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  • 101.
    Bodirsky, Manuel
    et al.
    Ecole Polytechnique, Palaiseau, France.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    von Oertzen, Timo
    University of Virginia, USA.
    Horn versus Full First-order: Complexity Dichotomies in Algebraic Constraint Satisfaction2012In: Journal of logic and computation (Print), ISSN 0955-792X, E-ISSN 1465-363X, Vol. 22, no 3, 643-660 p.Article in journal (Refereed)
    Abstract [en]

    We study techniques for deciding the computational complexity of infinite-domain constraint satisfaction problems. For certain fundamental algebraic structures Delta, we prove definability dichotomy theorems of the following form: for every first-order expansion Gamma of Delta, either Gamma has a quantifier-free Horn definition in Delta, or there is an element d of Gamma such that all non-empty relations in Gamma contain a tuple of the form (d,...,d), or all relations with a first-order definition in Delta have a primitive positive definition in Gamma. The results imply that several families of constraint satisfaction problems exhibit a complexity dichotomy: the problems are in P or NP-hard, depending on the choice of the allowed relations. As concrete examples, we investigate fundamental algebraic constraint satisfaction problems. The first class consists of all first-order expansions of (Q;+). The second class is the affine variant of the first class. In both cases, we obtain full dichotomies by utilising our general methods.

  • 102.
    Bodirsky, Manuel
    et al.
    Ecole Polytechnique, Palaiseau, France.
    Wrona, Michal
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Equivalence Constraints2012Conference paper (Other academic)
    Abstract [en]

    The following result for finite structures Gamma has been conjectured to hold for all countably infinite omega-categorical structures Gamma: either the model-complete core Delta of Gamma has an expansion by finitely many constants such that the pseudovariety generated by its polymorphism algebra contains a two-element algebra all of whose operations are projections, or there is a homomorphism f from Delta^k to Delta, for some finite k, and an automorphism alpha of Delta satisfying f(x1,...,xk) = alpha(f(x2,...,xk,x1)). This conjecture has been confirmed for all infinite structures Gamma that have a first-order definition over (Q;<), and for all structures that are definable over the random graph. In this paper, we verify the conjecture for all structures that are definable over an equivalence relation with a countably infinite number of countably infinite classes. Our result implies a complexity dichotomy (into NP-complete and P) for a family of constraint satisfaction problems (CSPs) which we call equivalence constraint satisfaction problems. The classification for equivalence CSPs can also be seen as a first step towards a classification of the CSPs for all relational structures that are first-order definable over Allen's interval algebra, a well-known constraint calculus in temporal reasoning.

  • 103.
    Boije, Niklas
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Borg, Kristoffer
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Semi-automatic code-to-code transformer for Java: Transformation of library calls2016Independent thesis Advanced level (degree of Master (Two Years)), 300 HE creditsStudent thesis
    Abstract [en]

    Having the ability to perform large automatic software changes in a code base gives new possibilities for software restructuring and cost savings. The possibility of replacing software libraries in a semi-automatic way has been studied. String metrics are used to find equivalents between two libraries by looking at class- and method names. Rules based on the equivalents are then used to describe how to apply the transformation to the code base. Using the abstract syntax tree, locations for replacements are found and transformations are performed. After the transformations have been performed, an evaluation of the saved effort of doing the replacement automatically versus manually is made. It shows that a large part of the cost can be saved. An additional evaluation calculating the maintenance cost saved annually by changing libraries is also performed in order to prove the claim that an exchange can reduce the annual cost for the project.

  • 104.
    Bolinder, Richard
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Atmospheric Radiation Effects Study on Avionics: An Analysis of NFF Errors2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    No fault found (NFF) errors, i.e. errors which origin has not been established, irregularly occur in electronic devices. The actual cause of such errors varies but one, possibly more prominent, source for these soft errors is atmospheric radiation.

    The overarching aim of this thesis is to demonstrate: 1) the importance of keeping the atmospheric radiation environment in mind when designing robust airborne systems, 2) how to take this environment into consideration when applying mitigation techniques which may drastically reduce the risk of SEEs (Single Event Effects) which can cause NFF errors. To achieve these goals, Part 1 of this thesis describes how cosmic rays affect electronics (i.e. what kind of errors may be induced), which types of devices are susceptible to radiation, and why this subject is of extra importance for airborne systems. In addition, soft error mitigation techniques, which may be applied at different design levels to reduce the soft error rate (SER) or the impact of soft errors, are also presented.

    The aim is further corroborated by Part 2. Five subsystems of a modern aircraft are studied and real examples of failures potentially induced by atmospheric radiation are presented. For each of the five systems, all errors that have been reported for these (in the past few years) have been studied, and the number of errors found to be potentially induced by cosmic radiation has been listed and compared to number of expected soft errors based on calculations and previous experimental tests.

  • 105.
    Bordoloi, Unmesh D.
    et al.
    Linköping University, Department of Computer and Information Science, ESLAB - Embedded Systems Laboratory. Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Aminifar, Amir
    Linköping University, Department of Computer and Information Science, ESLAB - Embedded Systems Laboratory. Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Eles, Petru
    Linköping University, Department of Computer and Information Science, ESLAB - Embedded Systems Laboratory. Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Peng, Zebo
    Linköping University, Department of Computer and Information Science, ESLAB - Embedded Systems Laboratory. Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Schedulability Analysis of Ethernet AVB Switches2014In: 20th IEEE International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA 2014), Chongqing, China, Aug. 20-22, 2014., IEEE Computer Society, 2014Conference paper (Refereed)
    Abstract [en]

    Ethernet AVB is being actively considered by the automotive industry as a candidate for in-vehicle communication backbone. However, several questions pertaining to schedulability of hard real-time messages transmitted via such a switch remain unanswered. In this paper, we attempt to fill this void. We derive equations to perform worst-case response time analysis on Ethernet AVB switches by considering its credit-based shaping algorithm. Also, we propose several approaches to reduce the pessimism in the analysis to provide tighter bounds.

  • 106.
    Bordoloi, Unmesh D.
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Tanasa, Bogdan
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Eles, Petru
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Peng, Zebo
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    On the Timing Analysis of the Dynamic Segment of FlexRay2012In: International Symposium on Industrial Embedded Systems (SIES 2012), Karlsruhe, Germany, June 20-22, 2012., 2012Conference paper (Other academic)
    Abstract [en]

    FlexRay, developed by a consortium of over hundred automotive companies, is a real-time communication protocol for automotive networks. A communication cycle in FlexRay consists of an event-triggered component known as the dynamic (DYN) segment, apart from a time-triggered segment. Predicting the worst-case response time of messages transmitted on the DYN segment is a difficult problem. This is because a set of complex rules, apart from the priorities of the messages, govern the DYN segment protocol. In this paper, we survey techniques for the timing analysis of the DYN segment. We discuss the challenges associated with the timing analysis of the FlexRay protocol, the proposed techniques and their limitations.

