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  • 1.
    Bernard, Florian
    et al.
    University Of Bonn, Bonn, Germany.
    Cremers, Daniel
    Technische Universität München, München, Germany.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Sparse Quadratic Optimisation over the Stiefel Manifold with Application to Permutation Synchronisation2021Ingår i: Advances in Neural Information Processing Systems / [ed] Ranzato M.; Beygelzimer A.; Dauphin Y.; Liang P.S.; Wortman Vaughan J., Maryland Heights, MO: Morgan Kaufmann Publishers, 2021, Vol. 30, s. 25256-25266Konferensbidrag (Refereegranskat)
    Abstract [en]

    We address the non-convex optimisation problem of finding a sparse matrix on the Stiefel manifold (matrices with mutually orthogonal columns of unit length) that maximises (or minimises) a quadratic objective function. Optimisation problems on the Stiefel manifold occur for example in spectral relaxations of various combinatorial problems, such as graph matching, clustering, or permutation synchronisation. Although sparsity is a desirable property in such settings, it is mostly neglected in spectral formulations since existing solvers, e.g. based on eigenvalue decomposition, are unable to account for sparsity while at the same time maintaining global optimality guarantees. We fill this gap and propose a simple yet effective sparsity-promoting modification of the Orthogonal Iteration algorithm for finding the dominant eigenspace of a matrix. By doing so, we can guarantee that our method finds a Stiefel matrix that is globally optimal with respect to the quadratic objective function, while in addition being sparse. As a motivating application we consider the task of permutation synchronisation, which can be understood as a constrained clustering problem that has particular relevance for matching multiple images or 3D shapes in computer vision, computer graphics, and beyond. We demonstrate that the proposed approach outperforms previous methods in this domain. © 2021 Neural information processing systems foundation. All rights reserved.

  • 2.
    Bernard, Florian
    et al.
    MPI Informatics, Saarland Informatics Campus, Saarbrücken, Germany.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Goncalves, Jorge
    LCSB, University of Luxembourg, Esch-sur-Alzette, Luxembourg.
    Theobalt, Christian
    MPI Informatics, Saarland Informatics Campus, Saarbrücken, Germany.
    Synchronisation of partial multi-matchings via non-negative factorisations2019Ingår i: Pattern Recognition, ISSN 0031-3203, E-ISSN 1873-5142, Vol. 92, s. 146-155Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work we study permutation synchronisation for the challenging case of partial permutations, which plays an important role for the problem of matching multiple objects (e.g. images or shapes). The term synchronisation refers to the property that the set of pairwise matchings is cycle-consistent, i.e. in the full matching case all compositions of pairwise matchings over cycles must be equal to the identity. Motivated by clustering and matrix factorisation perspectives of cycle-consistency, we derive an algo- rithm to tackle the permutation synchronisation problem based on non-negative factorisations. In order to deal with the inherent non-convexity of the permutation synchronisation problem, we use an initialisation procedure based on a novel rotation scheme applied to the solution of the spectral relaxation. Moreover, this rotation scheme facilitates a convenient Euclidean projection to obtain a binary solution after solving our relaxed problem. In contrast to state-of-the-art methods, our approach is guaranteed to produce cycle-consistent results. We experimentally demonstrate the efficacy of our method and show that it achieves better results compared to existing methods. © 2019 Elsevier Ltd

  • 3.
    Bernard, Florian
    et al.
    MPI Informat, Saarbrucken, Germany & Saarland Informat Campus, Saarland, Germany.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Swoboda, Paul
    MPI Informat, Saarbrucken, Germany & Saarland Informat Campus, Saarland, Germany.
    Theobalt, Christian
    MPI Informat, Saarbrucken, Germany & Saarland Informat Campus, Saarland, Germany.
    HiPPI: Higher-order projected power iterations for scalable multi-matching2019Ingår i: IEEE International Conference on (ICCV) Computer Vision, ISSN 1550-5499, Vol. 2019-October, s. 10283-10292, artikel-id 9010401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The matching of multiple objects (e.g. shapes or images) is a fundamental problem in vision and graphics. In order to robustly handle ambiguities, noise and repetitive patterns in challenging real-world settings, it is essential to take geometric consistency between points into account. Computationally, the multi-matching problem is difficult. It can be phrased as simultaneously solving multiple (NP-hard) quadratic assignment problems (QAPs) that are coupled via cycle-consistency constraints. The main limitations of existing multi-matching methods are that they either ignore geometric consistency and thus have limited robustness, or they are restricted to small-scale problems due to their (relatively) high computational cost. We address these shortcomings by introducing a Higher-order Projected Power Iteration method, which is (i) efficient and scales to tens of thousands of points, (ii) straightforward to implement, (iii) able to incorporate geometric consistency, (iv) guarantees cycle-consistent multi-matchings, and (iv) comes with theoretical convergence guarantees. Experimentally we show that our approach is superior to existing methods. © 2019 IEEE.

