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  • 301.
    Jonsson, Peter
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Lagerkvist, Victor
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Schmidt, Johannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Uppman, Hannes
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Relating the Time Complexity of Optimization Problems in Light of the Exponential-Time Hypothesis2014In: Mathematical Foundations of Computer Science 2014: 39th International Symposium, MFCS 2014, Budapest, Hungary, August 25-29, 2014. Proceedings, Part II / [ed] Erzsébet Csuhaj-Varjú, Martin Dietzfelbinger, Zoltán Ésik, Springer Berlin/Heidelberg, 2014, p. 408-419Chapter in book (Refereed)
    Abstract [en]

    Obtaining lower bounds for NP-hard problems has for a long time been an active area of research. Recent algebraic techniques introduced by Jonsson et al. (SODA 2013) show that the time complexity of the parameterized SAT(·) problem correlates to the lattice of strong partial clones. With this ordering they isolated a relation R such that SAT(R) can be solved at least as fast as any other NP-hard SAT(·) problem. In this paper we extend this method and show that such languages also exist for the max ones problem (Max-Ones(Γ)) and the Boolean valued constraint satisfaction problem over finite-valued constraint languages (VCSP(Δ)). With the help of these languages we relate Max-Ones and VCSP to the exponential time hypothesis in several different ways.

  • 302.
    Jonsson, Peter
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Lagerkvist, Viktor
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Nordh, Gustav
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Zanuttini, Bruno
    Université de Caen Basse-Normandie, France.
    Complexity of SAT problems, Clone Theory and the Exponential Time Hypothesis2013In: SODA-2013, SIAM , 2013, p. 1264-1277Conference paper (Refereed)
  • 303.
    Jonsson, Peter
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Lööw, Tomas
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Computational complexity of linear constraints over the integers2013In: Artificial Intelligence, ISSN 0004-3702, E-ISSN 1872-7921, Vol. 195, p. 44-62Article in journal (Refereed)
    Abstract [en]

    Temporal reasoning problems arise in many areas of Al, including planning, natural language understanding, and reasoning about physical systems. The computational complexity of continuous-time temporal constraint reasoning is fairly well understood. There are, however, many different cases where discrete time must be considered; various scheduling problems and reasoning about sampled physical systems are two examples. Here, the complexity of temporal reasoning is not as well-studied nor as well-understood. In order to get a better understanding, we consider the powerful Horn disjunctive linear relations (Horn DLR) formalism adapted for discrete time and study its computational complexity. We show that the full formalism is NP-hard and identify several maximal tractable subclasses. We also lift the maximality results to obtain hardness results for other families of constraints. Finally, we discuss how the results and techniques presented in this paper can be used for studying even more expressive classes of temporal constraints.

  • 304.
    Jonsson, Peter
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Thapper, Johan
    Université Paris-Sud 11, Laboratoire de Recherche en Informatique (LRI) .
    Affine Consistency and the Complexity of Semilinear Constraints2014In: Mathematical Foundations of Computer Science 2014 / [ed] Ersébet Csuhaj-Varjú,Martin Dietzfelbinger,Zoltán Ésik, Berlin/Heidelberg, 2014, p. 420-431Conference paper (Refereed)
    Abstract [en]

    A semilinear relation is a finite union of finite intersections of open and closed half-spaces over, for instance, the reals, the rationals or the integers. Semilinear relations have been studied in connection with algebraic geometry, automata theory, and spatiotemporal reasoning, just to mention a few examples. We concentrate on relations over the reals and rational numbers. Under this assumption, the computational complexity of the constraint satisfaction problem (CSP) is known for all finite sets Γ of semilinear relations containing the relations R +={(x,y,z) | x+y=z}, ≤ and {1}. These problems correspond to extensions of LP feasibility. We generalise this result as follows. We introduce an algorithm, based on computing affine hulls, which solves a new class of semilinear CSPs in polynomial time. This allows us to fully determine the complexity of CSP(Γ) for semilinear Γ containing R+ and satisfying two auxiliary conditions. Our result covers all semilinear Γ such that {R+,{1}}⊆Γ. We continue by studying the more general case when Γ contains R+ but violates either of the two auxiliary conditions. We show that each such problem is equivalent to a problem in which the relations are finite unions of homogeneous linear sets and we present evidence that determining the complexity of these problems may be highly non-trivial.

  • 305.
    Jonsson, Peter
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Thapper, Johan
    University of Paris Est Marne la Vallee, France.
    Constraint satisfaction and semilinear expansions of addition over the rationals and the reals2016In: Journal of computer and system sciences (Print), ISSN 0022-0000, E-ISSN 1090-2724, Vol. 82, no 5, p. 912-928Article in journal (Refereed)
    Abstract [en]

    A semilinear relation is a finite union of finite intersections of open and closed half spaces over, for instance, the reals, the rationals, or the integers. Semilinear relations have been studied in connection with algebraic geometry, automata theory, and spatiotemporal reasoning. We consider semilinear relations over the rationals and the reals. Under this assumption, the computational complexity of the constraint satisfaction problem (CSP) is known for all finite sets containing R+ = {(x, y, z) vertical bar x y = z}, <=, and {1}. These problems correspond to expansions of the linear programming feasibility problem. We generalise this result and fully determine the complexity for all finite sets of semilinear relations containing R+. This is accomplished in part by introducing an algorithm, based on computing affine hulls, which solves a new class of semilinear CSPs in polynomial time. We further analyse the complexity of linear optimisation over the solution set and the existence of integer solutions. (C) 2016 Elsevier Inc. All rights reserved.

  • 306.
    Jonsson, Peter
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Thapper, Johan
    Univ Paris Est Marne la Vallee, France.
    Tractability conditions for numeric CSPs2018In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 715, p. 21-34Article in journal (Refereed)
    Abstract [en]

    The computational complexity of the constraint satisfaction problem (CSP) with semilinear relations over the reals has gained recent attraction. As a result, its complexity is known for all finite sets of semilinear relations containing the relation R+ = {(x, y, z) is an element of R-3 vertical bar x + y = z}. We consider larger and more expressive classes of relations such as semialgebraic and o-minimal relations. We present a general result for characterising computationally hard fragments and, under certain side conditions, this result implies that polynomial-time solvable fragments are only to be found within two limited families of sets of relations. In the setting of semialgebraic relation, our result takes on a simplified form and we provide a full complexity classification for constraint languages that consist of algebraic varieties. Full classifications like the one obtained here for algebraic varieties or the one for semilinear relations appear to be rare and we discuss several barriers for obtaining further such results. These barriers have strong connections with well-known open problems concerning the complexity of various restrictions of convex programming. (c) 2018 Elsevier B.V. All rights reserved.