  • 107.
    Bordoloi, Unmesh D.
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Tanasa, Bogdan
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Tahoori, Mehdi B.
    Institute of Computer Science & Engineering (ITEC), Karlsruhe Institute of Technology (KIT), Germany.
    Eles, Petru
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Peng, Zebo
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Shazli, Syed Z.
    Northeastern University, USA.
    Chakraborty, Samarjit
    Technical University of Munich, Germany.
    Reliability-Aware Instruction Set Customization for ASIPs with Hardened Logic2012In: International Conference on Embedded and Real-Time Computing Systems and Applications (RTCSA 2012), Seoul, Korea, August 19-22, 2012., 2012Conference paper (Refereed)
    Abstract [en]

    Application-specific instruction-set processors (ASIPs) allow the designer to extend the instruction set of the base processor with selected custom instructions to tailor-fit the application.In this paper, with the help of a motivational example, we first demonstrate that different custom instructions are vulnerable to faults with varying probabilities. This shows that by ignoring the vulnerability to faults, traditional methods of instruction set customization can provide no guarantees on the reliability of the system. Apart from such inherent disparity in error vulnerability across custom instructions, each custom instruction can have multiple implementation choices corresponding to varying hardened levels. Hardening reduces the vulnerability to errors but this comes at the overhead of area costs and reduced performance gain. In this paper, we propose a framework to select custom instructions and their respective hardening levels such that reliability is optimized while the performance gain is satisfied and area costs are met as well. Our framework is based on a novel analytical method to compute the overall system reliability based on the probability of failure of individual instructions. Wide range of experiments that were conducted illustrate how our tool navigates the design space to reveal interesting tradeoffs.

  • 108.
    Bordoloi, Unmesh
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Samii, Soheil
    Linköping University, Department of Computer and Information Science, ESLAB - Embedded Systems Laboratory. Linköping University, The Institute of Technology.
    The Frame Packing Problem for CAN-FD2014In: Real-Time Systems Symposium (RTSS 2014), Rome, Italy, Dec. 2-5, 2014., IEEE Press, 2014, 284-293 p.Conference paper (Refereed)
    Abstract [en]

    CAN with flexible data rate (CAN-FD) allows transmission of larger payloads compared to standard CAN. However, efficient utilization of CAN-FD bandwidth space calls for a systematic strategy. The challenge arises from the nature of the frame sizes stipulated by CAN-FD as well as the heterogeneity of the periods of the messages and the signals. In this paper, we formulate a frame packing problem for CAN-FD with the optimization objective of bandwidth utilization while meeting temporal constraints. As part of the solution, first, we propose a formula to compute the best-case and the worst-case transmission times of the CAN-FD frames. Thereafter, we propose a framework that solves the optimization problem in pseudo-polynomial time. Experiments show the gains achieved by our framework. The results also show that, when applied to standard CAN, our heuristic provides improved results over existing techniques.

  • 109.
    Borek, Paul
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    SMT Aided Test Case Generation For Constrained Feature Models2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With the development of highly configurable and large software, a new challenge has to be addressed, when it comes to software testing. While traditional testing approaches might still apply and succeed in achieving a better quality of service, the high degree of customizable parts of such a system implies the mentioned testing activities on different configurations. If a formal notion is used to express the allowed configurations of a system, one might think of generating such configurations in an automated fashion. However, if there are constraints involved, traditional model-based test-case generation might cause problems to achieve a desired coherency. An idea is, to use those constraints to generate test-cases and to achieve coherency at the same time. Satisfiability modulo theories (SMT) has been an emerging field in current theoretical computer science and developed decision procedures to treat various theoretical fragments in a specific manner. The goal of this thesis is, to look at a translation mechanism from an expression language for constraints into SAT modulo theories and involve this technique into a test-case generation process. Furthermore, the balance between the generation of coherent test-cases as well as the problem-specific purposes of such test-cases is investigated.

  • 110.
    Boudjadar, Abdeldjalil
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    David, Alexandre
    Aalborg University, Denmark.
    Hyun Kim, Jin
    INRIA IRISA, France.
    Larsen, Kim G.
    Aalborg University, Denmark.
    Mikucionis, Marius
    Aalborg University, Denmark.
    Nyman, Ulrik
    Aalborg University, Denmark.
    Skou, Arne
    Aalborg University, Denmark.
    A reconfigurable framework for compositional schedulability and power analysis of hierarchical scheduling systems with frequency scaling2015In: Science of Computer Programming, ISSN 0167-6423, E-ISSN 1872-7964, Vol. 113, 236-260 p.Article in journal (Refereed)
    Abstract [en]

    This paper presents a compositional framework for the modeling and analysis of hierarchical scheduling systems. We consider both schedulability and energy consumption of individual components, while analyzing a single core setting with a voltage frequency scaling CPU. According to the CPU frequency scaling, each task has a set of different execution times. Thus, the energy consumption of the whole system varies from one execution to another. We analyze each component individually by checking the feasibility of its workload against both the CPU availability and energy consumption constraints of such a component. Our periodic task model considers both static and dynamic priorities together with preemptive and non-preemptive behaviors. The models are realized using different forms of Hybrid Automata, all of which are analyzed using variants of UPPAAL. The CPU frequencies, task behavior and scheduling policies used in each component are some of the reconfigurable parameters of the system. Finally, we demonstrate the applicability and scalability of our framework by analyzing the schedulability and power consumption of an avionics system. (C) 2015 Elsevier B.V. All rights reserved.

  • 111.
    Boudjadar, Abdeldjalil
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    David, Alexandre
    Computer Science, Aalborg University, Denmark.
    Hyun Kim, Jin
    Computer Science, Aalborg University, Denmark.
    Larsen, Kim G.
    Computer Science, Aalborg University, Denmark.
    Mikučionis, Marius
    Computer Science, Aalborg University, Denmark.
    Nyman, Ulrik
    Computer Science, Aalborg University, Denmark.
    Skou, Arne
    Computer Science, Aalborg University, Denmark.
    Statistical and exact schedulability analysis of hierarchical scheduling systems2016In: Science of Computer Programming, ISSN 0167-6423, E-ISSN 1872-7964, Vol. 7, 103-130 p.Article in journal (Refereed)
    Abstract [en]

    This paper contains two contributions: 1) A development methodology involving two techniques to enhance the resource utilization and 2) a new generic multi-core resource model for hierarchical scheduling systems.

    As the first contribution, we propose a two-stage development methodology relying on the adjustment of timing attributes in the detailed models during the design stage. We use a lightweight method (statistical model checking) for design exploration, easily assuring high confidence in the correctness of the models. Once a satisfactory design has been found, it can be proved schedulable using the computation costly method (symbolic model checking). In order to analyze a hierarchical scheduling system compositionally, we introduce the notion of a stochastic supplier modeling the supply of resources from each component to its child components in the hierarchy. We specifically investigate two different techniques to widen the set of provably schedulable systems: 1) a new supplier model; 2) restricting the potential task offsets.

    We also provide a way to estimate the minimum resource supply (budget) that a component is required to provide. In contrast to analytical methods, we prove non-schedulable cases via concrete counterexamples. By having richer and more detailed scheduling models this framework, has the potential to prove the schedulability of more systems.

    As the second contribution, we introduce a generic resource model for multi-core hierarchical scheduling systems, and show how it can be instantiated for classical resource models: Periodic Resource Models (PRM) and Explicit Deadline Periodic (EDP) resource models. The generic multi-core resource model is presented in the context of a compositional model-based approach for schedulability analysis of hierarchical scheduling systems.

    The multi-core framework presented in this paper is an extension of the single-core framework used for the analysis in the rest of the paper.