  • 4.
    Gao, Maolin
    et al.
    Technical University of Munich, Munich, Germany.
    Lähner, Zorah
    Technical University of Munich, Munich, Germany; University of Siegen, Siegen, Germany.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Cremers, Daniel
    Technical University of Munich, Munich, Germany.
    Bernard, Florian
    Technical University of Munich, Munich, Germany.
    Isometric multi-shape matching2021Ingår i: Proceedings of the IEEE Computer Society Conference on Computer Vision and Pattern Recognition, Washington, DC: IEEE, 2021, s. 14178-14188Konferensbidrag (Refereegranskat)
    Abstract [en]

    Finding correspondences between shapes is a fundamental problem in computer vision and graphics, which is relevant for many applications, including 3D reconstruction, object tracking, and style transfer. The vast majority of correspondence methods aim to find a solution between pairs of shapes, even if multiple instances of the same class are available. While isometries are often studied in shape correspondence problems, they have not been considered explicitly in the multi-matching setting. This paper closes this gap by proposing a novel optimisation formulation for isometric multi-shape matching. We present a suitable optimisation algorithm for solving our formulation and provide a convergence and complexity analysis. Our algorithm obtains multi-matchings that are by construction provably cycle-consistent. We demonstrate the superior performance of our method on various datasets and set the new state-ofthe-art in isometric multi-shape matching. © 2021 IEEE

  • 5.
    Markdahl, J.
    et al.
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Belval, Luxembourg.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Goncalves, J.
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Belval, Luxembourg.
    High-dimensional Kuramoto models on Stiefel manifolds synchronize complex networks almost globally2020Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 113, artikel-id 108736Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Kuramoto model of coupled phase oscillators is often used to describe synchronization phenomena in nature. Some applications, e.g., quantum synchronization and rigid-body attitude synchronization, involve high-dimensional Kuramoto models where each oscillator lives on the n-sphere or SO(n). These manifolds are special cases of the compact, real Stiefel manifold St(p,n). Using tools from optimization and control theory, we prove that the generalized Kuramoto model on St(p,n) converges to a synchronized state for any connected graph and from almost all initial conditions provided (p,n) satisfies p≤2/3n−1 and all oscillator frequencies are equal. This result could not have been predicted based on knowledge of the Kuramoto model in complex networks over the circle. In that case, almost global synchronization is graph dependent; it applies if the network is acyclic or sufficiently dense. This paper hence identifies a property that distinguishes many high-dimensional generalizations of the Kuramoto models from the original model. © 2019 Elsevier Ltd

  • 6.
    Markdahl, Johan
    et al.
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Luxembourg, Luxembourg.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Gonçalves, Jorge
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Luxembourg, Luxembourg.
    Towards Almost Global Synchronization on the Stiefel Manifold2018Ingår i: 2018 IEEE Conference on Decision and Control (CDC), Miami Beach, FL, USA, Dec. 17-19, 2018, Miami Beach, Florida: IEEE, 2018, s. 496-501Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Kuramoto model evolves on the circle, i.e., the 1-sphere S1. A graph G is referred to as S1 -synchronizing if the Kuramoto model on G synchronizes almost globally. This paper generalizes the Kuramoto model and the concept of synchronizing graphs to the Stiefel manifold St (p, n). Previous work on generalizations of the Kuramoto model have largely been influenced by results and techniques that pertain to the original model. It was recently shown that all connected graphs are Sn -synchronizing for all n ≥ 2. However, that does not hold for = 1. Previous results on generalized models may thus have been overly conservative. The n-sphere is a special case of the Stiefel manifold, namely St(1, n+1). As such, it is natural to ask for the extent to which the results on Sn can be extended to the Stiefel manifold. This paper shows that all connected graphs are St(p, n) -synchronizing provided the pair (p, n) satisfies p ≤ [2n/3]-1. © Copyright 2019 IEEE - All rights reserved.