  • 307.
    Joshi, Prachi
    et al.
    Virginia Tech, VA 24061 USA.
    Ravi, S. S.
    Virginia Tech, VA 24061 USA; SUNY Albany, NY 12222 USA.
    Samii, Soheil
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering. Gen Motors, MI USA.
    Bordoloi, Unmesh D.
    Gen Motors, MI USA.
    Shukla, Sandeep K.
    IIT Kanpur, India.
    Zeng, Haibo
    Virginia Tech, VA 24061 USA.
    Offset Assignment to Signals for Improving Frame Packing in CAN-FD2017In: 2017 IEEE REAL-TIME SYSTEMS SYMPOSIUM (RTSS), IEEE , 2017, p. 167-177Conference paper (Refereed)
    Abstract [en]

    Controller Area Network (CAN) is a widely used protocol that allows communication among Electronic Control Units (ECUs) in automotive electronics. It was extended to CAN-FD (CAN with Flexible Data-rate) to meet the increasing demand for bandwidth utilization caused by the growing number of features in modern automobiles. The signal-to-frame packing problem has been studied in literature for both CAN and CAN-FD. In this work, we propose and formulate, for the first time, the signal offset assignment problem (SOAP) in a frame in order to improve the bus bandwidth utilization. We prove that SOAP is NP-complete. We propose a general approximation framework (GAF) for SOAP which can use any approximation algorithm for the makespan minimization problem (MMP) in multiprocessor systems. We derive the performance guarantee provided by GAF as a function of the performance guarantee of the approximation algorithm for MMP and the number of signal periods in the frame. We demonstrate the efficacy of our approach through experiments using three different algorithms (two approximation algorithms and an integer linear programming formulation) for MMP in GAF. Our results indicate that by using offsets for signals in frame packing schemes, one can achieve about 10.54% improvement in bandwidth utilization (on a single bus) in CAN-FD systems.

  • 308.
    Joshi, Prachi
    et al.
    Virginia Tech, Blacksburg, VA, USA.
    Zeng, Haibo
    Virginia Tech, Blacksburg, VA, USA.
    Bordoloi, Unmesh D.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering. General Motors, USA.
    Samii, Soheil
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering. General Motors, USA.
    Ravi, S. S.
    Virginia Tech,Blacksburg, VA, USA.
    Shukla, Sandeep K.
    IT Kanpur, Kanpur, India.
    The Multi-Domain Frame Packing Problem for CAN-FD2017In: 29th Euromicro Conference on Real-Time Systems (ECRTS 2017), Schloss Dagstuhl--Leibniz-Zentrum fuer Informatik , 2017Conference paper (Refereed)
    Abstract [en]

    The Controller Area Network with Flexible Data-Rate (CAN-FD) is a new communication protocol to meet the bandwidth requirements for the constantly growing volume of data exchanged in modern vehicles. The problem of frame packing for CAN-FD, as studied in the literature, assumes a single sub-system where one CAN-FD bus serves as the communication medium among several Electronic Control Units (ECUs). Modern automotive electronic systems, on the other hand, consist of several sub-systems, each facilitating a certain functional domain such as powertrain, chassis and suspension. A substantial fraction of all signals is exchanged across sub-systems. In this work, we study the frame packing problem for CAN-FD with multiple sub-systems, and propose a two-stage optimization framework. In the first stage, we pack the signals into frames with the objective of minimizing the bandwidth utilization. In the second stage, we extend Audsley's algorithm to assign priorities/identifiers to the frames. In case the resulting solution is not schedulable, our framework provides a potential repacking method. We propose two solution approaches: (a) an Integer Linear Programming (ILP) formulation that provides an optimal solution but is computationally expensive for industrial-size problems; and (b) a greedy heuristic that scales well and provides solutions that are comparable to optimal solutions. Experimental results show the efficiency of our optimization framework in achieving feasible solutions with low bandwidth utilization. The results also show a significant improvement over the case when there is no cross-domain consideration (as in prior work).

  • 309.
    Kalns, Gundars
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Nadjm-Tehrani, Simin
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Vasilevskaya, Maria
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Trading off Latency against Security in Open Energy Metering Infrastructures2016In: Proceedings of The 4th International Symposium for Industrial Control Systems and SCADA Cyber Security (ICS-CSR), British Computer Society (BCS), 2016Conference paper (Refereed)
    Abstract [en]

    Embedded devices are expected to transform the landscape of networked services in many domains, among them smart homes and smart grid systems. The reliable and optimised operation of smart grids is dependent on reliable data provided by end nodes (e.g. smart meters), and assurance of secure communication across networks. Understanding whether advanced security building blocks have a role to play in forthcoming infrastructures needs a basic understanding of each potential building block with respect to resource usage and impact on timing. In this paper we study the performance penalty of asymmetric cryptography techniques used for protection of wirelessly transmitted data in a prototype smart metering system. The prototype system is built using hardware and software components from “Open Energy Monitor” project using a wireless data link between the metering device and the data collector device. We investigate the use of the Elliptic Curve Integrated Encryption Scheme (ECIES) in two versions - with standard building blocks and with added Elliptic Curve Digital Signature Algorithm (ECDSA) support. The use of the ECDSA allows the system to achieve the non-repudiation property. We compare those cryptographic techniques with the Advanced Encryption Standard in Galois Counter Mode (AES-GCM) technique in two versions - with 128 bit and 256 bit keys. Performance is compared in terms of execution time of (1) preparing data, (2) unpacking it, and (3) roundtrip time. We then discuss the implications of the measurements, where the roundtrip time of sending one measurement ranges from 378 ms in case of AES128-GCM to 16.3 sec using ECIES with ECDSA.

  • 310.
    Karlsson, Jonathan
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Network protocol for distribution and handling of data from JAS 39 Gripen2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    On board the aircraft JAS 39 Gripen a measuring system, Data Acquisition System (DAS), is sending sensor data to a server on the ground. In this master thesis, a unified API for distribution and handling of the sensor data is designed and implemented. The work has been carried out at Saab Aeronautics, Linköping during, 2014.

    During flights with the aircraft the engineers at Saab need to monitor different sensors in the aircraft, including the exact commands of the pilots. All that data is serialized and sent via radio link to a server at Saab. The current data distribution solution includes several clients that need to connect to the server. Each client has its own connection protocol, making the system complex and difficult to maintain. An API is needed in order to make the clients connect in a unified manner. This would also enable future clients to implement the API and start receiving sensor data from the server.

    The research conducted in the thesis project was centered on the different choices that exist for designing such an API. The question that needed answering was; how can an existing complex system can be replaced by a publish-subscribe system and what the benefits would be in terms of latency and flexibility of the system? The design would have to be flexible enough to support multiple clients. The investigated research question was answered with a design utilizing ZMQ, pthreads and a design pattern. The result is a flexible system that was sufficiently fast for the requirements set at Saab and open to future extensions.

    The thesis work also included designing a unified API with requirements on latency and functionality. The resulting API was designed using the publish-subscribe design pattern, the network library Zero Message Queue (ZMQ) and the threading library pthreads. The resulting system supports multiple coexisting servers and clients that request sensor data. A new feature is that the clients can start sending calculations performed on samples to other clients.

    To demonstrate that the solution provides a unified framework, two existing clients and the server were developed with the proposed API. To test the latency requirements, tests were performed in the control room at Saab. 

  • 311.
    Kastegård, Sandra
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Automated testing of a web-based user interface2015Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    Testing is a vital part of software development and test automation is an increasingly common practise. Performing automated testing on web-based applications is more complicated than desktop applications, which is particularly clear when it comes to testing a web based user interface as they are becoming more complex and dynamic. Depending on the goals and needed complexity of the testing, a variety of different frameworks/tools are available to help implementing it.

    This thesis investigates how automated testing of a web-based user interface can be implemented. Testing methods and a selection of relevant testing frameworks/tools are presented and evaluated based on given requirements. Out of the selected frameworks/tools, the Selenium WebDriver framework is chosen and used for implementation. The implementation results in automated test cases for regression testing of the functionality of a user interface created by Infor AB.