  • 112.
    Boudjadar, Jalil
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Hyun Kin, Jin
    University of Pennsylvania, USA.
    Nadjm-Tehrani, Simin
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Performance-aware Scheduling of Multicore Time-critical Systems2016In: / [ed] IEEE, IEEE, 2016, 105-114 p.Conference paper (Refereed)
    Abstract [en]

    Despite attractiveness of multicore processors for embedded systems, the potential performance gains need to be studied in the context of real-time task scheduling and memory interference. This paper explores performance-aware schedula-bility of multicore systems by evaluating the performance when changing scheduling policies (as design parameters). The modelbased framework we build enables analyzing the performance of multicore time-critical systems using processor-centric and memory-centric scheduling policies. The system architecture we consider consists of a set of cores with a local cache and sharing the cache level L2 and main memory (DRAM). The metrics we use to compare the performance achieved by different configurations of a system are: 1) utilization of the cores; and 2) the maximum delay per access request to shared cache and DRAM. Our framework, realized using UPPAAL, can be viewed as an engineering tool to be used during design stages to identify the scheduling policies that provide better performance for a given system while maintaining system schedulability. As a proof of concept, we analyze and compare 2 different cases studies.

  • 113.
    Boudjadar, Jalil
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Madzar, Boris
    Queen's University Canada.
    Dingel, Juergen
    Queen's University Canada.
    Fuhrman, Thomas
    General Motors Co.
    S, Ramesh
    General Motors Co.
    Formal Analysis of Predictable Data Flow in Fault-Tolerant Multicore Systems2016Conference paper (Refereed)
    Abstract [en]

    The need to integrate large and complex functions into today’s vehicle electronic control systems requires high performance computing platforms, while at the same time the manufacturers try to reduce cost, power consumption and ensure safety. Traditionally, safety isolation and fault containment of software tasks have been achieved by either physically or temporally segregating them. This approach is reliable but inefficient in terms of processor utilization. Dynamic approaches that achieve better utilization without sacrificing safety isolation and fault containment appear to be of increasing interest. One of these approaches relies on predictable data flow introduced in PharOS and Giotto. In this paper, we extend the work on leveraging predictable data flow by addressing the problem of how the predictability of data flow can be proved formally for mixed criticality systems that run on multicore platforms and are subject to failures. We consider dynamic tasks where the timing attributes vary from one period to another. Our setting also allows for sporadic deadline overruns and accounts for criticality during fault handling. A user interface was created to allow automatic generation of the models as well as visualization of the analysis results, whereas predictability is verified using the Spin model checker

  • 114.
    Boudjadar, Jalil
    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.
    Schedulability and Memory Interference Analysis of Multicore Preemptive Real-time Systems2017In: 8th ACM/SPEC International Conference on Performance Engineering. L’Aquila Italy, April 2017, 2017Conference paper (Refereed)
    Abstract [en]

    Today's embedded systems demand increasing computingpower to accommodate the ever-growing software functionality.Automotive and avionic systems aim to leverage thehigh performance capabilities of multicore platforms, but arefaced with challenges with respect to temporal predictability.Multicore designers have achieved much progress onimprovement of memory-dependent performance in cachingsystems and shared memories in general. However, havingapplications running simultaneously and requesting the accessto the shared memories concurrently leads to interference.The performance unpredictability resulting from interferenceat any shared memory level may lead to violationof the timing properties in safety-critical real-time systems.In this paper, we introduce a formal analysis framework forthe schedulability and memory interference of multicore systemswith shared caches and DRAM. We build a multicoresystem model with a ne grained application behavior givenin terms of periodic preemptible tasks, described with explicitread and write access numbers for shared caches andDRAM. We also provide a method to analyze and recommendcandidates for task-to-core reallocation with the goalto nd schedulable congurations if a given system is notschedulable. Our model-based framework is realized usingUppaal and has been used to analyze a case study

  • 115.
    Boudjadar, Jalil
    et al.
    Linköping University.
    Nadjm-Tehrani, Simin
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Schedulability and Memory Interference Analysis of Multicore Preemptive Real-time Systems2017In: 8th ACM/SPEC International Conference on Performance Engineering (ICPE), 2017Conference paper (Refereed)
  • 116.
    Braaf, Joakim
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Introducing Mock framework for Unit Test ina modeling environment2014Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    Testing is an important part in the software development process. Unit testsaim to test individual units in isolation. These units may have dependenciesto their surroundings that make the units hard to test in isolation withoutalso testing the surrounding units. A technique to help isolate these units isto replace the surrounding units with mock objects. This work investigateshow a C++ mock framework can be integrated into a modeling environ-ment’s unit test framework. Several mock frameworks are evaluated, and aproof of concept is created to show that integration is possible. Additionally,ideas for how to use mocks in a model environment are presented.

  • 117.
    Bragazzi Ihrén, Maximilian
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Ingbrant Björs, Henrik
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Visualizing atmospheric data on a mobile platform2017Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    Weather data is important for almost everyone today. Thedaily weather report, home thermometers, and a lot of otherthings affect our every day life. In order to develop betterand more efficient equipment, tools and algorithms, thepeople working with this data need to be able to access it inan easily accessible and easy to read format. In thisresearch, methods of visualizing data on mobile platformsare evaluated based on what researchers in the field wants,since their respective fields might want to use very specificvisualizations. The implementability of these visualizationsare then evaluated, based on the implementations madethroughout this paper. The results show that the researchersknow what they want, and that what they want isimplementable on mobile platforms given some limitationscaused by performance.

  • 118.
    Brehmer, Dan
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Evaluering och optimering av automatisk beståndsindelning2016Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    Beståndsindelning av skog är till stor den en manuell process som kräver mycket tid. De senaste 20 åren har tekniker som Airborne Laser Scanning (ALS) bidragit till en effektivisering av processen genom att generera laserdata som möjliggör skapandet av lättolkade bilder av skogsområden. Ur laser- och bilddata kan skogliga attribut så som trädhöjd, trädtäthet och markhöjd extraheras. Studiens syfte var att utvärdera vilka attribut som var mest relevanta för att särskilja skogsbestånd i ett system som delade in skog i bestånd automatiskt. Vid analys av attributens relevans användes klassificeringsmodeller. Fackmän intervjuades och litteratur studerades. Under studien modifierades systemets algoritmer med ambitionen att höja dess resultat till en tillfredsställande nivå. Studien visade att attribut som är kopplade till skogssköstel har störst relevans vid automatisk beståndsindelning. Trots modifieringar och använding av relevanta attribut lyckades studien inte påvisa att systemet kunde fungera som en egen lösning för beståndsindelning av skog. Däremot var den resulterande beståndsindelningen lämplig att använda som ett komplement vid manuell beståndsindelning.

  • 119.
    Brenner, Jürgen
    et al.
    FernUniversität in Hagen, Germany.
    Keller, Jörg
    FernUniversität in Hagen, Germany.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Executing PRAM Programs on GPUs2012In: Procedia Computer Science, ISSN 1877-0509, Vol. 9, 1799-1806 p.Article in journal (Refereed)
    Abstract [en]

    We present a framework to transform PRAM programs from the PRAM programming language Fork to CUDA C, so that they can be compiled and executed on a Graphics Processor (GPU). This allows to explore parallel algorithmics on a scale beyond toy problems, to which the previous, sequential PRAM simulator restricted practical use. We explain the design decisions and evaluate a prototype implementation consisting of a runtime library and a set of rules to transform simple Fork programs which we for now apply by hand. The resulting CUDA code is almost 100 times faster than the previous simulator for compiled Fork programs and allows to handle larger data sizes. Compared to a sequential program for the same problem, the GPU code might be faster or slower, depending on the Fork program structure, i.e. on the overhead incurred. We also give an outlook how future GPUs might notably reduce the overhead.

