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  • 1.
    Abdulla, Parosh Aziz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Chen, Yu-Fang
    Holik, Lukag
    Vojnar, Tomas
    Mediating for reduction (on minimizing alternating Buchi automata)2014In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 552, p. 26-43Article in journal (Refereed)
    Abstract [en]

    We propose a new approach for minimizing alternating Buchi automata (ABA). The approach is based on the mediated equivalence on states of an ABA, which is the maximal equivalence contained in the mediated preorder. Two states p and q are related by the mediated preorder if there is a mediator (mediating state) which forward simulates p and backward simulates q. Under further conditions, letting a computation on some word jump from q to p preserves the language as the automaton can anyway already accept the word without jumps by runs through the mediator. We further show how the mediated equivalence can be computed efficiently. Finally, we show that, compared to the standard forward simulation equivalence, the mediated equivalence can yield much larger reductions when applied within the process of complementing Buchi automata where ABA are used as an intermediate model.

  • 2.
    Abdulla, Parosh Aziz
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Delzanno, Giorgio
    Univ Genoa, I-16126 Genoa, Italy..
    Rezine, Othmane
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Uppsala Univ, Uppsala, Sweden..
    Sangnier, Arnaud
    Univ Paris Diderot, CNRS, LIAFA, Paris, France..
    Traverso, Riccardo
    FBK, Trento, Italy..
    Parameterized verification of time-sensitive models of ad hoc network protocols2016In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 612, p. 1-22Article in journal (Refereed)
    Abstract [en]

    We study decidability and undecidability results for parameterized verification of a formal model of timed Ad Hoc network protocols. The communication topology is defined by an undirected graph and the behaviour of each node is defined by a timed automaton communicating with its neighbours via broadcast messages. We consider parameterized verification problems formulated in terms of reachability. In particular we are interested in searching for an initial configuration from which an individual node can reach an error state. We study the problem for dense and discrete time and compare the results with those obtained for (fully connected) networks of timed automata.

  • 3. Chilton, Chris
    et al.
    Jonsson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Kwiatkowska, Marta
    An algebraic theory of interface automata2014In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 549, p. 146-174Article in journal (Refereed)
    Abstract [en]

    We formulate a compositional specification theory for interface automata, where a component model specifies the allowed sequences of input and output interactions with the environment. A trace-based linear-time refinement is provided, which is the weakest preorder preserving substitutivity of components, and is weaker than the classical alternating simulation defined on interface automata. Since our refinement allows a component to be refined by refusing to produce any output, we also define a refinement relation that guarantees safety and progress. The theory includes the operations of parallel composition to support the structural composition of components, logical conjunction and disjunction for independent development, hiding to support abstraction of interfaces, and quotient for incremental synthesis of components. Our component formulation highlights the algebraic properties of the specification theory for both refinement preorders, and is shown to be fully abstract with respect to observation of communication mismatches. Examples of independent and incremental component development are provided.

  • 4. Gambino, Nicola
    et al.
    Garner, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    The identity type weak factorisation system2008In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 409, no 1, p. 94-109Article in journal (Refereed)
    Abstract [en]

    We show that the classifying category C(T) of a dependent type theory T with axioms for identity types admits a non-trivial weak factorisation system. We provide an explicit characterisation of the elements of both the left class and the right class of the weak factorisation system. This characterisation is applied to relate identity types and the homotopy theory of groupoids.

  • 5.
    Grinchtein, Olga
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Jonsson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Leucker, Martin
    Learning of event-recording automata2010In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 411, no 47, p. 4029-4054Article in journal (Refereed)
  • 6.
    Janson, Svante
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics, Analysis and Applied Mathematics.
    Renewal theory in the analysis of tries and strings2012In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 416, p. 33-54Article in journal (Refereed)
    Abstract [en]

    We give a survey of a number of simple applications of renewal theory to problems on random strings and tries: insertion depth, size, insertion mode and imbalance of tries; variations for b-tries and Patricia tries; Khodak and Tunstall codes.