  • 312.
    Keller, Jörg
    et al.
    FernUniversität in Hagen, Germany.
    Kessler, Christoph W.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Hultén, Rikard
    Linköping University, Department of Computer and Information Science. Linköping University, The Institute of Technology.
    Optimized On-Chip-Pipelining for Memory-Intensive Computations on Multi-Core Processors with Explicit Memory Hierarchy2012In: Journal of Universal Computer Science, ISSN 0948-695X, Vol. 18, no 14, p. 1987-2023Article in journal (Refereed)
    Abstract [en]

    Limited bandwidth to off-chip main memory tends to be a performance bottleneck in chip multiprocessors, and this will become even more problematic with an increasing number of cores. Especially for streaming computations where the ratio between computational work and memory transfer is low, transforming the program into more memory-efficient code is an important program optimization.

    On-chip pipelining reorganizes the computation so that partial results of subtasks are forwarded immediately between the cores over the high-bandwidth internal network, in order to reduce the volume of main memory accesses, and thereby improves the throughput for memory-intensive computations. At the same time, throughput is also constrained by the limited amount of on-chip memory available for buffering forwarded data. By optimizing the mapping of tasks to cores, balancing a trade-off between load balancing, buffer memory consumption, and communication load on the on-chip network, a larger buffer size can be applied, resulting in less DMA communication and scheduling overhead.

    In this article, we consider parallel mergesort as a representative memory-intensive application in detail, and focus on the global merging phase, which is dominating the overall sorting time for larger data sets. We work out the technical issues of applying the on-chip pipelining technique, and present several algorithms for optimized mapping of merge trees to the multiprocessor cores. We also demonstrate how some of these algorithms can be used for mapping of other streaming task graphs.

    We describe an implementation of pipelined parallel mergesort for the Cell Broadband Engine, which serves as an exemplary target. We evaluate experimentally the influence of buffer sizes and mapping optimizations, and show that optimized on-chip pipelining indeed speeds up, for realistic problem sizes, merging times by up to 70% on QS20 and 143% on PS3 compared to the merge phase of CellSort, which was by now the fastest merge sort implementation on Cell.

  • 313.
    Keller, Jörg
    et al.
    FernUniversität in Hagen, Germany.
    Majeed, Mudassar
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Balancing CPU Load for Irregular MPI Applications2012In: Advances in Parallel Computing: Applications, Tools and Techniques on the Road to Exascale Computing / [ed] Koen De Bosschere, Erik H. D'Hollander, Gerhard R. Joubert, David Padua, Frans Peters, Mark Sawyer, IOS Press, 2012, p. 307-316Conference paper (Refereed)
    Abstract [en]

    MPI applications typically are designed to be run on a parallel machine with one process per core. If processes exhibit different computational load, either the code must be rewritten for load balancing, with negative side-effects on readability and maintainability, or the one-process-per-core philosophy leads to a low utilization of many processor cores. If several processes are mapped per core to increase CPU utilization, the load might still be unevenly distributed among the cores if the mapping is unaware of the process characteristics.

    Therefore, similarly to the MPI_Graph_create() function where the program gives hints on communication patterns so that MPI processes can be placed favorably, we propose a MPI_Load_create() function where the program supplies information on the relative loads of the MPI processes, such that processes can be favorably grouped and mapped onto processor cores. In order to account for scalability and restricted knowledge of individual MPI processes, we also propose an extension MPI_Dist_load_create() similar to MPI_Dist_graph_create(), where each individual MPI process only knows the loads of a subset of the MPI processes.

    We detail how to implement both variants on top of MPI, and provide experimental performance results both for synthetic and numeric example applications. The results indicate that load balancing is favorable in both cases.

  • 314.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Compiling for VLIW DSPs2010In: Handbook of signal processing systems / [ed] Shuvra S. Bhattacharyya, Ed F. Deprettere, Rainer Leupers, Jarmo Takala, New York: Springer, 2010, 1, p. 603-638Chapter in book (Refereed)
  • 315.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Compiling for VLIW DSPs2013In: Handbook of signal processing systems / [ed] Shuvra S. Bhattacharyya, Ed F. Deprettere, Rainer Leupers, Jarmo Takala, New York: Springer, 2013, 2, p. 1177-1214Chapter in book (Refereed)
    Abstract [en]

    This handbook, organized into four parts, provides the reader with a comprehensive and standalone overview of signal processing systems. It contains a comprehensive index for ease of use, and an extensive bibliography for further reading.

  • 316.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Fourth Swedish Workshop on Multi-Core Computing MCC-2011: November 23-25, 2011, Linköping University, Linköping, Sweden2011Conference proceedings (editor) (Other academic)
    Abstract [en]

    MCC-2011 covers a wide variety of topics, including programming for GPU-based systems, mobile multi-core based platforms, scalable concurrent data structures, memory hierarchies, auto-tuning, transactional memory and thread-level speculation, parallel programming models, scheduling and mapping, applications, and even teaching of multicore programming.

  • 317.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Programming Techniques for the Cell Processor2011In: it - Information Technology, ISSN 1611-2776, Vol. 53, no 2, p. 66-74Article in journal (Refereed)
    Abstract [en]

    Cell Broadband Engine is a heterogeneous multicore processor designed mainly for applications in scientific computing, graphics, and gaming with high performance requirements. We give an overview of its architecture, review some selected development tools and programming frameworks, and describe techniques for writing efficient programs for Cell.

  • 318.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Programming the Cell Processor2010In: Fundamentals of Multicore Software Development / [ed] Victor Pankratius, Ali-Reza Adl-Tabatabai, Walter Tichy, CRC Press, 2010, p. 155-198Chapter in book (Other academic)
  • 319.
    Kessler, Christoph
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Dastgeer, Usman
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Li, Lu
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Optimized Composition: Generating Efficient Code for Heterogeneous Systems from Multi-Variant Components, Skeletons and Containers2014In: Proc. First Workshop on Resource awareness and adaptivity in multi-core computing (Racing 2014), May 2014, Paderborn, Germany / [ed] F. Hannig and J. Teich, 2014, p. 43-48Conference paper (Refereed)
    Abstract [en]

    In this survey paper, we review recent work on frameworks for the high-level, portable programming of heterogeneous multi-/manycore systems (especially, GPU-based systems) using high-level constructs such as annotated user-level software components, skeletons (i.e., predefined generic components) and containers, and discuss the optimization problems that need to be considered in selecting among multiple implementation variants, generating code and providing runtime support for efficient execution on such systems.

  • 320.
    Kessler, Christoph
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Dastgeer, Usman
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Majeed, Mudassar
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Furmento, Nathalie
    University of Bordeaux, INRIA, Bordeaux, France.
    Thibault, Samuel
    University of Bordeaux, INRIA, Bordeaux, France.
    Namyst, Raymond
    University of Bordeaux, INRIA, Bordeaux, France.
    Benkner, Siegfried
    University of Vienna, Austria.
    Pllana, Sabri
    University of Vienna, Austria.
    Träff, Jesper
    Technical University of Vienna, Austria.
    Wimmer, Martin
    Technical University of Vienna, Austria.
    Leveraging PEPPHER Technology for Performance Portable Supercomputing2013In: High Performance Computing, Networking, Storage and Analysis (SCC), 2012 SC Companion, Salt Lake City, USA: IEEE conference proceedings, 2013, p. 1395-1396Conference paper (Other academic)
    Abstract [en]

    PEPPHER is a 3-year EU FP7 project that develops a novel approach and framework to enhance performance portability and programmability of heterogeneous multi-core systems. Its primary target is single-node heterogeneous systems, where several CPU cores are supported by accelerators such as GPUs. This poster briefly surveys the PEPPHER framework for single-node systems, and elaborates on the prospectives for leveraging the PEPPHER approach to generate performance-portable code for heterogeneous multi-node systems.

