computer science publication server: No conditions. Results ordered -Date Deposited. 2021-04-22T23:29:27ZEPrintshttp://e-archive.informatik.uni-koeln.de/images/sitelogo.pnghttp://e-archive.informatik.uni-koeln.de/2018-03-12T14:21:45Z2018-03-13T09:36:04Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/924This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/9242018-03-12T14:21:45ZCrossing Minimization in Storyline VisualizationA storyline visualization is a layout that represents the temporal dynamics of social interactions along time by the convergence of chronological lines. Among the criteria oriented at improving aesthetics and legibility of a representation of this type, a small number of line crossings is the hardest to achieve. We model the crossing minimization in the storyline visualization problem as a multi-layer crossing minimization problem with tree constraints. Our algorithm can compute a layout with the minimum number of crossings of the chronological lines. Computational results demonstrate that it can solve instances with more than 100 interactions and with more than 100 chronological lines to optimality.Martin GronemannGronemann, MartinMichael JüngerJünger, MichaelFrauke LiersLiers, FraukeFrancesco MambelliMambelli, Francesco2018-03-12T14:18:42Z2018-03-12T15:06:53Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/922This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/9222018-03-12T14:18:42ZAlgorithms for Incremental Planar Graph Drawing and Two-page Book EmbeddingsSubject of this work are two problems related to ordering the vertices of planar graphs. The first one is concerned with the properties of vertex-orderings that serve as a basis for incremental drawing algorithms. Such a drawing algorithm usually extends a drawing by adding the vertices step-by-step as provided by the ordering. In the field of graph drawing several orderings are in use for this purpose. Some of them, however, lack certain properties that are desirable or required for classic incremental drawing methods. We narrow down these properties, and introduce the bitonic st-ordering, an ordering which combines the features only available when using canonical orderings with the flexibility of st-orderings. The additional property of being bitonic enables an st-ordering to be used in algorithms that usually require a canonical ordering. With this in mind, we describe a linear-time algorithm that computes such an ordering for every biconnected planar graph. Unlike canonical orderings, st-orderings extend to directed graphs, in particular planar st-graphs. Being able to compute bitonic st-orderings for planar st-graphs is of particular interest for upward planar drawing algorithms, since traditional incremental algorithms for undirected planar graphs might be adapted to directed graphs. Based on this observation, we give a full characterization of the class of planar st-graphs that admit such an ordering. This includes a linear-time algorithm for recognition and ordering. Furthermore, we show that by splitting specific edges of an instance that is not part of this class, one is able to transform it into one for which then such an ordering exists. To do so, we describe a linear-time algorithm for finding the smallest set of edges to split. We show that for a planar st-graph G=(V,E), |V|−3 edge splits are sufficient and every edge is split at most once. This immediately translates to the number of bends required for upward planar poly-line drawings. More specifically, we show that every planar st-graph admits an upward planar poly-line drawing in quadratic area with at most |V|−3 bends in total and at most one bend per edge. Moreover, the drawing can be obtained in linear time. The second part is concerned with embedding planar graphs with maximum degree three and four into books. Besides providing a simplified incremental linear-time algorithm for embedding triconnected 3-planar graphs into a book of two pages, we describe a linear-time algorithm to compute a subhamiltonian cycle in a triconnected 4-planar graph.Martin GronemannGronemann, Martin2015-11-03T13:12:07Z2015-11-03T13:12:07Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/890This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8902015-11-03T13:12:07ZSmall Molecule Subgraph Detector (SMSD) toolkitSyed Asad Rahman Rahman , Syed AsadMatthew BashtonBashton, MatthewGemma L. HollidayHolliday, Gemma L.Rainer SchraderSchrader, RainerJanet M. ThorntonThornton, Janet M.2015-09-14T13:08:27Z2015-09-24T14:15:41Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/884This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8842015-09-14T13:08:27ZThe team priority assignment problemMatthias LohmannLohmann, MatthiasOliver UllrichUllrich, OliverManuel Molina MadridMolina Madrid, ManuelDaniel LückerathLückerath, DanielEwald