  • 7.
    Moggi, E.
    et al.
    DIBRIS, Genova University, Genova, Italy.
    Taha, Walid
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Sound over-approximation of probabilities2020Ingår i: Acta Cybernetica, ISSN 0324-721X, Vol. 24, nr 3, s. 269-285Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Safety analysis of high confidence systems requires guaranteed bounds on the probabilities of events of interest. Establishing the correctness of algorithms that aim to compute such bounds is challenging. We address this problem in three steps. First, we use monadic transition systems (MTS) in the category of sets as a framework for modeling discrete time systems. MTS can capture different types of system behaviors, but we focus on a combination of non-deterministic and probabilistic behaviors that often arises when modeling complex systems. Second, we use the category of posets and monotonic maps as a setting to define and compare approximations. In particular, for the MTS of interest, we consider approximations of their configurations based on complete lattices. Third, by restricting to finite lattices, we obtain algorithms that compute over-approximations, i.e., bounds from above within some partial order of approximants, of the system configuration after n steps. Interestingly, finite lattices of “interval probabilities” may fail to accurately approximate configurations that are both non-deterministic and probabilistic, even for deterministic (and continuous) system dynamics. However, better choices of finite lattices are available. © 2020 University of Szeged, Institute of Informatics. All rights reserved.

  • 8.
    Sidorenko, Galina
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Fedorov, Aleksei
    Lund University, Lund, Sweden.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi. University of Passau, Passau, Germany.
    Towards a Complete Safety Framework for Longitudinal Driving2022Ingår i: IEEE Transactions on Intelligent Vehicles, ISSN 2379-8858, E-ISSN 2379-8904, Vol. 7, nr 4, s. 809-814Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Formal models for the safety validation of autonomous vehicles have become increasingly important. To this end, we present a safety framework for longitudinal automated driving. This framework allows calculating minimum safe inter-vehicular distances for arbitrary ego vehicle control policies. We use this framework to enhance the Responsibility-Sensitive Safety (RSS) model and models based on it, which fail to cover situations where the ego vehicle has a higher decelerating capacity than its preceding vehicle. For arbitrary ego vehicle control policies, we show how our framework can be applied by substituting real (possibly computationally intractable) controllers with upper bounding functions. This comprises a general approach for longitudinal safety, where safety guarantees for the upper-bounded system are equivalent to those for the original system but come at the expense of larger inter-vehicular distances. 

  • 9.
    Sidorenko, Galina
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Plöger, Daniel
    Institute of Communication Networks, Hamburg University of Technology, Hamburg, Germany.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Emergency braking with ACC: how much does V2V communication help2022Ingår i: IEEE Networking Letters, E-ISSN 2576-3156, Vol. 4, nr 3, s. 157-161Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper provides a safety analysis for emergency braking scenarios involving consecutive vehicles which utilize adaptive cruise control (ACC) with a constant-distance policy together with vehicle-to-vehicle (V2V) communication. We identify analytically, how the minimum safe inter-vehicle distance(IVD) that allows avoiding rear-end collision can be shortened with the use of electronic emergency brake lights and derive the explicit dependency of such IVDs on V2V communication time delay. We further show how these results can be used to compute probabilities of safe braking in the presence of packet losses.

  • 10.
    Sidorenko, Galina
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Sjöberg, Katrin
    Volvo Autonomous Solutions, Göteborg, Sweden.
    Fedorov, Aleksei
    Lund University, Lund, Sweden.
    Vinel, Alexey
    Safety of Automatic Emergency Braking in Platooning2022Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 71, nr 3, s. 2319-2332Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A platoon comprises a string of consecutive highly automated vehicles traveling together. Platooning allows for increased road utilization and reduced fuel consumption due to short inter-vehicular distances. Safety in terms of guaranteeing no rear-end collisions is of utmost importance for platooning systems to be deployed in practice. We compare how safely emergency braking can be handled by emerging V2V communications on the one hand and by radar-based measurements of existing AEBS on the other. We show that even under conservative assumptions on the V2V communications, such an approach significantly outperforms AEBS with an ideal radar sensor in terms of allowed inter-vehicle distances and response times. Furthermore, we design two emergency braking strategies for platooning based on V2V communications. The first braking strategy assumes centralized coordination by the leading vehicle and exploits necessary optimal conditions of a constrained optimization problem, whereas the second -- the more conservative solution -- assumes only local information and is distributed in nature. Both strategies are also compared with the AEBS.