  • 120.
    Broman, David
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology. University of Calif Berkeley, CA 94720 USA .
    Derler, Patricia
    University of Calif Berkeley, CA 94720 USA .
    Eidson, John C
    University of Calif Berkeley, CA 94720 USA .
    Temporal Issues in Cyber-Physical Systems2013In: JOURNAL OF THE INDIAN INSTITUTE OF SCIENCE, ISSN 0970-4140, Vol. 93, no 3, 389-402 p.Article, review/survey (Refereed)
    Abstract [en]

    This paper reviews the use of time, clocks, and clock synchronization protocols in cyber-physical systems (CPS). Recent advances in the area of timing suggest avenues of research and potential new application areas. We discuss how introducing timestamps and clocks can help overcome issues such as latency, jitter, and determining correct execution order. Furthermore, we show how system complexity can be reduced and distribution as well as parallelism can be done deterministically. We also point to recent work in raising time to first class citizen status in modeling and implementation. In particular, we describe design and execution environments of CPS and specialized hardware such as predictable timing architectures where time plays a key role.

  • 121.
    Broman, David
    et al.
    Linköping University, Department of Computer and Information Science, PELAB - Programming Environment Laboratory. Linköping University, The Institute of Technology.
    Fritzson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Hedin, Görel
    Lund University, Sweden.
    Åkesson, Johan
    Lund University, Sweden.
    A comparison of two metacompilation approaches to implementing a complex domain-specific language2012In: Proceedings of the 27th Annual ACM Symposium on Applied Computing, Association for Computing Machinery (ACM), 2012, 1919-1921 p.Conference paper (Refereed)
    Abstract [en]

    Operational semantics and attribute grammars are examples of formalisms that can be used for generating compilers. We are interested in finding similarities and differences in how these approaches are applied to complex languages, and for generating compilers of such maturity that they have users in industry.

    As a specific case, we present a comparative analysis of two compilers for Modelica, a language for physical modeling, and which contains numerous compilation challenges. The two compilers are OpenModelica, which is based on big-step operational semantics, and JModelica.org, which is based on reference attribute grammars.

  • 122.
    Brunnerby, Erik
    Linköping University, Department of Computer and Information Science, Software and Systems.
    Android Machine Interface: Integrating anAndroid Mobile Device into an Industrial Control System2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The interaction between humans and industrial machinery have long been dominated by purpose-built hardware made to withstand the tough environment of the factory floor. Advances in hardware and software in the recent decade has made mobile and powerful devices common place, which has prompted this study to evaluate an Android tablet as an interface to control and monitor industrial machinery. This has been done through the implementation of an application used to control a braiding machine. Using this application as a proof of concept and a practical assessment, the study has concluded that an Android device is feasible to use to control and monitor industrial machinery. The study has also evaluated the network performance and security through testing, where it has compared the transport layer protocols TCP and UDP as well as the use of encryption for this implementation.

  • 123.
    Buffoni, Lena
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Pop, AdrianLinköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.Thiele, BernhardLinköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Proceedings of the 56th Conference on Simulation and Modelling (SIMS 56): October, 7-9, 2015, Linköping University, Sweden2015Conference proceedings (editor) (Refereed)
    Abstract [en]

    Welcome

    The 56th Conference on Simulation and Modelling will be held in Linköping, Sweden. Linköping is one of Sweden’s fastest growing cities. The population is constantly increasing and will soon surpass 150 000 inhabitants. It is currently Sweden’s fifth largest city and a part of the expansive region Twin Cities of Sweden. Linköping has long been characterized by world-class high technology in the fields of aviation, IT and the environment. There is a strong force of innovation especially in Mjärdevi Science Park—one of Europe’s leading technology parks, and at the highly ranked university, which stands for excellence and entrepreneurship.

    SIMS is the Scandinavian Simulation Society with members from the five Nordic countries Denmark, Finland, Norway, Sweden and Iceland. The SIMS history goes back to 1959. The goal of SIMS is to further the science and practice of modeling and simulation in all application areas and be a Scandinavian forum for information interchange among modeling and simulation professionals and non-professionals in Denmark, Finland, Norway and Sweden as well as a channel for information exchange between the Scandinavian modeling and simulation community and the international modeling and simulation communities.

    The ambition of the SIMS is to bring the field of modeling and simulation technology to a variety of application fields from energy extraction to building and automotive industries, resulting in more sustainable and ecological systems and reducing energy consumption and waste production. The scientific program includes technical sessions with submitted and invited papers and will cover broad aspects of simulation, modeling and optimization.

    The focus of the conference is split evenly between papers on simulation and optimization in a variety of applied contexts spanning domains such as oil extraction, automotive and building industries and more methodological papers on tools and technologies for simulation and modeling.

    This year we wanted to emphasize the importance of reducing the gap between state of the art methodologies and tools and industrial applications. To this end a number of invited talks, papers and tutorials were centered on tools and methodologies for successful modeling in an industrial context.

    The format of the conference is somewhat changed compared to previous years. This year we have dedicated a half-day before the traditional two-day conference to tutorials, with 3 tutorials presenting stateof- the-art simulation tools.

    Conference highlights:

    • 4 Keynote speeches
    • 40 papers in 2 parallel tracks
    • 3 tutorials
    • Electronic proceedings including all papers and some associated Modelica libraries and models

    Finally, we want to acknowledge the support we received from the conference board and program committee as well as from the SIMS board. Special thanks to our colleagues at this year’s organizers at Linköping University, especially to Åsa Kärrman, and Tina Malmström from Grand Travel Group. The support from the conference sponsors is gratefully acknowledged. Last but not least, thanks to all authors, keynote speakers, and presenters for their contributions to this conference. We wish all participants an enjoyable and inspiring conference.

    Linköping, September 1, 2015

    Lena Buffoni, Adrian Pop and Bernhard Thiele

  • 124.
    Buhaiu, Andrei
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Radio Frequency Remote Control Unit with Gyro and Accelerometer2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Today digital TV receivers (Set-Top-Boxes) are mainly controlled by IR-based remote control units (RCUs). With new services emerging in thereceivers where better browsing and pointing abilities are desirable (VODservices, Web services, games etc), one solution is a new type of RF remotecontrol. An RF RCU has a number of advantages, e.g. when in range, ithas 100% reliable transmission, it is not sensitive to direction, and it doesnot require a free way to the receiver (i.e. it allows the receiver to be hiddenbehind the TV-set or in a cabinet).

  • 125.
    Bäckström, Christer
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Parameterising the Complexity of Planning by the Number of Paths in the Domain-transition Graphs2014In: Proceedings of the 21st European Conference on Artificial Intelligence (ECAI-14), IOS Press, 2014, 33-38 p.Conference paper (Refereed)
    Abstract [en]

    We apply the theory of parameterised complexity to planning, using the concept of fixed-parameter tractability (fpt) which is more relaxed than the usual tractability concept. The parameter we focus on is the maximal number of paths in the domain-transition graphs, and we show that for this parameter, optimal planning is fpt for planning instances with polytree causal graphs and acyclic domain-transition graphs. If this parameter is combined with the additional parameters of domain size for the variables and the treewidth of the causal graph, then planning is fpt also for instances with arbitrary causal graphs. Furthermore, all these parameters are fpt to test in advance. These results also imply that delete-relaxed planning is fpt, even in its recent generalisation to non-binary variables.