SpeckenmeyerSpeckenmeyer, Ewald2015-07-01T13:04:44Z2015-07-01T13:04:44Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/883This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8832015-07-01T13:04:44ZMore General Optimal Offset AssignmentThis manuscript presents exact approaches to the general offset assignment problem arising in the address code generation phase of compilers for application-specific processors. First, integer programming models for architecture-dependent and theoretically motivated special cases of the problem are established. Then, these models are extended to provide the first widely applicable formulations for the most general problem setting, supporting processors with several address registers and complex addressing capabilities. Existing heuristics are
similarly extended and practical applicability of the proposed methods is demonstrated by experimental evaluation using an established and large benchmark set. The experiments allow us to study the impact of exploiting more complex memory addressing capabilities on the address computation costs of real-world programs. We also show how to integrate operand reordering techniques for commutative instructions into existing solution approaches.Sven MallachMallach, Sven2015-05-20T14:50:20Z2015-05-20T14:50:20Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/882This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8822015-05-20T14:50:20ZExact Integer Programming Approaches to Sequential Instruction Scheduling and Offset AssignmentThe dissertation at hand presents the main concepts and results derived when studying the optimal solution of two NP-hard compiler optimization problems, namely instruction scheduling and offset assignment, by means of integer programming. It is the outcome of several years of research as an assistant at Michael Jünger's computer science chair in Cologne, with the particular aim to apply exact mathematical optimization techniques to real-world problems arising in the domain of technical computer science. The two problems studied are rather unrelated apart from the fact that they both take place during the machine code generation phase of a compiler and deal with the handling of limited resources. Instruction scheduling is about the assignment of issue clock cycles to instructions in the presence of precedence, latency, and resource constraints such that the total time needed to execute all the instructions is minimized. Offset assignment deals with storage layouts of program variables and the efficient use of address registers for accesses to these variables. The objective is to employ specialized instructions in order to minimize the overhead caused by address computations. While instruction scheduling needs to be carried out by almost every present compiler irrespective of the processor architecture, the offset assignment problem occurs mainly in compilers for highly specialized processor designs. Instruction scheduling is a well-studied field where several exact and heuristic approaches have been developed and experimentally evaluated in the past. In this thesis, we concentrate on the basic-block instruction scheduling problem for single-issue processors. Basic blocks are program fragments with no side-entrances and -exits, i.e., every instruction of a basic block needs to be executed before the control flow may leave it and enter another basic block. Single-issue processors are capable of starting the execution of exactly one instruction per clock cycle. A number of techniques to preprocess instances of the basic-block instruction scheduling problem were proposed in the literature and are, with emphasis on the more recent ones that arose since the year 2000, thoroughly reviewed in this thesis. They finally led to a constraint programming approach in 2006 that was shown to solve about 350,000 instances to optimality and where some of these instances comprised up to about 2,500 instructions. The last attempt to tackle the problem using integer programming however dates to a time prior to the publication of the latest preprocessing advances. While being successful on a set of instances that impose very restrictive latency constraints, it was shown to be unable to solve hundreds of instances from the aforementioned benchmark set that comprises also large and varying latencies. In addition, the previous integer programming models were almost all based on so-called time-indexed formulations where decision variables model an explicit assignment of instructions to clock cycles. In this thesis, a completely different and novel approach is taken based on the linear ordering problem, a well-studied combinatorial optimization problem. The new models lead to alternative characterizations of the feasible solutions to the basic-block instruction scheduling problem. These facilitate the