  • 321.
    Kessler, Christoph
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Dastgeer, Usman
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Thibault, Samuel
    INRIA / University of Bordeaux, France.
    Namyst, Raymond
    INRIA / University of Bordeaux, France.
    Richards, Andrew
    Codeplay Software Ltd., Edinburgh, UK.
    Dolinsky, Uwe
    Codeplay Software Ltd., Edinburgh, UK.
    Benkner, Siegfried
    University of Vienna, Austria.
    Träff, Jesper
    Technical University of Vienna, Austria.
    Pllana, Sabri
    University of Vienna, Austria.
    Programmability and Performance Portability Aspects of Heterogeneous Multi-/Manycore Systems2012Conference paper (Refereed)
    Abstract [en]

    We discuss three complementary approaches that can provide both portability and an increased level of abstraction for the programming of heterogeneous multicore systems. Together, these approaches also support performance portability, as currently investigated in the EU FP7 project PEPPHER. In particular, we consider (1) a library-based approach, here represented by the integration of the SkePU C++ skeleton programming library with the StarPU runtime system for dynamic scheduling and dynamic selection of suitable execution units for parallel tasks; (2) a language-based approach, here represented by the Offload-C++ high-level language extensions and Offload compiler to generate platform-specific code; and (3) a component-based approach, specifically the PEPPHER component system for annotating user-level application components with performance metadata, thereby preparing them for performance-aware composition. We discuss the strengths and weaknesses of these approaches and show how they could complement each other in an integrational programming framework for heterogeneous multicore systems.

  • 322.
    Kessler, Christoph
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Eitschberger, Patrick
    FernUniversität in Hagen, Germany.
    Keller, Jörg
    FernUniversität in Hagen, Germany.
    Energy-Efficient Static Scheduling of Streaming Task Collections with Malleable Tasks2013In: Proc. 25th PARS-Workshop, Gesellschaft für Informatik, 2013, p. 37-46Conference paper (Refereed)
    Abstract [en]

    We investigate the energy-efficiency of streaming task collections with parallelizable or malleable tasks on a manycore processor with frequency scaling. Streaming task collections differ from classical task sets in that all tasks are running concurrently, so that cores typically run several tasks that are scheduled round-robin on user level. A stream of data flows through the tasks and intermediate results are forwarded to other tasks like in a pipelined task graph. We first show the equivalence of task mapping for streaming task collections and normal task collections in the case of continuous frequency scaling, under reasonable assumptions for the user-level scheduler, if a makespan, i.e. a throughput requirement of the streaming application, is given and the energy consumed is to be minimized. We then show that in the case of discrete  frequency scaling, it might be necessary for processors to switch frequencies, and that idle times still can occur, in contrast to continuous frequency scaling. We formulate the mapping of (streaming) task collections on a manycore processor with discrete frequency levels as an integer linear program. Finally, we propose two heuristics to reduce energy consumption compared to the previous results by improved load balancing through the parallel execution of a parallelizable task. We evaluate the effects of the heuristics analytically and experimentally on the Intel SCC.

  • 323.
    Kessler, Christoph
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Hansson, Erik
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Flexible scheduling and thread allocation for synchronous parallel tasks2012In: ARCS-2012 Workshops / [ed] G. Mühl, J. Richling, A. Herkersdorf, Gesellschaft für Informatik , 2012, p. 517-528Conference paper (Refereed)
    Abstract [en]

    We describe a task model and dynamic scheduling and resource allocation mechanism for synchronous parallel tasks to be executed on SPMD-programmed synchronous shared memory MIMD parallel architectures with uniform, unit-time memory access and strict memory consistency, also known inthe literature as PRAMs (Parallel Random Access Machines). Our task model provides a two-tier programming model for PRAMs that flexibly combines SPMD and fork-join parallelism within the same application. It offers flexibility by dynamic scheduling and late resource binding while preserving the PRAM execution properties within each task, the only limitation being that the maximum number of threads that can be assigned to a task is limited to what the underlying architecture provides. In particular, our approach opens for automatic performance tuning at run-time by controlling the thread allocation for tasks based on run-time predictions.By a prototype implementation of a synchronous parallel task API in the SPMD-based PRAM language Fork and experimental evaluation with example programs on the SBPRAM simulator, we show that a realization of the task model on a SPMD-programmable PRAM machine is feasible with moderate runtimeoverhead per task.

  • 324.
    Kessler, Christoph
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Li, Lu
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Atalar, Aras
    Chalmers University of Technology, Gothenburg, Sweden.
    Dobre, Alin
    Movidius, Dublin, Ireland.
    XPDL: Extensible Platform Description Language to Support Energy Modeling and Optimization2015In: Proc. 44th International Conference on Parallel Processing Workshops, ICPP-EMS Embedded Multicore Systems, in conjunction with ICPP-2015, Beijing, 1-4 sep. 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 51-60Conference paper (Refereed)
    Abstract [en]

    We present XPDL, a modular, extensible platform description language for heterogeneous multicore systems and clusters. XPDL specifications provide platform metadata about hardware and installed system software that are relevant for the adaptive static and dynamic optimization of application programs and system settings for improved performance and energy efficiency. XPDL is based on XML and uses hyperlinks to create distributed libraries of platform metadata specifications. We also provide first components of a retarget able tool chain that browses and processes XPDL specifications, and generates driver code for micro benchmarking to bootstrap empirical performance and energy models at deployment time. A C++ based API enables convenient introspection of platform models, even at run-time, which allows for adaptive dynamic program optimizations such as tuned selection of implementation variants.

  • 325.
    Kessler, Christoph
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Melot, Nicolas
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Eitschberger, Patrick
    FernUniversität in Hagen, Germany.
    Keller, Jörg
    FernUniversität in Hagen, Germany.
    Crown Scheduling: Energy-Efficient Resource Allocation, Mapping and Discrete Frequency Scaling for Collections of Malleable Streaming Tasks2013In: Proceedings of the 23rd International Workshop on Power and Timing Modeling, Optimization and Simulation (PATMOS), 2013 / [ed] Jörg Henkel and Alex Yakovlev (eds.), IEEE Computer Society Digital Library, 2013, p. 215-222Conference paper (Refereed)
    Abstract [en]

    We investigate the problem of generating energy-optimal code for a collection of streaming tasks that include parallelizable or malleable tasks on a generic many-core processor with dynamic discrete frequency scaling. Streaming task collections differ from classical task sets in that all tasks are running concurrently, so that cores typically run several tasks that are scheduled round-robin at user level in a data driven way. A stream of data flows through the tasks and intermediate results are forwarded to other tasks like in a pipelined task graph. In this paper we present crown scheduling, a novel technique for the combined optimization of resource allocation, mapping and discrete voltage/frequency scaling for malleable streaming task sets in order to optimize energy efficiency given a throughput constraint. We present optimal off-line algorithms for separate and integrated crown scheduling based on integer linear programming (ILP). We also propose extensions for dynamic rescaling to automatically adapt a given crown schedule in situations where not all tasks are data ready. Our energy model considers both static idle power and dynamic power consumption of the processor cores. Our experimental evaluation of the ILP models for a generic manycore architecture shows that at least for small and medium sized task sets even the integrated variant of crown scheduling can be solved to optimality by a state-of-the-art ILP solver within a few seconds.

