AU - Degener, Bastian
AU - Kempkes, Barbara
AU - Pietrzyk, Peter
ID - 657
T2 - Proceedings of the 7th International Symposium on Algorithms for Sensor Systems, Wireless Ad Hoc Networks and Autonomous Mobile Entities (ALGOSENSORS)
TI - Local Approximation Algorithms for the Uncapacitated Metric Facility Location Problem in Power-Aware Sensor Networks
ER -
TY - CONF
AB - Web Computing is a variant of parallel computing where the idle times of PCs donated by worldwide distributed users are employed to execute parallel programs. The PUB-Web library developed by us supports this kind of usage of computing resources. A major problem for the efficient execution of such parallel programs is load balancing. In the Web Computing context, this problem becomes more difficult because of the dynamic behavior of the underlying "parallel computer": the set of available processors (donated PCs) as well as their availability (idle times) change over time in an unpredictable fashion.In this paper, we experimentally evaluate and compare load balancing algorithms in this scenario, namely a variant of the well-established Work Stealing algorithm and strategies based on a heterogeneous version of distributed hash-tables (DHHTs) introduced recently. In order to run a meaningful experimental evaluation, we employ, in addition to our Web Computing library PUB-Web, realistic data sets for the job input streams and for the dynamics of the availability of the resources.Our experimental evaluations suggest that Work Stealing is the better strategy if the number of processes ready to run matches the number of available processors. But a suitable variant of DHHTs outperforms Work Stealing if there are significantly more processes ready to run than available processors.
AU - Gehweiler, Joachim
AU - Kling, Peter
AU - Meyer auf der Heide, Friedhelm
ID - 664
T2 - Proceedings of the 9th International Conference on Parallel Processing and Applied Mathematics (PPAM)
TI - An Experimental Comparison of Load Balancing Strategies in a Web Computing Environment
ER -
TY - THES
AB - Web computing is a variant of parallel computing where the idle times of PCs
donated by worldwide distributed users are employed to execute parallel
programs. In this thesis we consider a web computing variant with two
important properties: First, we support the execution of coupled, massively
parallel algorithms (rather than distributed data processing). And second,
we organize the system in peer-to-peer fashion.
We present the Paderborn University BSP-based Web Computing (PUB-Web) library,
which supports the execution of parallel programs in the bulk-synchronous style
(BSP) in such a web computing setting. In this thesis, we focus on important
technical and algorithmic aspects, in particular: In order to schedule
processes with respect to the currently available computing power, which
continually changes in an unpredictable fashion, we need intelligent load
balancing algorithms and -- as a basic precondition -- the technical ability
to migrate threads at runtime.
To achieve the latter in a way suitable for production use, compatible with
recent Java versions, available for all important platforms, and easy-to-use
for developers, we develop the PadMig thread migration and checkpointing
library.
In order to tackle the distributed load balancing problem, we present an
algorithm based on Distributed Heterogeneous Hash-Tables. In order to judge
the quality of the schedules produced, we perform extensive experiments to
compare several variants of the DHHT-based load balancer with the well-
established Work Stealing algorithm, using realistic input data obtained by
profiling the utilization of several hundred PCs for a period of several
months.
Beside the available computing power, we finally also consider the network
bandwidth as a secondary criterion for load balancing. For this purpose, we
cluster the PUB-Web network according to bandwidth, employing a novel,
fault-tolerant, adaptive, and scaling distributed clustering algorithm called
DiDiC. In order to judge the quality of the clusterings produces by DiDiC,
we experimentally compare it to the well-established MCL algorithm using a
simulator.