employment of advanced integer programming methodologies, in particular the design of branch-and-cut algorithms that can handle larger instances. The formulations are further extended by additional inequalities that can be used as cutting planes. Combined with the preprocessing routines that are partially extended and improved as well, the respective solver implementation eventually turned out to be competitive to the constraint programming method. Reaching this point has taken some years and this thesis presents not only the derived models but also several ideas and byproducts that arose in the meantime, and that can help and inspire researchers even if they aim at the application of different solution methodologies. The starting point regarding the offset assignment problem was a different one because especially exact solution approaches were rather rare prior to the models presented in this thesis. The offset assignment problem arose in the 1990s and is considered in several variants that are of theoretical and practical interest. In the simplest one, a processor is assumed to provide only a single address register and only very restricted possibilities to avoid address computation overhead. However, even this simplest variant, that may serve as a building block for the more complex ones, is already NP-hard and has been studied mainly from a heuristic point of view. The few existing exact solution approaches were not capable to solve moderately sized instances so that the quality of heuristic solutions relative to the optimum was hardly known at all. Again, the inspection of the combinatorial structure of the various problem variants turned out to be the key for designing branch-and-cut implementations that can profit from knowledge about related combinatorial optimization problems. The implementation targeting the simple problem variant was the first capable to optimally solve the majority of about 3,000 instances collected in a standard benchmark set. The method could then be further generalized in two steps. First, in a collaboration with Roberto Castañeda Lozano, additional techniques could be incorporated into the approach in order to handle multiple address registers. Fortunately, the methods could then even be further extended to as well deal with more flexible addressing capabilities. In this way, the thesis at hand does not only answer the question how large the address computation overhead can be when using heuristics, but as well presents first results that allow to analyze the impact of the mentioned increased addressing capabilities on the runtime performance and size of real-world programs.Sven MallachMallach, Sven2014-09-05T15:34:57Z2014-09-05T15:34:57Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/877This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8772014-09-05T15:34:57ZPlanar Octilinear Drawings with One Bend Per Edge (Extended Draft Version)In octilinear drawings of planar graphs, every edge is drawn as an alternating sequence of horizontal, vertical and diagonal (45°) line-segments. In this paper, we study octilinear drawings of low edge complexity, i.e., with few bends per edge. A k-planar graph is a planar graph in which each vertex has degree less or equal to k. In particular, we prove that every 4-planar graph admits a planar octilinear drawing with at most one bend per edge on an integer grid of size O(n^2)×O(n). For 5-planar graphs, we prove that one bend per edge still suffices in order to construct planar octilinear drawings, but in super-polynomial area. However, for 6-planar graphs we give a class of graphs whose planar octilinear drawings require at least two bends per edge. Michael A. BekosBekos, Michael A.Martin GronemannGronemann, MartinMichael KaufmannKaufmann, MichaelRobert KrugKrug, Robert2014-09-05T15:34:24Z2015-11-24T09:37:15Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/875This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8752014-09-05T15:34:24ZPlanar Octilinear Drawings with One Bend Per EdgeIn octilinear drawings of planar graphs, every edge is drawn as an alternating sequence of horizontal, vertical and diagonal (45°) line-segments. In this paper, we study octilinear drawings of low edge complexity, i.e., with few bends per edge. A k-planar graph is a planar graph in which each vertex has degree less or equal to k. In particular, we prove that every 4-planar graph admits a planar octilinear drawing with at most one bend per edge on an integer grid of size O(n^2)×O(n). For 5-planar graphs, we prove that one bend per edge still suffices in order to construct planar octilinear drawings, but in super-polynomial area. However, for 6-planar graphs we give a class of graphs whose planar octilinear drawings require at least two bends per edge. Michael A. BekosBekos, Michael A.Martin GronemannGronemann, MartinMichael KaufmannKaufmann, MichaelRobert KrugKrug, Robert2014-03-14T08:04:55Z2014-03-14T08:04:55Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/770This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/7702014-03-14T08:04:55ZMulti-depot multi-vehicle-type vehicle scheduling for Cologne’s tram network