  • 326.
    Kessler, Christoph
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Pllana, SabriLinnaeus University, Växjö.
    Proceedings of the 2013 IEEE 6th International Workshop on Multi-/Many-core Computing Systems (MuCoCoS-2013)2013Conference proceedings (editor) (Refereed)
  • 327.
    Kessler, Martin
    et al.
    Linköping University.
    Hansson, Erik
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Åkesson, Daniel
    Linköping University, Department of Computer and Information Science. Linköping University, The Institute of Technology.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Exploiting Instruction Level Parallelism for REPLICA - A Configurable VLIW Architecture With Chained Functional Units2012In: : Volume II, Las Vegas, Nevada, USA: CSREA Press, 2012, p. 275-281Conference paper (Other academic)
    Abstract [en]

    In this paper we present a scheduling algorithm for VLIW architectures with chained functional units. We show how our algorithm can help speed up programs at the instruction level, for an architecture called REPLICA, a configurable emulated shared memory (CESM) architecture whose computation model is based on the PRAM model. Since our LLVM based compiler is parameterizable in the number of different functional units, read and write ports to register file etc. we can generate code for different REPLICA architectures that have different functional unit configurations. We show for a set of different configurations how our implementation can produce high quality code; and we argue that the high parametrization of the compiler makes it, together with the simulator, useful for hardware/software co-design.

  • 328.
    Kim, Jin-Hyun
    et al.
    INRIA/IRISA, France.
    Legay, Axel
    INRIA/IRISA, France.
    Traonouez, Louis-Marie
    INRIA/IRISA, France.
    Boudjadar, Abdeldjalil
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Nyman, Ulrik
    Aalborg University, Denmark.
    Larsen, Kim G.
    Aalborg University, Denmark.
    Lee, Insup
    University of Pennsylvania.
    Choi, Jin-Young
    Korea University, S. Korea.
    Optimizing the Resource Requirements of Hierarchical Scheduling Systems2016In: SIGBED Review, ISSN 1551-3688, Vol. 13, no 3, p. 41-48Article in journal (Other academic)
    Abstract [en]

    Compositional reasoning on hierarchical scheduling systems is a well-founded formal method that can construct schedulable and optimal system configurations in a compositional way. However, a compositional framework formulates the resource requirement of a component, called an interface, by assuming that a resource is always supplied by the parent components in the most pessimistic way. For this reason, the component interface demands more resources than the amount of resources that are really sufficient to satisfy sub-components. We provide two new supply bound functions which provides tighter bounds on the resource requirements of individual components. The tighter bounds are calculated by using more information about the scheduling system.

    We evaluate our new tighter bounds by using a model-based schedulability framework for hierarchical scheduling systems realized as Uppaal models. The timed models are checked using model checking tools Uppaal and Uppaal SMC, and we compare our results with the state of the art tool CARTS.

  • 329.
    Kinnander, Åke
    et al.
    Siemens Turbo Machinery AB, Finspång, Sweden.
    Sjölund, Martin
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Pop, Adrian
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Industrial Evaluation of Integrated Performance Analysis and Equation Model Debugging for Equation-Based Models2016In: Modeling, Identification and Control, ISSN 0332-7353, E-ISSN 1890-1328, Vol. 37, no 4, p. 225-236, article id 3Article in journal (Refereed)
    Abstract [en]

    The ease of use and the high abstraction level of equation-based object-oriented (EOO) languages such as Modelica has the drawback that performance problems and modeling errors are often hard to find. To address this problem, we have earlier developed advanced performance analysis and equation model debugging support in the OpenModelica tool. The aim of the work reported in this paper is to perform an independent investigation and evaluation of this equation model performance analysis and debugging methods and tool support on industrial models. The results turned out to be mainly positive. The integrated debugger and performance analyzer locates several kinds of errors such as division by zero, chattering, etc., and greatly facilitates finding the equations that take most of the execution time during simulation. It remains to further evaluate the performance profiler and debugger on even larger industrial models.

  • 330.
    Kircher, Katja
    et al.
    Linköping University, Department of Behavioural Sciences and Learning, Psychology. Linköping University, Faculty of Arts and Sciences. Swedish Natl Rd and Transport Res Inst VTI, Linkoping, Sweden.
    Ahlstrom, Christer
    Swedish Natl Rd and Transport Res Inst VTI, Linkoping, Sweden.
    Nylin, Magnus
    Linköping University, Department of Computer and Information Science. Linköping University, Faculty of Science & Engineering.
    Mengist, Alachew
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Tactical steering behaviour under irrevocable visual occlusion2018In: Transportation Research Part F: Traffic Psychology and Behaviour, ISSN 1369-8478, E-ISSN 1873-5517, Vol. 55, p. 67-77Article in journal (Refereed)
    Abstract [en]

    Objective: To investigate the extent of a drivers mental model with irrevocable visual occlusion and analysing the distance to crash. Background: Drivers have a mental model of the immediate surroundings which allows them to predict their own as well as others travel paths. To navigate safely through traffic, this mental model has to be updated frequently to remain valid. In between information sampling events, the mental model will become outdated over time, as the traffic system is dynamic. Method: A simulator study with 22 participants was conducted to investigate the information decay in the mental model. This was implemented by extending visual occlusion until the driver collided with another vehicle or ran off the road, thus providing an estimate of how long it takes until the mental model becomes obsolete. Results: An analysis of variance with the factors curve direction, curve radius and traffic showed that curve radius did not influence the distance to crash. Without traffic, drivers veered off the road sooner in right curves. Adding traffic eliminated this difference. Traffic ahead led to a shortened distance to crash. Compared to a tangential travel path from the current lateral position at the time of the occlusion, drivers crashed on average 2.6 times later than they would have, had they not had any mental model of the situation. Conclusions: The drivers mental representation of the future situation seems to include information on how to act, to alleviate deviations in yaw angle, including and considering the presence of other road users. (C) 2018 Elsevier Ltd. All rights reserved.

  • 331.
    Kosuch, Stefanie
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Approximability of the two-stage stochastic knapsack problem with discretely distributed weights2014In: Discrete Applied Mathematics, ISSN 0166-218X, E-ISSN 1872-6771, Vol. 165, p. 192-204Article in journal (Refereed)
    Abstract [en]

    In this paper the two-stage knapsack problem with random weights is studied under the aspect of approximability. We assume finite probability distributions for the weights and show that, unless P = NP, the so obtained problem cannot be approximated in polynomial time within a better ratio than K-1/2 (where K is the number of second-stage scenarios). We further study the special cases where in the second stage items can only be added or only be removed, but not both. Positive approximation results are given for three particular cases, namely linearly dependent first- and second-stage rewards, the polynomial scenario model and the case where the number of scenarios is assumed to be a constant. To the best of our knowledge, this is the first study of a two-stage knapsack problem under the aspect of approximability and the first time a non-approximability result has been proven for a stochastic knapsack problem of any kind.