  • 11.
    Sidorenko, Galina
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Sjöberg, Katrin
    Scania CV AB, Södertälje, Sweden.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Vehicle-to-Vehicle Communication for Safe and Fuel-Efficient Platooning2020Ingår i: 2020 IEEE Intelligent Vehicles Symposium (IV), Piscataway: Institute of Electrical and Electronics Engineers (IEEE), 2020, s. 795-802, artikel-id 9304719Konferensbidrag (Refereegranskat)
    Abstract [en]

    A platoon consists of a string of vehicles traveling close together. Such tight formation allows for increased road throughput and reduced fuel consumption due to decreased air resistance. Furthermore, sensors and control algorithms can be used to provide a high level of automation. In this context, safety – in terms of no rear-end collisions – is a key property that needs to be assured. We investigate how vehicle-to-vehicle communication can be used to reduce inter-vehicle distances while guaranteeing safety in emergency braking scenarios. An optimization-based modeling scheme is presented that, under certain restrictions, provides an analytical calculation of inter-vehicle distances for safe braking. In contrast to earlier simulation-based approaches, the framework allows for computationally efficient solutions with explicit guarantees. Two approaches for computing braking strategies in emergency scenarios are proposed. The first assumes centralized coordination by the leading vehicle and exploits necessary optimal conditions of a constrained optimization problem, whereas the second – the more conservative solution – assumes only local information and is distributed in nature. We illustrate the usefulness of the approaches through several computational simulations. © 2020 IEEE.

  • 12.
    Sidorenko, Galina
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Cooperation for Ethical Autonomous DrivingIngår i: Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The success in the adoption of autonomous vehicles is dependent on their ability to solve rarely occurring safety-critical corner cases. Vehicular communications (V2X) aim at improving safety and efficiency of autonomous driving by adding the capability of explicit inter-vehicular information exchange. We argue that V2X enables another important function, namely the support of ethical driving decisions. In this article, we explain our envisioned methodology of an ethical cooperative driving interaction protocol design (including what to communicate and how to act based on the received information). Cooperative manoeuvring empowered by the ethical V2X is a new research direction we promote in the autonomous driving research agenda.

  • 13.
    Sidorenko, Galina
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi. Karlsruhe Institute of Technology, Karlsruhe, Germany.
    Ethical V2X: Cooperative Driving as the only Ethical Path to Multi-Vehicle Safety2023Ingår i: 2023 IEEE 98th Vehicular Technology Conference (VTC2023-Fall), IEEE, 2023Konferensbidrag (Refereegranskat)
    Abstract [en]

    We argue that an information exchange between vehicles via the vehicular communications is the foundation for ethical driving. In other words - autonomous vehicles must be cooperative to be able to resolve ethical dilemmas in a multi-vehicle scenario. We show this by exploring the minimal setting of a longitudinal driving in a formation of three vehicles. © 2023 IEEE.

  • 14.
    Thunberg, Johan
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Bernard, Florian
    University of Bonn, Bonn, Germany.
    Non-negative Spherical Relaxations for Universe-Free Multi-matching and Clustering2023Ingår i: Image Analysis: 22nd Scandinavian Conference, SCIA 2023, Sirkka, Finland, April 18–21, 2023, Proceedings, Part II / [ed] Gade, Rikke; Felsberg, Michael; Kämäräinen, Joni-Kristian, Cham: Springer, 2023, Vol. 13886, s. 260-277Konferensbidrag (Refereegranskat)
    Abstract [en]

    We propose a novel non-negative spherical relaxation for optimization problems over binary matrices with injectivity constraints, which in particular has applications in multi-matching and clustering. We relax respective binary matrix constraints to the (high-dimensional) non-negative sphere. To optimize our relaxed problem, we use a conditional power iteration method to iteratively improve the objective function, while at same time sweeping over a continuous scalar parameter that is (indirectly) related to the universe size (or number of clusters). Opposed to existing procedures that require to fix the integer universe size before optimization, our method automatically adjusts the analogous continuous parameter. Furthermore, while our approach shares similarities with spectral multi-matching and spectral clustering, our formulation has the strong advantage that we do not rely on additional post-processing procedures to obtain binary results. Our method shows compelling results in various multi-matching and clustering settings, even when compared to methods that use the ground truth universe size (or number of clusters). © 2023, The Author(s), under exclusive license to Springer Nature Switzerland AG.