  • 126.
    Bäckström, Christer
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Some Fixed Parameter Tractability Results for Planning with Non-Acyclic Domain-Transition Graphs2015In: Twenty-Ninth AAAI Conference on Artificial Intelligence (AAAI-2015), AAAI Press, 2015Conference paper (Refereed)
    Abstract [en]

    Bäckström studied the parameterised complexity of planning when the domain-transition graphs (DTGs) are acyclic. He used the parameters d (domain size), k (number of paths in the DTGs) and w (treewidth of the causal graph), and showed that planning is fixed-parameter tractable (fpt) in these parameters, and fpt in only parameter k if the causal graph is a polytree. We continue this work by considering some additional cases of non-acyclic DTGs. In particular, we consider the case where each strongly connected component (SCC) in a DTG must be a simple cycle, and we show that planning is fpt for this case if the causal graph is a polytree. This is done by first preprocessing the instance to construct an equivalent abstraction and then apply B¨ackstr¨oms technique to this abstraction. We use the parameters d and k, reinterpreting this as the number of paths in the condensation of a DTG, and the two new parameters c (the number of contracted cycles along a path) and pmax (an upper bound for walking around cycles, when not unbounded).

  • 127.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Chen, Yue
    Vienna University of Technology, Austria.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Ordyniak, Sebastian
    Vienna University of Technology, Austria.
    Szeider, Stefan
    Vienna University of Technology, Austria.
    The Complexity of Planning Revisited - A Parameterized Analysis2012In: Proceedings of the Twenty-Sixth AAAI Conference on Artificial Intelligence, AAAI Press, 2012, 1735-1741 p.Conference paper (Refereed)
    Abstract [en]

    The early classifications of the computational complexity of planning under various restrictions in STRIPS (Bylander) and SAS+ (B¨ackstr¨om and Nebel) have influenced following research in planning in many ways. We go back and reanalyse their subclasses, but this time using the more modern tool of parameterized complexity analysis. This provides new results that together with the old results give a more detailed picture of the complexity landscape. We demonstrate separation results not possible with standard complexity theory, which contributes to explaining why certain cases of planning haveseemed simpler in practice than theory has predicted. In particular, we show that certain restrictions of practical interest are tractable in the parameterized sense of the term, and that a simple heuristic is sufficient to make a well-known partialorder planner exploit this fact.

  • 128.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Anders
    University of Pompeu Fabra, Spain.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Automaton Plans2014In: The journal of artificial intelligence research, ISSN 1076-9757, Vol. 51, 255-291 p.Article in journal (Refereed)
    Abstract [en]

    Macros have long been used in planning to represent subsequences of operators. Macros can be used in place of individual operators during search, sometimes reducing the effort required to find a plan to the goal. Another use of macros is to compactly represent long plans. In this paper we introduce a novel solution concept called automaton plans in which plans are represented using hierarchies of automata. Automaton plans can be viewed as an extension of macros that enables parameterization and branching. We provide several examples that illustrate how automaton plans can be useful, both as a compact representation of exponentially long plans and as an alternative to sequential solutions in benchmark domains such as LOGISTICS and GRID. We also compare automaton plans to other compact plan representations from the literature, and find that automaton plans are strictly more expressive than macros, but strictly less expressive than HTNs and certain representations allowing efficient sequential access to the operators of the plan.

  • 129.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Anders
    Universitat Pompeu Fabra, Barcelona, Spain.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    From Macro Plans to Automata Plans2012In: ECAI 2012. 20th European Conference on Artificial Intelligence, 27-31 2012,  August, Montpellier, France, 2012, 91-96 p.Conference paper (Refereed)
    Abstract [en]

    Macros have a long-standing role in planning as a tool for representing repeating subsequences of operators. Macros are useful both for guiding search towards a solution and for representing plans compactly. In this paper we introduce automata plans which consist of hierarchies of finite state automata. Automata plans can be viewed as an extension of macros that enables parametrization and branching. We provide several examples of the utility of automata plans, and prove that automata plans are strictly more expressive than macro plans. We also prove that automata plans admit polynomialtime sequential access of the operators in the underlying “flat” plan, and identify a subset of automata plans that admit polynomial-time random access. Finally, we compare automata plans with other representations allowing polynomial-time sequential access.

  • 130.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Anders
    Universitat Pompeu Fabra, Barcelona, Spain.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Macros, Reactive Plans and Compact Representations2012In: ECAI 2012. 20th European Conference on Artificial Intelligence 27-31 August 2+12, Montpellier, France / [ed] Luc De Raedt, Christian Bessiere, Didier Dubois, Patrick Doherty, Paolo Frasconi, Fredrik Heintz, Peter Lucas, 2012, 85-90 p.Conference paper (Refereed)
    Abstract [en]

    The use and study of compact representations of objects is widespread in computer science. AI planning can be viewed as the problem of finding a path in a graph that is implicitly described by a compact representation in a planning language. However, compact representations of the path itself (the plan) have not received much attention in the literature. Although both macro plans and reactive plans can be considered as such compact representations, little emphasis has been placed on this aspect in earlier work. There are also compact plan representations that are defined by their access properties, for instance, that they have efficient random access or efficient sequential access. We formally compare two such concepts with macro plans and reactive plans, viewed as compact representations, and provide a complete map of the relationships between them.

  • 131.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    A Refined View of Causal Graphs and Component Sizes: SP-Closed Graph Classes and Beyond2013In: The journal of artificial intelligence research, ISSN 1076-9757, Vol. 47, 575-611 p.Article in journal (Refereed)
    Abstract [en]

    The causal graph of a planning instance is an important tool for planning both in practice and in theory. The theoretical studies of causal graphs have largely analysed the computational complexity of planning for instances where the causal graph has a certain structure, often in combination with other parameters like the domain size of the variables. Chen and Giménez ignored even the structure and considered only the size of the weakly connected components. They proved that planning is tractable if the components are bounded by a constant and otherwise intractable. Their intractability result was, however, conditioned by an assumption from parameterised complexity theory that has no known useful relationship with the standard complexity classes. We approach the same problem from the perspective of standard complexity classes, and prove that planning is NP-hard for classes with unbounded components under an additional restriction we refer to as SP-closed. We then argue that most NP-hardness theorems for causal graphs are difficult to apply and, thus, prove a more general result; even if the component sizes grow slowly and the class is not densely populated with graphs, planning still cannot be tractable unless the polynomial hierachy collapses. Both these results still hold when restricted to the class of acyclic causal graphs. We finally give a partial characterization of the borderline between NP-hard and NP-intermediate classes, giving further insight into the problem.

  • 132.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Abstracting Abstraction in Search II: Complexity Analysis2012In: Proceedings of the 5th Annual Symposium on Combinatorial Search, SoCS 2012 / [ed] Daniel Borrajo, Ariel Felner, Richard Korf, Maxim Likhachev, Carlos Linares Lopez, Wheeler Ruml, and Nathan Sturtevant, AAAI Press, 2012, 10-17 p.Conference paper (Refereed)
    Abstract [en]

    Modelling abstraction as a function from the original state space to an abstract state space is a common approach in combinatorial search. Sometimes this is too restricted, though, and we have previously proposed a framework using a more flexible concept of transformations between labelled graphs. We also proposed a number of properties to describe and classify such transformations. This framework enabled the modelling of a number of different abstraction methods in a way that facilitated comparative analyses. It is of particular interest that these properties can be used to capture the concept of refinement without backtracking between levels; how to do this has been an open question for at least twenty years. In this paper, we continue our previous research by analysing the complexity of testing the various transformation properties for both explicit and implicit graph representations.