  • 332.
    Krispinsson, Tobias
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Hybrid application development: A comparison between native Android application and Ionic 2 application2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis, the newly released framework Ionic 2, which claims to fix the problems cross platform frameworks has suffered from concerning bad performance and bad user experience, has been evaluated. The study has focused on the Android platform by comparing a native developed application to an Ionic 2 developed application. The comparison has been made on performance and user experience. As an extent, Ionic 2 are also compared to another evaluation study made for React Native, to see how the two frameworks differ, both performance wise and user experience wise. The native application performs better in all performance tests, even though the difference only was a few percent for memory usage and battery consumption. In the user tests, the result was of different nature. Some users did not notice any differences between the applications, whilst some had big concerns with how the application behaved. The overall conclusion is that Ionic still has some way to go to compete with native applications. If considering using Ionic 2, you need to be aware of the flaws it has. From the data gathered for this study, React Native is considered to be better than Ionic, but with new updates coming continuously, Ionic is improving every day.

  • 333.
    Kuhlmann, Marco
    et al.
    Linköping University, Department of Computer and Information Science, Human-Centered systems. Linköping University, Faculty of Science & Engineering.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Parsing to Noncrossing Dependency Graphs2015In: Transactions of the Association for Computational Linguistics, ISSN 2307-387X, Vol. 3, p. 559-570Article in journal (Refereed)
    Abstract [en]

    We study the generalization of maximum spanning tree dependency parsing to maximum acyclic subgraphs. Because the underlying optimization problem is intractable even under an arc-factored model, we consider the restriction to noncrossing dependency graphs. Our main contribution is a cubic-time exact inference algorithm for this class. We extend this algorithm into a practical parser and evaluate its performance on four linguistic data sets used in semantic dependency parsing. We also explore a generalization of our parsing framework to dependency graphs with pagenumber at most $k$ and show that the resulting optimization problem is NP-hard for k ≥ 2.

  • 334.
    Kuiper, Erik
    et al.
    Saab Aeronautical, Linkoping, Sweden .
    Nadjm-Tehrani, Simin
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Yuan, Di
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, The Institute of Technology.
    A framework for performance analysis of geographic delay-tolerant routing2012In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, no 184Article in journal (Refereed)
    Abstract [en]

    A major tool used for evaluating routing protocols in ad hoc and delay-tolerant networks is simulation. Whereas the results from simulations give good insights, they are limited to the specific scenario set-up that is used. If the scenario changes, new and often time-consuming simulations have to be run. Moreover, the simulation time in packet-level simulators with fairly realistic physical layer implementation, such as ns-2, generally grows rapidly in the number of nodes. This practically limits the number of nodes in a simulation, even if the limit can be extended by the use of simulation federations. Larger scenarios can also be facilitated by the use of more abstraction in the physical layer; abstractions that may impact the validity of the results. In this article, we present the forward-wait framework--a mathematical model describing the packet movements for opportunistic geographic delay-tolerant routing protocols. By describing packet movements as a sequence of alternating forwarding and waiting phases, the framework can accurately predict the routing performance. Key input parameters to the framework are random variables describing the forwarding and waiting phases. We show how the properties of the random variables can be derived, both via abstract modeling and small scale ns-2 simulation data. The model is then used to demonstrate the prediction capabilities of the framework in providing results that are close to the (much slower) packet-level simulations.

  • 335.
    Kurin, Erik
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Melin, Adam
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Data-driven test automation: augmenting GUI testing in a web application2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    For many companies today, it is highly valuable to collect and analyse data in order to support decision making and functions of various sorts. However, this kind of data-driven approach is seldomly applied to software testing and there is often a lack of verification that the testing performed is relevant to how the system under test is used. Therefore, the aim of this thesis is to investigate the possibility of introducing a data-driven approach to test automation by extracting user behaviour data and curating it to form input for testing.

    A prestudy was initially conducted in order to collect and assess different data sources for augmenting the testing. After suitable data sources were identified, the required data, including data about user activity in the system, was extracted. This data was then processed and three prototypes where built on top of this data. The first prototype augments the model-based testing by automatically creating models of the most common user behaviour by utilising data mining algorithms. The second prototype tests the most frequent occurring client actions. The last prototype visualises which features of the system are not covered by automated regression testing.

    The data extracted and analysed in this thesis facilitates the understanding of the behaviour of the users in the system under test. The three prototypes implemented with this data as their foundation can be used to assist other testing methods by visualising test coverage and executing regression tests.

  • 336.
    Kvarnström, Olle
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Static Code Analysis of C++ in LLVM2016Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    Just like the release of the Clang compiler, the advent of LLVM in the field of static code analysis already shows great promise. When given the task of covering rules not ideally covered by a commercial contender, the end result is not only overwhelmingly positive, the implementation time is only a fraction of what was initially expected. While LLVM’s support for sophisticated AST analysis is remarkable, being the main reason these positive results, it’s support for data flow analysis is not yet up to par. Despite this, as well as a lack of thorough documentation, LLVM should already be a strong rival for any commercial tool today.

  • 337.
    Lagerberg, Lina
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Skude, Tor
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    The impact of agile principles and practices on large-scale software development projects: A multiple-case study of two software development projects at Ericsson2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Agile software development methods are often advertised as a contrast to the traditional, plan-driven approach to software development. The reported and argued benefits on software quality, coordination, productivity and other areas are numerous. The base of empirical evidence to the claimed effects is however thin, and more empirical studies on the effects of agile software development methods in different contexts are needed, especially in large-scale, industrial settings.

    The purpose of the thesis was to study the impact of using agile principles and practices in large-scale software development projects at Ericsson and it was carried out as a multiple-case study of two projects. One of the projects had implemented a limited number of agile software development practices and was largely plan-driven, while the other project had fully adapted its organization and product design for agile software development. Propositions of possible effects of the use of agile principles and practices in the two projects were generated by a literature review. Empirical data was then collected from online surveys of project members, internal documents, personal contact with key project members and a collection of metrics, to study the presence of the proposed effects.

    The study was focused on eight different areas: internal software documentation, knowledge sharing, project visibility, pressure and stress, productivity, software quality and project success rate.

    Agile principles and practices were found to:

    • Lead to a more balanced use of internal software documentation, when supported by sound documentation policies.
    • Contribute to knowledge sharing.
    • Increase project members’ visibility of the status of other teams and the entire project.
    • Increase coordination effectiveness and reducing the need for other types of coordination mechanisms.
    • Increase productivity.
    • Possibly increase software quality.

    Additionally, the study showed that internal software documentation is important also in agile software development projects, and cannot fully be replaced with face-to-face communication. Further, it was clear that it’s possible to make a partial implementation of agile principles and practices, and still receive a positive impact. Finally, the study showed that it’s feasible to implement agile principles and practices in large-scale software development. It therefore contributes to understanding the effects of agile software development in different contexts.

  • 338.
    Lagerberg, Lina
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Skude, Tor
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Sandahl, Kristian
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Emanuelsson, Pär
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Ståhl, Daniel
    Ericsson AB, Linköping, Sweden.
    The impact of agile principles and practices on large-scale software development projects: A multiple-case study of two projects at Ericsson2013In: Empirical Software Engineering and Measurement, 2013, Los Alamitos: IEEE , 2013, p. 348-356Conference paper (Refereed)
    Abstract [en]

    BACKGROUND: Agile software development methods have a number of reported benefits on productivity, project visibility, software quality and other areas. There are also negative effects reported. However, the base of empirical evidence to the claimed effects needs more empirical studies. AIM: The purpose of the research was to contribute with empirical evidence on the impact of using agile principles and practices in large-scale, industrial software development. Research was focused on impacts within seven areas: Internal software documentation, Knowledge sharing, Project visibility, Pressure and stress, Coordination effectiveness, and Productivity. METHOD: Research was carried out as a multiple-case study on two contemporary, large-scale software development projects with different levels of agile adoption at Ericsson. Empirical data was collected through a survey of project members. RESULTS AND CONCLUSIONS: Intentional implementation of agile principles and practices were found to: correlate with a more balanced use of internal software documentation, contribute to knowledge sharing, correlate with increased project visibility and coordination effectiveness, reduce the need for other types of coordination mechanisms, and possibly increase productivity. No correlation with increase in pressure and stress were found.