AU - Gehweiler, Joachim
ID - 18976
SN - 978-3-942647-17-5
TI - Peer-to-Peer Based Parallel Web Computing
ER -
TY - THES
AU - Suess, Tim
ID - 17454
TI - Parallel Real-Time Rendering using Heterogeneous PC Clusters
ER -
TY - CONF
AU - Suess, Tim
AU - Jähn, Claudius
AU - Fischer, Matthias
AU - Meyer auf der Heide, Friedhelm
AU - Koch, Clemens
ID - 17450
T2 - Augmented & Virtual Reality in der Produktentstehung
TI - Ein paralleles Out-of-Core Renderingsystem für Standard-Rechnernetze
VL - 295
ER -
TY - CONF
AU - Renken, Hendrik
AU - Laroque, Christoph
AU - Fischer, Matthias
ID - 18193
T2 - Proceedings of The 25th European Simulation and Modelling Conference - ESM2011
TI - An Easy Extendable Modeling Framework for Discrete Event Simulation Models and their Visualization
ER -
TY - CONF
AU - Briest, Patrick
AU - Raupach, Christoph
ID - 19026
SN - 9781450307437
T2 - Proceedings of the 23rd ACM symposium on Parallelism in algorithms and architectures - SPAA '11
TI - The car sharing problem
ER -
TY - THES
AU - Effert, Sascha
ID - 19040
TI - Verfahren zur redundanten Datenplatzierung in skalierbaren Speichersystemen
ER -
TY - CONF
AU - Degener, Bastian
AU - Kempkes, Barbara
AU - Langner, Tobias
AU - Meyer auf der Heide, Friedhelm
AU - Pietrzyk, Peter
AU - Wattenhofer, Roger
ID - 16453
SN - 9781450307437
T2 - Proceedings of the 23rd ACM symposium on Parallelism in algorithms and architectures - SPAA '11
TI - A tight runtime bound for synchronous gathering of autonomous robots with limited visibility
ER -
TY - GEN
AB - We present a parallel rendering system for PC-Clusters to visualize large 3D scenes. One single visualization node, equipped with a high-end graphics adapter, is supported by a group of backend nodes with weak graphics performance. The objects of the scene are distributed among these backend nodes, they serve two purposes: First, they provide an out-of-core memory system for the visualization node. Second, they assist the visualization node's rendering by performing visibility calculations and only sending visible objects to the visualization node. In order to obtain fast rendering with our system, we have to distribute the objects among the backend nodes in a way that does not only guarantee an even distribution of the objects, but also an even distribution of the visibility calculations and the amount of data send to the visualization node. We identify necessary properties of the distribution and argue that a random distribution is a good candidate. Further, in order to reduce the number of objects sent to the visualization node per frame, we employ an approximate hierarchical occlusion culling in each backend node. For this, they are equipped, in addition to the objects assigned to them, with simplified versions of the other objects of the 3D scene. The visualization node is equipped with 512 MiB video memory and supported by 15 backend nodes. This system is able to render a approx. 350 million polygons (approx. 8.5 GiB) large aircraft model between 20 - 30 fps and thus allows a walkthrough in real-time.
AU - Suess, Tim
AU - Koch, Clemens
AU - Jähn, Claudius
AU - Fischer, Matthias
AU - Meyer auf der Heide, Friedhelm
ID - 18194
TI - Parallel Out-of-Core Occlusion Culling
ER -
TY - CONF
AB - Occlusion culling is a common approach to accelerate real-time rendering of polygonal 3D-scenes by reducing the rendering load. Especially for large scenes, it is necessary to remove occluded objects to achieve a frame rate that provides an interactive environment. In order to benefit from the culling properly, often hierarchical data structures are used. These data structures typically create a spatial subdivision of a given scene into axis-aligned bounding boxes. These boxes can be tested quickly, but they are not very precise. By using these boxes, the included objects are detected as visible, even if other objects occlude them (false-positives). To get perfect results, the models original geometry included in the box has to be tested, but this would require too much computational power. To overcome this problem, original objects approximations could be used, but typical methods for mesh simplification cannot be applied, because they do not create an outer hull for a given object. We present a model simplification algorithm, which generates simple outer hulls, consisting of only few more triangles than a box, while preserving an objects shape better than a corresponding bounding box. This approach is then extended to a hierarchical data structure, the so-called hull tree, that can be generated for a given scene to improve the visibility tests. Next, we present an approximative rendering algorithm, which combines the features of the hull tree with the use of inner hulls for efficient occlusion detection and global state-sorting of the visible objects.
AU - Süß, Tim
AU - Koch, Clemens
AU - Jähn, Claudius
AU - Fischer, Matthias
ED - Brooks, Stephen
ED - Irani, Pourang
ID - 17420
T2 - Proceedings of the Graphics Interface 2011 Conference, May 25-27, St. John's, Newfoundland, Canada
TI - Approximative occlusion culling using the hull tree
ER -
TY - CHAP
AB - Gathering n mobile robots in one single point in the Euclidean plane is a widely studied problem from the area of robot formation problems. Classically, the robots are assumed to have no physical extent, and they are able to share a position with other robots. We drop these assumptions and investigate a similar problem for robots with (a spherical) extent: the goal is to gather the robots as close together as possible. More exactly, we want the robots to form a sphere with minimum radius around a predefined point. We propose an algorithm for this problem which synchronously moves the robots towards the center of the sphere unless they block each other. In this case, if possible, the robots spin around the center of the sphere. We analyze this algorithm experimentally in the plane. If R is the distance of the farthest robot to the center of the sphere, the simulations indicate a runtime which is linear in n and R. Additionally, we prove a theoretic upper bound for the runtime of O(nR) for a discrete version of the problem. Simulations also suggest a runtime of O(n + R) for the discrete version.