  • 133.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Abstracting Abstraction in Search with Applications to Planning2012In: Proceedings, Thirteenth International Conference on Principles of Knowledge Representation and Reasoning, AAAI Press, 2012, 446-456 p.Conference paper (Refereed)
    Abstract [en]

    Abstraction has been used in search and planning from the very beginning of AI. Many different methods and formalisms for abstraction have been proposed in the literature but they have been designed from various points of view and with varying purposes. Hence, these methods have been notoriously difficult to analyse and compare in a structured way. In order to improve upon this situation, we present a coherent and flexible framework for modelling abstraction (and abstraction-like) methods based on transformations on labelled graphs. Transformations can have certain method properties that are inherent in the abstraction methods and describe their fundamental modelling characteristics, and they can have certain instance properties that describe algorithmic and computational characteristics of problem instances. The usefulness of the framework is demonstrated by applying it to problems in both search and planning. First, we show that we can capture many search abstraction concepts (such as avoidance of backtracking between levels) and that we can put them into a broader context. We further model five different abstraction concepts from the planning literature. Analysing what method properties they have highlights their fundamental differences and similarities. Finally, we prove that method properties sometimes imply instance properties. Taking also those instance properties into account reveals important information about computational aspects of the five methods.

  • 134.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Algorithms and Limits for Compact Plan Representations2012In: The journal of artificial intelligence research, ISSN 1076-9757, Vol. 44, 141-177 p.Article in journal (Refereed)
    Abstract [en]

    Compact representations of objects is a common concept in computer science. Automated planning can be viewed as a case of this concept: a planning instance is a compact implicit representation of a graph and the problem is to find a path (a plan) in this graph. While the graphs themselves are represented compactly as planning instances, the paths are usually represented explicitly as sequences of actions. Some cases are known where the plans always have compact representations, for example, using macros. We show that these results do not extend to the general case, by proving a number of bounds for compact representations of plans under various criteria, like efficient sequential or random access of actions. In addition to this, we show that our results have consequences for what can be gained from reformulating planning into some other problem. As a contrast to this we also prove a number of positive results, demonstrating restricted cases where plans do have useful compact representations, as well as proving that macro plans have favourable access properties. Our results are finally discussed in relation to other relevant contexts.

  • 135.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Bridging the Gap Between Refinement and Heuristics in Abstraction2013In: IJCAI'13 Proceedings of the Twenty-Third international joint conference on Artificial Intelligence, AAAI Press, 2013, 2261-2267 p.Conference paper (Refereed)
    Abstract [en]

    There are two major uses of abstraction in planning and search: refinement (where abstract solutions are extended into concrete solutions) and heuristics (where abstract solutions are used to compute heuristics for the original search space). These two approaches are usually viewed as unrelated in the literature. It is reasonable to believe, though, that they are related, since they are both intrinsically based on the structure of abstract search spaces. We take the first steps towards formally investigating their relationships, employing our recently introduced framework for analysing and comparing abstraction methods. By adding some mechanisms for expressing metric properties, we can capture concepts like admissibility and consistency of heuristics. We present an extensive study of how such metric properties relate to the properties in the original framework, revealing a number of connections between the refinement and heuristic approaches. This also provides new insights into, for example, Valtorta's theorem and spurious states.

  • 136.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and 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.
    Upper and Lower Time and Space Bounds for Planning2016In: ECAI 2016: 22ND EUROPEAN CONFERENCE ON ARTIFICIAL INTELLIGENCE, IOS PRESS , 2016, Vol. 285, 716-724 p.Conference paper (Refereed)
    Abstract [en]

    There is an extensive literature on the complexity of planning, but explicit bounds on time and space complexity are very rare. On the other hand, problems like the constraint satisfaction problem have been thoroughly analysed in this respect. We provide a number of upper and lower bound results for both plan satisfiability (PSAT) and length-optimal planning (LOP), with an emphasis on monotone planning (where actions have only positive effects) which is used in, for instance, h(+) and similar heuristics. Let v and a be the number of variables and actions, respectively. We consider both restrictions on the number and polarity of preconditions and effects of actions and the PUBS restrictions in SAS(+). For all such classes, we show that PSAT and LOP is either tractable or cannot be solved in subexponential time 2(o(v)) or time 2(o(a)), unless the so-called Exponential Time Hypothesis (ETH) is false. There is also a sharp transition: monotone LOP can be solved in time 2(o(v)) if a is an element of o(v/log v) but not if a is an element of Omega(v). We also study upper bounds and discuss the trade-off between time and space, providing a polynomial-space algorithm for monotone LOP that beats depth-first search in most cases. This raises the important question how lower bounds are affected by polynomial space restrictions.

  • 137.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and 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.
    Ordyniak, Sebastian
    Masaryk University, Czech Republic.
    Szeider, Stefan
    Vienna University of Technology, Austria.
    A complete parameterized complexity analysis of bounded planning2015In: Journal of computer and system sciences (Print), ISSN 0022-0000, E-ISSN 1090-2724, Vol. 81, no 7, 1311-1332 p.Article in journal (Refereed)
    Abstract [en]

    The propositional planning problem is a notoriously difficult computational problem, which remains hard even under strong syntactical and structural restrictions. Given its difficulty it becomes natural to study planning in the context of parameterized complexity. In this paper we continue the work initiated by Downey, Fellows and Stege on the parameterized complexity of planning with respect to the parameter "length of the solution plan." We provide a complete classification of the parameterized complexity of the planning problem under two of the most prominent syntactical restrictions, i.e., the so called PUBS restrictions introduced by Backstrom and Nebel and restrictions on the number of preconditions and effects as introduced by Bylander. We also determine which of the considered fixed-parameter tractable problems admit a polynomial kernel and which do not. (C) 2015 Elsevier Inc. All rights reserved.

  • 138.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Ordyniak, Sebastian
    Masaryk University, Brno, Czech Republic.
    Szeider, Stefan
    Vienna University of Technolgy, Austria.
    Parameterized Complexity and Kernel Bounds for Hard Planning Problems2013In: Algorithms and Complexity: 8th International Conference, CIAC 2013, Barcelona, Spain, May 22-24, 2013. Proceedings / [ed] Paul G. Spirakis & Maria Serna, Springer Berlin/Heidelberg, 2013, 13-24 p.Conference paper (Refereed)
    Abstract [en]

    The propositional planning problem is a notoriously difficult computational problem. Downey et al. (1999) initiated the parameterized analysis of planning (with plan length as the parameter) and Bäckström et al. (2012) picked up this line of research and provided an extensive parameterized analysis under various restrictions, leaving open only one stubborn case. We continue this work and provide a full classification. In particular, we show that the case when actions have no preconditions and at most e postconditions is fixed-parameter tractable if e ≤ 2 and W[1]-complete otherwise. We show fixed-parameter tractability by a reduction to a variant of the Steiner Tree problem; this problem has been shown fixed-parameter tractable by Guo et al. (2007). If a problem is fixed-parameter tractable, then it admits a polynomial-time self-reduction to instances whose input size is bounded by a function of the parameter, called the kernel. For some problems, this function is even polynomial which has desirable computational implications. Recent research in parameterized complexity has focused on classifying fixed-parameter tractable problems on whether they admit polynomial kernels or not. We revisit all the previously obtained restrictions of planning that are fixed-parameter tractable and show that none of them admits a polynomial kernel unless the polynomial hierarchy collapses to its third level.