  • 7.
    Malmberg, Filip
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Centre for Image Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Lindblad, Joakim
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Centre for Image Analysis.
    Sladoje, Natasa
    Faculty of Technical Sciences, University of Novi Sad.
    Nyström, Ingela
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Centre for Image Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    A Graph-based Framework for Sub-pixel Image Segmentation2011In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 412, no 15, p. 1338-1349Article in journal (Refereed)
    Abstract [en]

    Many image segmentation methods utilize graph structures for representing images, where the flexibility and generality of the abstract structure is beneficial. By using a fuzzy object representation, i.e., allowing partial belongingness of elements to image objects, the unavoidable loss of information when representing continuous structures by finite sets is significantly reduced,enabling feature estimates with sub-pixel precision.This work presents a framework for object representation based on fuzzysegmented graphs. Interpreting the edges as one-dimensional paths betweenthe vertices of a graph, we extend the notion of a graph cut to that of a located cut, i.e., a cut with sub-edge precision. We describe a method for computing a located cut from a fuzzy segmentation of graph vertices. Further,the notion of vertex coverage segmentation is proposed as a graph theoretic equivalent to pixel coverage segmentations and a method for computing such a segmentation from a located cut is given. Utilizing the proposed framework,we demonstrate improved precision of area measurements of synthetic two-dimensional objects. We emphasize that although the experiments presented here are performed on two-dimensional images, the proposed framework is defined for general graphs and thus applicable to images of any dimension.

  • 8. Milner, Robin
    et al.
    Parrow, Joachim
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Walker, David
    Modal Logics for Mobile Processes1993In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 114, no 1, p. 149-171Article in journal (Refereed)
    Abstract [en]

    In process algebras, bisimulation equivalence is typically defined directly in terms of the operational rules of action; it also has an alternative characterization in terms of a simple modal logic (sometimes called Hennessy-Milner logic). This paper first defines two forms of bisimulation equivalence for the π-calculus, a process algebra which allows dynamic reconfiguration among processes; it then explores a family of possible logics, with different modal operators. It is proven that two of these logics characterize the two bisimulation equivalences. Also, the relative expressive power of all the logics is exhibited as a lattice. The results are applicable to most value-passing process algebras.

  • 9. Nagy, Benedek
    et al.
    Strand, Robin
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Centre for Image Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Approximating Euclidean circles by neighbourhood sequences in a hexagonal grid2011In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 412, no 15, p. 1364-1377Article in journal (Refereed)
  • 10.
    Parrow, Joachim
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Submodule Construction as Equation Solving in CCS1989In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 68, no 2, p. 175-202Article in journal (Refereed)
  • 11.
    Strand, Robin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Centre for Image Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Nagy, Benedek
    Borgefors, Gunilla
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Centre for Image Analysis. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Digital distance functions on three-dimensional grids2011In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 412, no 15, p. 1350-1363Article in journal (Refereed)
  • 12.
    Strand, Robin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Normand, Nicolas
    Distance transform computation for digital distance functions2012In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 448, p. 80-93Article in journal (Refereed)
    Abstract [en]

    In image processing, the distance transform (DT), in which each object grid point is assigned the distance to the closest background grid point, is a powerful and often used tool. In this paper, distance functions defined as minimal cost-paths are used and a number of algorithms that can be used to compute the DT are presented. We give proofs of the correctness of the algorithms.

  • 13. Touili, Tayssir
    et al.
    Atig, Mohamed Faouzi
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Verifying parallel programs with dynamic communication structures2010In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 411, p. 3460-3468Article in journal (Refereed)
  • 14.
    Uscka-Wehlou, Hanna
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Digital lines with irrational slopes2007In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 377, no 1-3, p. 157-169Article in journal (Refereed)
    Abstract [en]

    How to construct a digitization of a straight line and how to be able to recognize a straight line in a set of pixels are very important topics in computer graphics. The aim of the present paper is to give a mathematically exact and consistent description of digital straight lines according to Rosenfeld's definition. The digitizations of lines with slopes 0 < a < 1, where a is irrational, are considered. We formulate a definition of digitization runs, and formulate and prove theorems containing necessary and sufficient conditions for digital straightness. The proof was successfully constructed using only methods of elementary mathematics. The developed and proved theory can be used in research into the theory of digital lines, their symmetries, translations, etc.

  • 15.
    Uscka-Wehlou, Hanna
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Mathematics.
    Two Equivalence Relations on Digital Lines with Irrational Slopes. A Continued Fraction Approach to Upper Mechanical Words2009In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 410, no 38--40, p. 3655-3669Article in journal (Refereed)
    Abstract [en]

    We examine the influence of the elements of the continued fraction (CF) expansion of irrational positive a less than 1 on the construction of runs in the digitization of the positive half line y=ax or, equivalently, on the run-hierarchical structure of the upper mechanical word with slope a and intercept 0. Special attention is given to the CF elements equal to 1.We define two complementary equivalence relations on the set of slopes, based on their CF expansions. A new description of digital lines is presented; we show how to define a straight line or upper mechanical word by two sequences of positive integers fulfilling some extra conditions. These equivalence relations and this new description enable us to analyze the construction of digital lines and upper mechanical words. The analysis of suprema of equivalence classes under one of these relations leads to a result which involves Fibonacci numbers.

1 - 15 of 15
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