  • 339.
    Lagerkvist, Vicktor
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Wahlström, Magnus
    Department of Computer Science, Royal Holloway, University of London, Great Britain.
    Zanuttini, Bruno
    GREYC, Normandie Université, UNICAEN, CNRS, ENSICAEN, Franc.
    Bounded Bases of Strong Partial Clones2015In: Multiple-Valued Logic (ISMVL), 2015 IEEE International Symposium on, IEEE , 2015, p. 189-194Conference paper (Refereed)
    Abstract [en]

    Partial clone theory has successfully been applied to study the complexity of the constraint satisfaction problem parameterized by a set of relations (CSP(G)). Lagerkvist & Wahlstroï¿œm (ISMVL 2014) however shows that the partial polymorphisms of G (?P?I(G)) cannot be finitely generated for finite, Boolean G if CSP(G) is NP-hard (assuming P?NP). In this paper we consider stronger closure operators than functional composition which can generate ?P?I(G) from a finite set of partial functions, a bounded base. Determining bounded bases for finite languages provides a complete characterization of their partial polymorphisms and we provide such bases for k-SAT and 1-in-k-SAT.

  • 340.
    Lagerkvist, Victor
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Precise Upper and Lower Bounds for the Monotone Constraint Satisfaction Problem2015In: MATHEMATICAL FOUNDATIONS OF COMPUTER SCIENCE 2015, PT I, SPRINGER-VERLAG BERLIN , 2015, Vol. 9234, p. 357-368Conference paper (Refereed)
    Abstract [en]

    The monotone constraint satisfaction problem (MCSP) is the problem of, given an existentially quantified positive formula, decide whether this formula has a model. This problem is a natural generalization of the constraint satisfaction problem, which can be seen as the problem of determining whether a conjunctive formula has a model. In this paper we study the worst-case time complexity, measured with respect to the number of variables, n, of the MCSP problem parameterized by a constraint language Gamma (MCSP(Gamma)). We prove that the complexity of the NP-complete MCSP(G) problems on a given finite domain D falls into exactly vertical bar D vertical bar-1 cases and ranges from O(2(n)) to O(vertical bar D vertical bar(n)). We give strong lower bounds and prove that MCSP(G), for any constraint language Gamma over any finite domain, is solvable in O(vertical bar Dvertical bar n) time, where D- is the domain of the core of Gamma, but not solvable in O(vertical bar Dvertical bar(delta n)) time for any delta < 1, unless the strong exponential-time hypothesis fails. Hence, we obtain a complete understanding of the worst-case time complexity of MCSP(Gamma) for constraint languages over arbitrary finite domains.

  • 341.
    Lagerkvist, Victor
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Strong Partial Clones and the Complexity of Constraint Satisfaction Problems: Limitations and Applications2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    In this thesis we study the worst-case time complexity of the constraint satisfaction problem parameterized by a constraint language (CSP(S)), which is the problem of determining whether a conjunctive formula over S has a model. To study the complexity of CSP(S) we borrow methods from universal algebra. In particular, we consider algebras of partial functions, called strong partial clones. This algebraic approach allows us to obtain a more nuanced view of the complexity CSP(S) than possible with algebras of total functions, clones.

    The results of this thesis is split into two main parts. In the first part we investigate properties of strong partial clones, beginning with a classification of weak bases for all Boolean relational clones. Weak bases are constraint languages where the corresponding strong partial clones in a certain sense are extraordinarily large, and they provide a rich amount of information regarding the complexity of the corresponding CSP problems. We then proceed by classifying the Boolean relational clones according to whether it is possible to represent every relation by a conjunctive, logical formula over the weak base without needing more than a polynomial number of existentially quantified variables. A relational clone satisfying this condition is called polynomially closed and we show that this property has a close relationship with the concept of few subpowers. Using this classification we prove that a strong partial clone is of infinite order if (1) the total functions in the strong partial clone are essentially unary and (2) the corresponding constraint language is finite. Despite this, we prove that these strong partial clones can be succinctly represented with finite sets of partial functions, bounded bases, by considering stronger notions of closure than functional composition.

    In the second part of this thesis we apply the theory developed in the first part. We begin by studying the complexity of CSP(S) where S is a Boolean constraint language, the generalised satisfiability problem (SAT(S)). Using weak bases we prove that there exists a relation R such that SAT({R}) is the easiest NP-complete SAT(S) problem. We rule out the possibility that SAT({R}) is solvable in subexponential time unless a well-known complexity theoretical conjecture, the exponential-time hypothesis, (ETH) is false. We then proceed to study the computational complexity of two optimisation variants of the SAT(S) problem: the maximum ones problem over a Boolean constraint language S (MAX-ONES(S)) and the valued constraint satisfaction problem over a set of Boolean cost functions Δ (VCSP(Δ)). For MAX-ONES(S) we use partial clone theory and prove that MAX-ONES({R}) is the easiest NP-complete MAX-ONES(S) problem. These algebraic techniques do not work for VCSP(Δ), however, where we instead use multimorphisms to prove that MAX-CUT is the easiest NP-complete Boolean VCSP(Δ) problem. Similar to the case of SAT(S) we then rule out the possibility of subexponential algorithms for these problems, unless the ETH is false.

  • 342.
    Lagerkvist, Victor
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Weak bases of Boolean co-clones2014In: Information Processing Letters, ISSN 0020-0190, E-ISSN 1872-6119, Vol. 114, no 9, p. 462-468Article in journal (Refereed)
    Abstract [en]

    Universal algebra has proven to be a useful tool in the study of constraint satisfaction problems (CSP) since the complexity, up to logspace reductions, is determined by the clone of the constraint language. But two CSPs corresponding to the same clone may still differ substantially with respect to worst-case time complexity, which makes clones ill-suited when comparing running times of CSP problems. In this article we instead consider an algebra where each clone splits into an interval of strong partial clones such that a strong partial clone corresponds to the CSPs that are solvable within the same O(c(n)) bound. We investigate these intervals and give relational descriptions, weak bases; of the largest elements. They have a highly regular form and are in many cases easily relatable to the smallest members in the intervals, which suggests that the lattice of strong partial clones has a simpler structure than the lattice of partial clones.

  • 343.
    Lagerkvist, Victor
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Wahlström, Magnus
    Linköping University, Department of Computer and Information Science, TCSLAB - Theoretical Computer Science Laboratory. Linköping University, The Institute of Technology. Univ London, Dept Comp Sci, London WC1E 7HU, England.
    Polynomially Closed Co-clones2014In: 2014 IEEE 44TH INTERNATIONAL SYMPOSIUM ON MULTIPLE-VALUED LOGIC (ISMVL 2014), IEEE Computer Society, 2014, p. 85-90Conference paper (Refereed)
    Abstract [en]

    Two well-studied closure operators for relations are based on primitive positive (p.p.) definitions and quantifier free p.p. definitions. The latter do however have limited expressiveness and the corresponding lattice of strong partial clones is uncountable. We consider implementations allowing polynomially many existentially quantified variables and obtain a dichotomy for co-clones where such implementations are enough to implement any relation and prove (1) that all remaining coclones contain relations requiring a superpolynomial amount of quantified variables and (2) that the strong partial clones corresponding to two of these co-clones are of infinite order whenever the set of invariant relations can be finitely generated.