  • 139.
    Bäckström, Christer
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Jonsson, Peter
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Ståhlberg, Simon
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Fast Detection of Unsolvable Planning Instances Using Local Consistency2013In: Proceedings of the Sixth International Symposium on Combinatorial Search, AAAI Press, 2013, 29-37 p.Conference paper (Refereed)
    Abstract [en]

    There has been a tremendous advance in domain-independent planning over the past decades, and planners have become increasingly efficient at finding plans. However, this has not been paired by any corresponding improvement in detecting unsolvable instances. Such instances are obviously important but largely neglected in planning. In other areas, such as constraint solving and model checking, much effort has been spent on devising methods for detecting unsolvability. We introduce a method for detecting unsolvable planning instances that is loosely based on consistency checking in constraint programming. Our method balances completeness against efficiency through a parameter k: the algorithm identifies more unsolvable instances but takes more time for increasing values of k. We present empirical data for our algorithm and some standard planners on a number of unsolvable instances, demonstrating that our method can be very efficient where the planners fail to detect unsolvability within reasonable resource bounds. We observe that planners based on the h^m heuristic or pattern databases are better than other planners for detecting unsolvability. This is not a coincidence since there are similarities (but also significant differences) between our algorithm and these two heuristic methods.

  • 140.
    Carlqvist, Alexander
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    OpenModelica Support for Figaro Extensions Regarding Fault Analysis2014Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The practical result of this thesis is an extension to OpenModelica that transforms Modelica into Figaro. Modelica is an equation-based object-oriented modeling language. OpenModelica is an open source implementation of Modelica. Figaro is a language used for reliability modeling. Figaro is a general representation formalism that can be transformed into reliability models like fault trees. Figaro was designed for fault analysis. Modelica was designed to model the behavior of physical systems and run dynamic simulations. Because of that, you cannot just break components and analyze what happens to a system. This work enables us to have fault analysis in OpenModelica by transforming our Modelica model into a Figaro model and invoke the Figaro compiler. This lets us break particular components and see what happens to the system. This work is part of an ongoing effort to integrate several modeling environments.

  • 141.
    Carlsson, Daniel
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Development of an ISO 26262 ASIL D compliant verification system2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In 2011 a new functional safety standard for electronic and electrical systems in vehicles waspublished, called ISO 26262. This standard concerns the whole lifecycle of the safety criticalelements used in cars, including the development process of such elements. As the correctnessof the tools used when developing such an element is critical to the safety of the element,the standard includes requirements concerning the software tools used in the development,including verification tools. These requirements mainly specify that a developer of a safetycritical element should provide proof of their confidence in the software tools they are using.One recommended way to gain this confidence is to use tools developed in accordance to a“relevant subset of [ISO 26262]”.This project aims to develop a verification system in accordance to ISO 26262, exploringhow and what specifications should be included in this “relevant subset” of ISO 26262 andto which extent these can be included in their current form. The work concludes with thedevelopment of a single safety element of the verification system, to give an demonstrationof the viability of such a system.

  • 142.
    Chattopadhyay, Sudipta
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    MESS: Memory Performance Debugging on Embedded Multi-core Systems2015In: MODEL CHECKING SOFTWARE, SPIN 2015, SPRINGER-VERLAG BERLIN , 2015, Vol. 9232, 105-125 p.Conference paper (Refereed)
    Abstract [en]

    Multi-core processors have penetrated the modern computing platforms in several dimensions. Such systems aim to achieve high-performance via running computations in parallel. However, the performance of such systems is often limited due to the congestion in shared resources, such as shared caches and shared buses. In this paper, we propose MESS, a performance debugging framework for embedded, multi-core systems. MESS systematically discovers the order of memory-access operations that expose performance bugs due to shared caches. We leverage both on single-core performance profiling and symbolic constraint solving to reveal the interleaved memory-access-pattern that leads to a performance bug. Our baseline framework does not generate any false positive. Besides, its failure to find a solution highlights the absence of performance bugs due to shared caches, for a given input. Finally, we propose an approximate solution that dramatically reduces debugging time, at the cost of a reasonable amount of false positives. Our experiments with several embedded software and a real-life robot controller suggest that we can discover performance bugs in a reasonable time. The implementation of MESS and our experiments are available at https://bitbucket.org/sudiptac/mess.

  • 143.
    Chattopadhyay, Sudipta
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    MESS: Memory Performance Debugging on Embedded Multi-core Systems2015In: Model Checking Software: 22nd International Symposium, SPIN 2015, Stellenbosch, South Africa, August 24-26, 2015, Proceedings / [ed] Bernd Fischer; Jaco Geldenhuys, Springer, 2015, Vol. 9232, 105-125 p.Conference paper (Refereed)
    Abstract [en]

    Multi-core processors have penetrated the modern computing platforms in several dimensions. Such systems aim to achieve high-performance via running computations in parallel. However, the performance of such systems is often limited due to the congestion in shared resources, such as shared caches and shared buses. In this paper, we propose MESS, a performance debugging framework for embedded, multi-core systems. MESS systematically discovers the order of memory-access operations that expose performance bugs due to shared caches. We leverage both on single-core performance profiling and symbolic constraint solving to reveal the interleaved memory-access-pattern that leads to a performance bug. Our baseline framework does not generate any false positive. Besides, its failure to find a solution highlights the absence of performance bugs due to shared caches, for a given input. Finally, we propose an approximate solution that dramatically reduces debugging time, at the cost of a reasonable amount of false positives. Our experiments with several embedded software and a real-life robot controller suggest that we can discover performance bugs in a reasonable time. The implementation of MESS and our experiments are available at https://​bitbucket.​org/​sudiptac/​mess.

  • 144.
    Chattopadhyay, Sudipta
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Eles, Petru
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Peng, Zebo
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Automated software testing of memory performance in embedded GPUs2014In: EMSOFT 2014, Association for Computing Machinery (ACM), 2014Conference paper (Refereed)
    Abstract [en]

    Embedded and real-time software is often constrained by several temporal requirements. Therefore, it is important to design embedded software that meets the required performance goal. The inception of embedded graphics processing units (GPUs) brings new light in developing high-performance embedded software which were previously not suitable for embedded platforms. Whereas GPUs use massive parallelism to obtain high throughput, the overall performance of an application running on embedded GPUs is often limited by memory performance. Therefore, a crucial problem lies in automatically detecting the inefficiency of such software developed for embedded GPUs. In this paper, we propose GUPT, a novel test generation framework that systematically explores and detects poor memory performance of applications running on embedded GPUs. In particular, we systematically combine static analysis with dynamic test generation to expose likely execution scenarios with poor memory performance. Each test case in our generated test suite reports a potential memory-performance issue, along with the detailed information to reproduce the same. We have implemented our test generation framework using GPGPU-Sim, a cycle-accurate simulator and the LLVM compiler infrastructure.We have evaluated our framework for several open-source programs. Our experiments suggest the efficacy of our framework by exposing numerous memory-performance issues in a reasonable time. We also show the usage of our framework in improving the performance of programs for embedded GPUs.