AU - Cord-Landwehr, Andreas
AU - Degener, Bastian
AU - Fischer, Matthias
AU - Hüllmann, Martina
AU - Kempkes, Barbara
AU - Klaas, Alexander
AU - Kling, Peter
AU - Kurras, Sven
AU - Märtens, Marcus
AU - Meyer auf der Heide, Friedhelm
AU - Raupach, Christoph
AU - Swierkot, Kamil
AU - Warner, Daniel
AU - Weddemann, Christoph
AU - Wonisch, Daniel
ID - 16410
SN - 0302-9743
T2 - SOFSEM 2011: Theory and Practice of Computer Science
TI - Collisionless Gathering of Robots with an Extent
ER -
TY - CHAP
AU - Degener, Bastian
AU - Kempkes, Barbara
AU - Kling, Peter
AU - Meyer auf der Heide, Friedhelm
ID - 16365
SN - 0302-9743
T2 - Structural Information and Communication Complexity
TI - A Continuous, Local Strategy for Constructing a Short Chain of Mobile Robots
ER -
TY - BOOK
ED - Abramsky, Samson
ED - Gavoille, Cyril
ED - Kirchner, Claude
ED - Meyer auf der Heide, Friedhelm
ED - Spirakis, Paul G.
ID - 16404
SN - 0302-9743
TI - Automata, Languages and Programming, 37th International Colloquium, ICALP 2010, Bordeaux, France, July 6-10, 2010, Proceedings, Part I.
ER -
TY - GEN
AU - Blesa, Maria J.
AU - Blum, Christian
AU - de Caro, Angelo
AU - Degener, Bastian
AU - Kempkes, Barbara
AU - Leone, Piere
AU - Persiano, Giuseppe
AU - Meyer auf der Heide, Friedhelm
AU - Mylonas, Georgios
ID - 17464
TI - Adapting a sensor net to the dynamic environment in a wildlife scenario - a case study
ER -
TY - CHAP
AB - We present an approach for real-time rendering of complex 3D scenes consisting of millions of polygons on limited graphics hardware. In a preprocessing step, powerful hardware is used to gain fine granular global visibility information of a scene using an adaptive sampling algorithm. Additively the visual influence of each object on the eventual rendered image is estimated. This influence is used to select the most important objects to display in our approximative culling algorithm. After the visibility data is compressed to meet the storage capabilities of small devices, we achieve an interactive walkthrough of the Power Plant scene on a standard netbook with an integrated graphics chipset.
AU - Eikel, Benjamin
AU - Jähn, Claudius
AU - Fischer, Matthias
ID - 16505
SN - 0302-9743
T2 - Advances in Visual Computing
TI - Preprocessed Global Visibility for Real-Time Rendering on Low-End Hardware
ER -
TY - CONF
AB - Many professional cluster systems consist of nodes with different hardware configurations. Such heterogeneous environments require different load-balancing techniques than homogenous environments. The c-load-collision-protocol is able to achieve good results for data-management purposes. Using this protocol, we propose a way for load-balancing in interactive rendering environments. For this work, we implemented a parallel rendering system and took different picking strategies into account to compare the results. The advantage of our approach compared to other approaches is that we group the available nodes of a cluster into two different categories, based on the hardware abilities. Some nodes are used solely for rendering, while others serve as secondary storage and to assist the former ones by performing auxiliary calculations.
AU - Suess, Tim
AU - Wiesemann, Timo
AU - Fischer, Matthias
ID - 18289
SN - 9781424481330
T2 - 2010 IEEE Fifth International Conference on Networking, Architecture, and Storage
TI - Evaluation of a c-Load-Collision-Protocol for Load-Balancing in Interactive Environments
ER -
TY - CONF
AB - Load balancing is an important requirement for the efficient execu-tion of parallel numerical simulations. In particular when the simulation domainchanges over time, the mapping of computational tasks to processors needs tobe modified accordingly. State-of-the-art libraries for this problem are basedon graph repartitioning. They have a number of drawbacks, including the opti-mized metric and the difficulty of parallelizing the popular repartitioning heuris-tic Kernighan-Lin (KL).Here we further explore the very promising diffusion-based graph partitioningalgorithm DIBAP (Meyerhenke et al., JPDC 69(9):750–761, 2009) by adaptingDIBAP to the related problem of load balancing. Experiments with graph se-quences that imitate adaptive numerical simulations demonstrate the applicabilityand high quality of DIBAP for load balancing by repartitioning. Compared to thefaster state-of-the-art repartitioners PARMETIS and parallel JOSTLE, DIBAP’ssolutions have partitions with significantly fewer external edges and boundarynodes and the resulting average migration volume in the important maximumnorm is also the best in most cases.We also prove that one of DIBAP’s key components optimizes a relaxed versionof the minimum edge cut problem. Moreover, we hint at a distributed algorithmbased on ideas used in DIBAP for clustering a virtual P2P supercomputer.
AU - Gehweiler, Joachim
AU - Meyerhenke, Henning
ID - 19016
T2 - Dagstuhl Seminar Proceedings 10261: Algorithm Engineering
TI - On Dynamic Graph Partitioning and Graph Clustering using Diffusion
ER -