  • 344.
    Lagerkvist, Victor
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Wahlström, Magnus
    Royal Holloway University of London, England.
    The power of primitive positive definitions with polynomially many variables2017In: Journal of logic and computation (Print), ISSN 0955-792X, E-ISSN 1465-363X, Vol. 27, no 5, p. 1465-1488Article in journal (Refereed)
    Abstract [en]

    Two well-studied closure operators for relations are based on existentially quantified conjunctive formulas, primitive positive (p.p.) definitions, and primitive positive formulas without existential quantification, quantifier-free primitive positive definitions (q.f.p.p.) definitions. Sets of relations closed under p.p. definitions are known as co-clones and sets of relations closed under q.f.p.p. definitions as weak partial co-clones. The latter do however have limited expressivity, and the corresponding lattice of strong partial clones is of uncountably infinite cardinality even for the Boolean domain. Hence, it is reasonable to consider the expressiveness of p.p. definitions where only a small number of existentially quantified variables are allowed. In this article, we consider p.p. definitions allowing only polynomially many existentially quantified variables, and say that a co-clone closed under such definitions is polynomially closed, and otherwise superpolynomially closed. We investigate properties of polynomially closed co-clones and prove that if the corresponding clone contains a k-ary near-unanimity operation for k amp;gt;= 3, then the co-clone is polynomially closed, and if the clone does not contain a k-edge operation for any k amp;gt;= 2, then the co-clone is superpolynomially closed. For the Boolean domain we strengthen these results and prove a complete dichotomy theorem separating polynomially closed co-clones from superpolynomially closed co-clones. Using these results, we then proceed to investigate properties of strong partial clones corresponding to superpolynomially closed co-clones. We prove that if Gamma is a finite set of relations over an arbitrary finite domain such that the clone corresponding to Gamma is essentially unary, then the strong partial clone corresponding to Gamma is of infinite order and cannot be generated by a finite set of partial functions.

  • 345.
    Lambrix, Patrick
    et al.
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Göthe Lundgren, Maud
    Linköping University, Department of Science and Technology, Communications and Transport Systems. Linköping University, Faculty of Science & Engineering.
    Kamkar, Mariam
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Computer science as an integrated part of engineering education1997In: Proceedings of the ACM SIGCSE/SIGCUE Conference on Integrating Technology into Computer Science Education, 1997, p. 151-Conference paper (Refereed)
  • 346.
    Lambrix, Patrick
    et al.
    Linköping University, Department of Computer and Information Science, Database and information techniques. Linköping University, Faculty of Science & Engineering.
    Kamkar, Mariam
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Computer Science as an Integrated Part of Engineering Education1998In: Proceedings of the Third ACM SIGCSE/SIGCUE Conference on Integrating Technology into Computer Science Education, 1998, p. 153-156Conference paper (Refereed)
    Abstract [en]

    The Information Technology curriculum at Linköping University has as goal to form engineers with an integrated view of engineering. The teaching philosophy in this curriculum is Problem-Based Learning. The education in each term is organised in a number of themes where topics from different disciplines are integrated. We describe a particular term in the Information Technology curriculum as an example of the approach and the integration of computer science teaching with the teaching of other disciplines. An important advantage of the approach is that the students discover interactions between different disciplines and view the different topics as naturally connected. Also, the students seem to have a better understanding of the topics and are better motivated. Further, they obtain improved communication and co-operation skills. Another advantage is that the approach is appreciated by our female students, which has led to a higher percentage of female students in this curriculum compared to our other computer science curricula.

  • 347.
    Larsson, Adam
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Prestandautvärdering av koppling mellan C#.NET och Pitch Runtime Infrastructure2014Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    Denna rapport dokumenterar arbetet med att utreda hur C# och Pitch RTI fungerar tillsammans, och vilka prestandaeffekter som resulterar av denna koppling. Motiveringen kommer från att kunder till företaget Pitch har efterfrågat stöd för C# som programmeringsspråk när de använder Pitch RTI. Metoden gick ut på att successivt lära sig använda de tekniker som finns tillgängliga, för att sedan implementera lösningar på hur kopplingen ska ske. Resultaten visar hur övergången går till och prestandan som uppnåddes med hjälp av indexnotation. Tekniken IKVM hade högre prestandaindex och gick snabbare att komma igång med jämfört med tekniken C++/CLI. Men C++/CLI passar bättre ur ett distributionsperspektiv. Slutsatsen blev att Pitch som företag med hjälp av denna rapport är bättre förberett på framtida utredningar och implementationer som skulle använda de utvärderade teknikerna.

  • 348.
    Larsson, Christian
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Application development for automated positioning of 3D-representations of a modularized product2013Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    This thesis presents an application that performs positioning of modules automatically based on given data for every module, and the development of it. The basis of the application is from a previous thesis code. On top of that code, more features and error handling has been added, as well as fixes for various bugs. A stress test has been performed and further development possibilities are being presented.

    The thesis work was carried out at Toyota Material Handling Mjölby (TMH) and was made in parallel with another thesis by Fredrik Holden who was generating data for the application. For a complete understanding of the theory and background, please also read Holden’s thesis report “Development of method for automated positioning of 3D-representations of a modularized product”, as well as the former thesis  ”Analysis for Automated Positioning of 3D-representation of a Modularized product””.

  • 349.
    Laurentz, Henrik
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Feasibility of using network support data to predict risk level of trouble tickets2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Internet Service Providers gather vast amounts of data in the form of trouble tickets created from connectivity related issues. This data is often stored and seldom used for proactive purposes. This thesis explores the feasibility of finding correlations in network support data through the use of data mining activities. Correlations such as these could be used for improving troubleshooting or staffing related activities. The approach uses the data mining methodology CRISP-DM to investigate typical data mining operations from the perspective of a Network Operation Center. The results show that correlations between the solving time and other ticket related attributes do exist and that support data could be used for the activities mentioned. The results also show that it exists a lot of room for improvement when it comes to data mining activities in network support data.

  • 350.
    Lewin, Marcus
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Grant, Harald
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Klientbaserad GeoTIFF-rendering2017Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    När en användare idag efterfrågar rendering av en kartvy i en applikation behöver en server först rendera en bild utifrån given geografisk data och därefter skicka bilden till klientens mobila enhet. Detta kan resultera i höga responstider, speciellt för användare som befinner sig i områden med bristfällig täckning. I denna studie utvärderas en alternativ lösning där rendering istället sker direkt på klientens enhet. En prototyp av en mobil kartapplikation med stöd för lokal rendering av geografisk rådata utvecklas och utvärderas utefter en konstant för acceptabel fördröjning vid visualisering av information. Resultatet av testerna visar att prototypens prestanda är beroende av mängden information som ska visas. För högre zoomnivåer ger prototypen ett tillfredsställande resultat, men vidare åtgärder krävs för de lägre nivåerna. De främsta utmaningarna vid utvecklingen av applikationen redovisas och förbättringsförslag för fortsatt utveckling framförs.

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