  • 15.
    Thunberg, Johan
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Bischoff, Daniel
    Multimedia Communications Lab (KOM), Technical University of Darmstadt, Darmstadt, Germany.
    Schiegg, Florian A.
    Corporate Research, Robert Bosch GmbH, Hildesheim, Germany.
    Meuser, Tobias
    Multimedia Communications Lab (KOM), Technical University of Darmstadt, Darmstadt, Germany.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Unreliable V2X communication in cooperative driving: Safety times for emergency braking2021Ingår i: IEEE Access, E-ISSN 2169-3536, Vol. 9, s. 148024-148036Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cooperative driving is a promising paradigm to improve traffic efficiency and safety. In congested traffic scenarios, such cooperation allows for safe maneuvering and driving with small inter-vehicle spatial gaps. The vehicles involved coordinate their movements in real-time and continuously update each other about their maneuver execution status by means of Vehicle-to-Everything (V2X) communication. However, unreliable V2X communication increases the Age of Information (AoI) of vehicles' status updates, posing a challenge in situations where emergency braking is required during cooperative maneuvering. To address the interplay between unreliable V2X communication and the resulting impact on traffic safety, we introduce a so-called safety time function, specifically designed for cooperative driving use-cases. The safety time function provides the time available for a vehicle to react to an unexpected event of another vehicle - such as emergency braking to avoid a collision. We provide a computationally efficient algorithm for the computation of safety time functions, which allows for efficient and safe cooperative maneuver planning - even in dense traffic scenarios with many vehicles involved. We show the applicability of our proposed safety time function based on the assessed communication quality for IEEE 802.11p-based V2X communication to meet safety constraints in dense vehicular traffic. © 2021 Institute of Electrical and Electronics Engineers Inc.. All rights reserved.

  • 16.
    Thunberg, Johan
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Lyamin, Nikita
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Sjöberg, Katrin
    Scania, Södertälje, Sweden.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES). Department of Electrical Engineering, Western Norway University of Applied Sciences, Bergen, Norway.
    Vehicle-to-Vehicle Communications for Platooning: Safety Analysis2019Ingår i: IEEE Networking Letters, ISSN 2576-3156, Vol. 1, nr 4, s. 168-172Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Vehicle-to-vehicle (V2V) communication is the key technology enabling platooning. This paper proposes an analytical framework that combines the characteristics of V2V communication (packet loss probabilities and packet transmission delays) with the physical mobility characteristics of vehicles (speed, distance between vehicles and their brake capacities). First, we present the feasible region of communications delays which guarantees safe emergency braking in platooning scenarios. Second, we derive a bound on the probability of safe braking. The presented framework is applied to understand the performance of the state-of-the-art V2V communication protocol for platooning.

  • 17.
    Thunberg, Johan
    et al.
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Luxembourg.
    Markdahl, Johan
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Luxembourg.
    Bernard, Florian
    Max-Planck-Institute for Informatics, Saarland Informatics Campus, Germany.
    Goncalves, Jorge
    Systems Biomedicine, University of Luxembourg, Luxembourg.
    A lifting method for analyzing distributed synchronization on the unit sphere2018Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 96, s. 253-258Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper introduces a new lifting method for analyzing convergence of continuous-time distributed synchronization/consensus systems on the unit sphere. Points on the d-dimensional unit sphere are lifted to the (d+1)-dimensional Euclidean space. The consensus protocol on the unit sphere is the classical one, where agents move toward weighted averages of their neighbors in their respective tangent planes. Only local and relative state information is used. The directed interaction graph topologies are allowed to switch as a function of time. The dynamics of the lifted variables are governed by a nonlinear consensus protocol for which the weights contain ratios of the norms of state variables. We generalize previous convergence results for hemispheres. For a large class of consensus protocols defined for switching uniformly quasi-strongly connected time-varying graphs, we show that the consensus manifold is uniformly asymptotically stable relative to closed balls contained in a hemisphere. Compared to earlier projection based approaches used in this context such as the gnomonic projection, which is defined for hemispheres only, the lifting method applies globally. With that, the hope is that this method can be useful for future investigations on global convergence.