  • 145.
    Chattopadhyay, Sudipta
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Roychoudhury, Abhik
    National University of Singapore, Singapore.
    Cache-Related Preemption Delay Analysis for Multilevel Noninclusive Caches2014In: ACM Transactions on Embedded Computing Systems, ISSN 1539-9087, E-ISSN 1558-3465, Vol. 13, no 147Article in journal (Refereed)
    Abstract [en]

    With the rapid growth of complex hardware features, timing analysis has become an increasingly difficult problem. The key to solving this problem lies in the precise and scalable modeling of performance-enhancing processor features (e.g., cache). Moreover, real-time systems are often multitasking and use preemptive scheduling, with fixed or dynamic priority assignment. For such systems, cache related preemption delay (CRPD) may increase the execution time of a task. Therefore, CRPD may affect the overall schedulability analysis. Existing works propose to bound the value of CRPD in a single-level cache. In this article, we propose a CRPD analysis framework that can be used for a two-level, noninclusive cache hierarchy. In addition, our proposed framework is also applicable in the presence of shared caches. We first show that CRPD analysis faces several new challenges in the presence of a multilevel, noninclusive cache hierarchy. Our proposed framework overcomes all such challenges and we can formally prove the correctness of our framework. We have performed experiments with several subject programs, including an unmanned aerial vehicle (UAV) controller and an in-situ space debris monitoring instrument. Our experimental results suggest that we can provide sound and precise CRPD estimates using our framework.

  • 146.
    Chattopadhyay, Sudipta
    et al.
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, Faculty of Science & Engineering.
    Roychoudhury, Abhik
    National University of Singapore.
    Rosén, Jakob
    Linköping University, Department of Computer and Information Science, ESLAB - Embedded Systems Laboratory.
    Eles, Petru
    Linköping University, Department of Computer and Information Science, ESLAB - Embedded Systems Laboratory. Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Peng, Zebo
    Linköping University, Department of Computer and Information Science, ESLAB - Embedded Systems Laboratory. Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Time-Predictable Embedded Software on Multi-Core Platforms: Analysis and Optimization2014In: Foundations and Trends in Electronic Design Automation, ISSN 1551-3939, Vol. 8, no 3-4, 199-356 p.Article in journal (Refereed)
    Abstract [en]

    Multi-core architectures have recently gained popularity due to their high-performance and low-power characteristics. Most of the modern desktop systems are now equipped with multi-core processors. Despite the wide-spread adaptation of multi-core processors in desktop systems, using such processors in embedded systems still poses several challenges. Embedded systems are often constrained by several extra-functional aspects, such as time. Therefore, providing guarantees for time-predictable execution is one of the key requirements for embedded system designers. Multi-core processors adversely affect the time-predictability due to the presence of shared resources, such as shared caches and shared buses. In this contribution, we shall first discuss the challenges imposed by multi-core architectures in designing time-predictable embedded systems. Subsequently, we shall describe, in details, a comprehensive solution to guarantee time-predictable execution on multi-core platforms. Besides, we shall also perform a discussion of different techniques to provide an overview of the state-of-the-art solutions in this topic. Through this work, we aim to provide a solid background on recent trends of research towards achieving time-predictability on multi-cores. Besides, we also highlight the limitations of the state-of-the-art and discuss future research opportunities and challenges to accomplish time-predictable execution on multi-core platforms.

  • 147.
    Chen, Hubie
    et al.
    Universitat Pompeu Fabra, Barcelona, Spain.
    Wrona, Michal
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Guarded Ord-Horn: A Tractable Fragment of Quantified Constraint Satisfaction2012Conference paper (Other academic)
    Abstract [en]

    The first-order theory of dense linear orders without endpoints is well-known to be PSPACE-complete. We present polynomial-time tractability results for fragments of this theory which are defined by syntactic restriction, in particular, our fragments can be described using the framework of quantified constraint satisfaction over Ord-Horn clauses.

  • 148.
    Chen, Yi-Ching
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Co-design of Fault-Tolerant Systems with Imperfect Fault Detection2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In recent decades, transient faults have become a critical issue in modernelectronic devices. Therefore, many fault-tolerant techniques have been proposedto increase system reliability, such as active redundancy, which can beimplemented in both space and time dimensions. The main challenge of activeredundancy is to introduce the minimal overhead of redundancy and to schedulethe tasks. In many pervious works, perfect fault detectors are assumed to simplifythe problem. However, the induced resource and time overheads of suchfault detectors make them impractical to be implemented. In order to tacklethe problem, an alternative approach was proposed based on imperfect faultdetectors.

    So far, only software implementation is studied for the proposed imperfectfault detection approach. In this thesis, we take hardware-acceleration intoconsideration. Field-programmable gate array (FPGA) is used to accommodatetasks in hardware. In order to utilize the FPGA resources efficiently, themapping and the selection of fault detectors for each task replica have to be carefullydecided. In this work, we present two optimization approaches consideringtwo FPGA technologies, namely, statically reconfigurable FPGA and dynamicallyreconfigurable FPGA respectively. Both approaches are evaluated andcompared with the proposed software-only approach by extensive experiments.

  • 149.
    Cichowski, Patrick
    et al.
    FernUniversität in Hagen, Germany.
    Keller, Jörg
    FernUniversität in Hagen, Germany.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Energy-efficient Mapping of Task Collections onto Manycore Processors2013In: Proceedings of MULTIPROG'13 workshop at HiPEAC'13 / [ed] E. Ayguade et al. (eds.), 2013Conference paper (Refereed)
    Abstract [en]

    Streaming applications consist of a number of tasks that all run concurrently, and that process data at certain rates. On manycore processors, the tasks of the streaming application must be mapped onto the cores. While load balancing of such applications has been considered, especially in the MPSoC community, we investigate energy-efficient mapping of such task collections onto manycore processors. We first derive rules that guide the mapping process and show that as long as dynamic power consumption dominates static power consumption, the latter can be ignored and the problem reduces to load balancing. When however, as expected in the coming years, static power consumption will be a notable fraction of total power consumption, then an energy-efficient mapping must take it into account, e.g. by temporary shutdown of cores or by restricting the number of cores. We validate our findings with synthetic and real-world applications on the Intel SCC manycore processor.

  • 150.
    Cichowski, Patrick
    et al.
    FernUniversität in Hagen, Germany.
    Keller, Jörg
    FernUniversität in Hagen, Germany.
    Kessler, Christoph
    Linköping University, Department of Computer and Information Science, Software and Systems. Linköping University, The Institute of Technology.
    Modelling Power Consumption of the Intel SCC2012In: Proceedings of the 6th Many-core Applications Research Community (MARC) Symposium / [ed] Eric Noulard, HAL Archives Ouvertes , 2012Conference paper (Refereed)
    Abstract [en]

    The Intel SCC manycore processor supports energy-efficient computing by dynamic voltage and frequency scaling of cores on a fine-grained level. In order to enable the use of that feature in application-level energy optimizations, we report on experiments to measure power consumption in different situations. We process those measurements by a least-squares error analysis to derive the parameters of popular models for power consumption which are used on an algorithmic level. Thus, we provide a link between the worlds of hardware and high-level algorithmics.

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