computer science publication server: No conditions. Results ordered -Date Deposited. 2021-04-22T23:25:56ZEPrintshttp://e-archive.informatik.uni-koeln.de/images/sitelogo.pnghttp://e-archive.informatik.uni-koeln.de/2016-02-01T12:37:55Z2016-02-01T12:37:55Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/897This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8972016-02-01T12:37:55ZAn Integer Programming Approach to Optimal Basic Block Instruction Scheduling for Single-Issue ProcessorsWe present a novel integer programming formulation for basic block instruction scheduling on single-issue processors. The problem can be considered as a very general sequential task scheduling problem with delayed precedence constraints. Our model is based on the linear ordering problem and has, in contrast to the last IP model proposed, numbers of variables and constraints that are strongly polynomial in the instance size. Combined with improved preprocessing techniques and given a time limit of ten minutes of CPU and system time, our branch-and-cut implementation is capable to solve all but eleven of the 369,861 basic blocks of the SPEC 2000 integer and floating point benchmarks to proven optimality. This is competitive to the current state-of-the art constraint programming approach that has also been evaluated on this test suite.Michael JüngerJünger, MichaelSven MallachMallach, Sven2015-11-03T12:43:35Z2015-11-03T12:43:35Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/895This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8952015-11-03T12:43:35ZPlanar Octilinear Drawings with One Bend Per EdgeIn octilinear drawings of planar graphs, every edge is drawn as a 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 at most 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(n2) ×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 for some edges. Michael A. BekosBekos, Michael A.Martin GronemannGronemann, MartinMichael KaufmannKaufmann, MichaelRobert KrugKrug, Robert2015-07-01T13:04:44Z2015-07-01T13:04:44Zhttp://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, Sven2014-09-05T15:35:13Z2015-11-24T10:41:22Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/878This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8782014-09-05T15:35:13ZThe Landscape Metaphor for Visualization of Molecular SimilaritiesClustered graphs are a versatile representation formalism for expressing relations between entities, and simultaneously, reflecting their hierarchical structure. This makes clustered graphs well-suited to model complex structured data. However, obtaining appealing drawings of clus- tered graphs is a challenging task. We employ the landscape metaphor to visualize clustered graphs in a cheminformatics application. In order to browse chemical compound libraries in a systematic way, we consider two different molecular similarity concepts. Combining the scaffold-based cluster hierarchy with molecular similarity graphs allows for new insights in the analysis of large molecule libraries. Here, like in certain other application domains, the cluster hierarchy does not necessarily reflect the underlying graph structure. We improve the approach taken in [9] by ap- plying a modified treemap algorithm for node positioning that takes the edges of the graph into account. Experiments with real-world instances clearly show that the new algorithm leads to significant improvements in terms of the edge lengths.Martin GronemannGronemann, MartinMichael JüngerJünger, MichaelNils KriegeKriege, NilsPetra MutzelMutzel, Petra2014-09-05T15:34:57Z2014-09-05T15:34:57Zhttp://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, Robert2014-09-05T15:34:37Z2015-11-24T09:47:18Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/876This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8762014-09-05T15:34:37ZPerfect Smooth Orthogonal DrawingsSmooth orthogonal drawings were recently intro- duced with the view of combining two different graph drawing approaches: Orthogonal drawings and Lombardi drawings. In this paper, we focus on perfect smooth orthogonal drawings in which each edge is made of either a rectilinear segment or a circular arc. We prove that every 3-planar graph admits a planar perfect smooth orthogonal drawing. If we relax planarity constraints, we show that every graph of maximum degree 4 admits a (non-planar) perfect smooth orthogonal drawing. We demonstrate that there exist infinitely many planar graphs that do not admit planar perfect smooth orthogonal drawings under the Kandinsky model. Finally, we introduce classes of graphs admitting perfect smooth orthogonal drawings of different styles and study relations between these classes.Michael A. BekosBekos, Michael A.Martin GronemannGronemann, MartinSergey PupyrevPupyrev, SergeyChrysanthi N. RaftopoulouRaftopoulou, Chrysanthi N.2014-09-05T15:34:24Z2015-11-24T09:37:15Zhttp://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, Robert2014-09-03T12:31:37Z2015-11-24T09:32:25Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/874This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8742014-09-03T12:31:37ZBitonic st-orderings of biconnected planar graphsVertex orderings play an important role in the design of graph drawing algorithms.
Compared to canonical orderings, st-orderings lack a certain property that is required by many drawing methods.
In this paper, we propose a new type of st-ordering for biconnected planar graphs that relates the ordering to the embedding.