  • 18.
    Thunberg, Johan
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Markdahl, Johan
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Luxembourg.
    Goncalves, Jorge
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Luxembourg.
    Dynamic controllers for column synchronization of rotation matrices: A QR-factorization approach2018Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 93, s. 20-25Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the multi-agent systems setting, this paper addresses continuous-time distributed synchronization of columns of rotation matrices. More precisely, k specific columns shall be synchronized and only the corresponding k columns of the relative rotations between the agents are assumed to be available for the control design. When one specific column is considered, the problem is equivalent to synchronization on the (d−1)-dimensional unit sphere and when all the columns are considered, the problem is equivalent to synchronization on SO(d). We design dynamic control laws for these synchronization problems. The control laws are based on the introduction of auxiliary variables in combination with a QR-factorization approach. The benefit of this QR-factorization approach is that we can decouple the dynamics for the k columns from the remaining d−k ones. Under the control scheme, the closed loop system achieves almost global convergence to synchronization for quasi-strong interaction graph topologies.

  • 19.
    Thunberg, Johan
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Saeed, Taqwa
    Lund University, Lund, Sweden.
    Sidorenko, Galina
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Valle, Felipe
    Högskolan i Halmstad, Akademin för informationsteknologi.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi. Karlsruhe Institute Of Technology, Karlsruhe, Germany.
    Cooperative Vehicles versus Non-Cooperative Traffic Light: Safe and Efficient Passing2023Ingår i: Computers, E-ISSN 2073-431X, Vol. 12, nr 8, artikel-id 154Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Connected and automated vehicles (CAVs) will be a key component of future cooperative intelligent transportation systems (C-ITS). Since the adoption of C-ITS is not foreseen to happen instantly, not all of its elements are going to be connected at the early deployment stages. We consider a scenario where vehicles approaching a traffic light are connected to each other, but the traffic light itself is not cooperative. Information about indented trajectories such as decisions on how and when to accelerate, decelerate and stop, is communicated among the vehicles involved. We provide an optimization-based procedure for efficient and safe passing of traffic lights (or other temporary road blockage) using vehicle-to-vehicle communication (V2V). We locally optimize objectives that promote efficiency such as less deceleration and larger minimum velocity, while maintaining safety in terms of no collisions. The procedure is computationally efficient as it mainly involves a gradient decent algorithm for one single parameter. © 2023 by the authors.

  • 20.
    Thunberg, Johan
    et al.
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Sidorenko, Galina
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Sjöberg, Katrin
    Scania CV AB, Södertälje, Sweden.
    Vinel, Alexey
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS). Western Norway University of Applied Sciences, Bergen, Norway.
    Efficiently Bounding the Probabilities of Vehicle Collision at Intelligent Intersections2021Ingår i: IEEE Open Journal of Intelligent Transportation Systems, E-ISSN 2687-7813, Vol. 2, s. 47-59Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Intelligent intersections have the potential to serve as an integral part of tomorrow’s traffic infrastructure. Wireless communication is key to enabling such technology. We consider a scenario where two flows of vehicles are to traverse an intelligent intersection. We investigate safety in emergency braking scenarios, where one of the vehicles in a flow suddenly decides to emergency brake and emergency braking messages are broadcast to affected vehicles. We provide a framework for computing lower bounds on probabilities for safe braking – collisions between vehicles are to be avoided. If we require that a crash or collision, for example, occurs at most once in a million scenarios, our approach allows for computation of lower bounds on the time-varying (or distance-varying) packet loss probabilities to ensure this. One of the benefits of the proposed framework is that the computational time is reduced; eliminating, for example, the need for time-consuming Monte Carlo simulations.

  • 21.
    Wei, Jieqiang
    et al.
    ACCESS Linnaeus Centre School of Electrical Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Zhang, Silun
    School of Engineering Sciences, KTH Royal Institute of Technology, Stockholm, Sweden..
    Adaldo, Antonio
    ACCESS Linnaeus Centre School of Electrical Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi. Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Luxembourg.
    Hu, Xiaoming
    Division of Optimization and Systems Theory Department of Mathematics, KTH Royal Institute of Technology, Stockholm, Sweden.
    Johansson, Karl Henrik
    ACCESS Linnaeus Centre School of Electrical Engineering, KTH Royal Institute of Technology, Stockholm, Sweden.
    Finite-Time Attitude Synchronization With Distributed Discontinuous Protocols2018Ingår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 63, nr 10, s. 3608-3615Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The finite-time attitude synchronization problem is considered in this paper, where the rotation of each rigid body is expressed using the axis-angle representation. Two discontinuous and distributed controllers using the vectorized signum function are proposed, which guarantee almost global and local convergence, respectively. Filippov solutions and nonsmooth analysis techniques are adopted to handle the discontinuities. Sufficient conditions are provided to guarantee finite-time convergence and boundedness of the solutions. Simulation examples are provided to verify the performances of the control protocols designed in this paper. 