To be a feasible base for simulation studies of Cologne's tram network, a valid vehicle schedule has to con-sider several requirements, like multiple vehicle depots and multiple types of vehicles. The local transport provider utilizes both low-floor and high-floor vehicles, with high-floor vehicles being qualified to serve both high-floor and low-floor platforms. Therefore mixed vehicle rotations are acceptable, but generally not desired. This paper presents a set of models which adhere to these requirements, while also considering sev-eral possible optimization goals, like minimum number of deployed vehicles, and minimum combined length of maintenance trips.Daniel LückerathLückerath, DanielOliver UllrichUllrich, OliverAleksander KupichaKupicha, AleksanderEwald SpeckenmeyerSpeckenmeyer, Ewald2013-09-02T11:03:41Z2018-03-13T09:35:07Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/705This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/7052013-09-02T11:03:41ZAlgorithm Engineering im GraphenzeichnenAnhand zweier Beispiele illustrieren wir die Anwendung von Algorithm Engineering im Bereich des automatischen Zeichnens von Graphen. Zunächst berichten wir über die Planarisierungsmethode und zeichnen ihre Entwicklung in den letzten ca. 10 Jahren nach. Dann widmen wir uns der Darstellung von Clustergraphen als topographische Karten, einem Thema, mit dem wir uns erst seit kurzem beschäftigen. Schließlich geben wir einen Ausblick auf eine mögliche Zusammenführung dieser scheinbar zusammenhanglosen Gebiete des automatischen Zeichnens von Graphen. Ein Großteil der hier beschriebenen Entwicklungen wurde von der DFG im Rahmen des SPP 1307 bzw. vorangegangenen Schwerpunktprogrammen gefördert. Martin GronemannGronemann, MartinCarsten GutwengerGutwenger, CarstenMichael JüngerJünger, MichaelPetra MutzelMutzel, Petra2012-12-04T13:29:38Z2014-04-09T14:37:41Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/688This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/6882012-12-04T13:29:38ZMolMap - Visualizing Molecule Libraries as Topographic MapsWe present a new application for graph drawing and visualization in the context of drug discovery. Combining the scaffold-based cluster hierarchy with molecular similarity graphs — both standard concepts in cheminfor- matics — allows one to get new insights for analyzing large molecule libraries. The derived clustered graphs represent different aspects of structural similarity. We suggest visualizing them as topographic maps. Since the cluster hierarchy does not reflect the underlying graph structure as in (Gronemann and Jünger, 2012), we suggest a new partitioning algorithm that takes the edges of the graph into account. Experiments show that the new algorithm leads to significant improvements in terms of the edge lengths in the obtained drawings.Martin GronemannGronemann, MartinMichael JüngerJünger, MichaelPetra MutzelMutzel, PetraNils KriegeKriege, Nils2012-09-05T06:41:50Z2015-11-24T12:03:52Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/685This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/6852012-09-05T06:41:50ZSolving k-way Graph Partitioning Problems to
Optimality: The Impact of Semidefinite
Relaxations and the Bundle MethodThis paper is concerned with computing global optimal solutions for maximum k-cut problems. We improve on the SBC algorithm of Ghaddar, Anjos and Liers in order to compute such solutions in less time. We extend the design principles
of the successful BiqMac solver for maximum 2-cut to the general maximum k-cut problem. As part of this extension, we investigate different ways of choosing variables for branching.We also study the impact of the separation of clique inequalities within this new framework and observe that it frequently reduces the number of subproblems considerably. Our computational results suggest that the proposed approach achieves a drastic speedup in comparison to SBC, especially when k = 3. We also made a comparison with the orbitopal fixing approach of Kaibel, Peinhardt and Pfetsch. The results suggest that while their performance is better for sparse instances and larger values of k, our proposed approach is superior for smaller k and for dense instances of medium size. Furthermore, we used CPLEX for solving the ILP formulation underlying the orbitopal fixing algorithm and conclude that especially on dense instances the new algorithm outperforms CPLEX by far.Miguel AnjosAnjos, MiguelBissan GhaddarGhaddar, BissanLena HuppHupp, LenaFrauke LiersLiers, FraukeAngelika WiegeleWiegele, Angelika