We describe a linear-time algorithm to obtain such an ordering and demonstrate its capabilities with two applications.Martin GronemannGronemann, Martin2014-06-16T13:23:32Z2014-06-16T13:23:32Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/804This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8042014-06-16T13:23:32ZOptimal general offset assignmentWe present an exact approach to the General Offset Assign-
ment problem arising in the domain of address code gen-
eration for application specific and digital signal processors.
General Offset Assignment is composed of two subproblems,
namely to find a permutation of variables in memory and to select a responsible address register for each access to one of these variables. Our method is a combination of established techniques to solve both subproblems using integer linear programming. To the best of our knowledge, it is the first approach capable of solving almost all instances of the established OffsetStone benchmark set to global optimality within reasonable time. We provide a first comprehensive evaluation of the quality of several state-of-the-art heuristics relative to the optimal solutions.Sven MallachMallach, SvenRoberto Castañeda LozanoLozano, Roberto Castañeda2014-06-11T11:26:26Z2014-06-11T11:26:26Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/801This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8012014-06-11T11:26:26ZTwo-Page Book Embeddings of 4-Planar GraphsBack in the eighties, Heath showed that every 3-planar graph is subhamiltonian and asked whether this result can be extended to a class of graphs of degree greater than three. In this paper we affirmatively answer this question for the class of 4-planar graphs. Our contribution consists of two algorithms: The first one is limited to triconnected graphs, but runs in linear time and uses existing methods for computing hamiltonian cycles in planar graphs. The second one, which solves the general case of the problem, is a quadratic-time algorithm based on the book embedding viewpoint of the problem. Michael A. BekosBekos, Michael A.Martin GronemannGronemann, MartinChrysanthi N. RaftopoulouRaftopoulou, Chrysanthi N.2014-06-11T11:25:11Z2014-06-16T13:25:03Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/802This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/8022014-06-11T11:25:11ZTwo-Page Book Embeddings of 4-Planar Graphs (Extended Draft Version)Back in the Eighties, Heath showed that every 3-planar graph is subhamiltonian and asked whether this result can be extended to a class of graphs of degree greater than three. In this paper we affirmatively answer this question for the class of 4-planar graphs. Our contribution consists of two algorithms: The first one is limited to triconnected graphs, but runs in linear time and uses existing methods for computing hamiltonian cycles in planar graphs. The second one, which solves the general case of the problem, is a quadratic-time algorithm based on the book-embedding viewpoint of the problem. Michael A. BekosBekos, Michael A.Martin GronemannGronemann, MartinChrysanthi N. RaftopoulouRaftopoulou, Chrysanthi N.2013-09-02T11:03:41Z2018-03-13T09:35:07Zhttp://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, Petra2013-05-29T07:33:22Z2013-09-02T11:07:17Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/700This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/7002013-05-29T07:33:22ZSolving the Simple Offset Assignment Problem as a Traveling SalesmanIn this paper, we present an exact approach to the Simple Offset Assignment problem arising in the domain of address code generation for digital signal processors. It is based on transformations to weighted Hamiltonian cycle problems and integer linear programming. To the best of our knowledge, it is the first approach capable to solve all instances of the established OffsetStone benchmark set to optimality within reasonable time. Therefore, it enables to evaluate the quality of several heuristics relative to the optimum solutions for the first time. Further, using the same transformations, we present a simple and effective improvement heuristic. In addition, we include an existing heuristic into our experiments that has so far not been evaluated with OffsetStone.Michael JüngerJünger, MichaelSven MallachMallach, Sven2010-11-25T00:00:00Z2012-01-09T14:11:37Zhttp://e-archive.informatik.uni-koeln.de/id/eprint/609This item is in the repository with the URL: http://e-archive.informatik.uni-koeln.de/id/eprint/6092010-11-25T00:00:00ZPreprocessing Maximum Flow AlgorithmsMaximum-flow problems occur in a wide range of applications. Although already well-studied, they are still an area of active research. The fastest available implementations for determining maximum flows in graphs are either based on augmenting-path or on push-relabel algorithms. In this work, we present two ingredients that, appropriately used, can considerably speed up these methods. On the one hand, we present flow-conserving conditions under which subgraphs can be contracted to a single node. These rules are in the same spirit as presented by Padberg and Rinaldi (Math. Programming (47), 1990) for the minimum cut problem in graphs. On the other hand, we propose a two-step max-flow algorithm for solving the problem on instances coming from physics and computer vision. In the two-step algorithm flow is first sent along augmenting paths of restricted lengths only. Starting from this flow, the problem is then solved to optimality using some known max-flow methods. By extensive experiments on random instances and on instances coming from applications in theoretical physics and in computer vision, we show that a suitable combination of the proposed techniques speeds up traditionally used methods.Frauke LiersLiers, FraukeGregor PardellaPardella, Gregor