  • 22.
    Yue, Zuogong
    et al.
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg; University New Soutch Wales, Sydney, NSW, Australia.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi. Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg.
    Gonçalves, Jorge
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Esch-sur-Alzette, Luxembourg.
    Network Stability, Realisation and Random Model Generation2019Ingår i: 2019 IEEE 58th Conference on Decision and Control (CDC), New York, NY: IEEE, 2019, s. 4539-4544Konferensbidrag (Refereegranskat)
    Abstract [en]

    Dynamical structure functions (DSFs) provide means for modelling networked dynamical systems and exploring interactive structures thereof. There have been several studies on methods/algorithms for reconstructing (Boolean) networks from time-series data. However, there are no methods currently available for random generation of DSF models with complex network structures for benchmarking. In particular, it may be desirable to generate stable DSF models or require the presence of feedback structures while keeping topology and dynamics random up to these constraints. This work provides procedures to obtain such models. On the path of doing so, we first study essential properties and concepts of DSF models, including realisation and stability. Then, the paper suggests model generation algorithms, whose implementations are now publicly available. © 2019 IEEE.

  • 23.
    Yue, Zuogong
    et al.
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Belvaux, Luxembourg.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS), Centrum för forskning om inbyggda system (CERES).
    Ljung, Lennart
    Department of Electrical Engineering, Linköping University, Linköping, Sweden.
    Yuan, Ye
    School of Artificial Intelligence and Automation, Huazhong University of Science and Technology, Wuhan, China.
    Goncalves, Jorge
    Luxembourg Centre for Systems Biomedicine, University of Luxembourg, Belvaux, Luxembourg.
    System Aliasing in Dynamic Network Reconstruction: Issues on Low Sampling Frequencies2021Ingår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 66, nr 12, s. 5788-5801Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Network reconstruction of dynamical continuous-time (CT) systems is motivated by applications in many fields. Due to experimental limitations, especially in biology, data can be sampled at low frequencies, leading to significant challenges in network inference. We introduce the concept of "system aliasing" and characterize the minimal sampling frequency that allows reconstruction of CT systems from low sampled data. A test criterion is also proposed to detect the presence of system aliasing. With no system aliasing, the paper provides an algorithm to reconstruct dynamic networks from full-state measurements in the presence of noise. With system aliasing, we add additional prior information such as sparsity to overcome the lack of identifiability. This paper opens new directions in modelling of network systems where samples have significant costs. Such tools are essential to process available data in applications subject to experimental limitations. © 2020, IEEE

  • 24.
    Yue, Zuogong
    et al.
    University of Luxembourg, Esch-sur-Alzette, Luxembourg.
    Thunberg, Johan
    Högskolan i Halmstad, Akademin för informationsteknologi, Halmstad Embedded and Intelligent Systems Research (EIS).
    Pan, Wei
    Department of Cognitive Robotics, TU Delft, Delft, Netherlands.
    Ljung, Lennart
    Linköpings universitet, Linkoping, Sweden.
    Gonçalves, Jorge
    University of Luxembourg, Esch-sur-Alzette, Luxembourg; University of Cambridge, Cambridge, United Kingdom.
    Dynamic network reconstruction from heterogeneous datasets2021Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 123, artikel-id 109339Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Performing multiple experiments is common when learning internal mechanisms of complex systems. These experiments can include perturbations of parameters or external disturbances. A challenging problem is to efficiently incorporate all collected data simultaneously to infer the underlying dynamic network. This paper addresses the reconstruction of dynamic networks from heterogeneous datasets under the assumption that the underlying networks share the same Boolean structure across all experiments. Parametric models are derived for dynamical structure functions, which describe causal interactions between measured variables. Multiple datasets are integrated into one regression problem with additional demands on group sparsity to assure network sparsity and structure consistency. To acquire structured group sparsity, we propose a sampling-based method, together with extended versions of l1-methods and sparse Bayesian learning. The performance of the proposed methods is benchmarked in numerical simulation. In summary, this paper presents efficient methods on network reconstruction from multiple experiments, and reveals practical experience that could guide applications. © 2020 Elsevier Ltd.

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