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  • 1.
    Andersen, Martin
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Rantzer, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Distributed Robust Stability Analysis of Interconnected Uncertain Systems2012Ingår i: Proceedings of the 51st IEEE Conference on Decision and Control, 2012, s. 1548-1553Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper considers robust stability analysis of a large network of interconnected uncertain systems. To avoid analyzing the entire network as a single large, lumped system, we model the network interconnections with integral quadratic constraints. This approach yields a sparse linear matrix inequality which can be decomposed into a set of smaller, coupled linear matrix inequalities. This allows us to solve the analysis problem efficiently and in a distributed manner. We also show that the decomposed problem is equivalent to the original robustness analysis problem, and hence our method does not introduce additional conservativeness.

  • 2.
    Andersen, Martin S.
    et al.
    Technical University of Denmark, Lyngby, Denmark.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Rantzer, Anders
    Lund University, Sweden.
    Robust stability analysis of sparsely interconnected uncertain systems2014Ingår i: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 59, nr 8, s. 2151-2156Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we consider robust stability analysis of large-scale sparsely interconnected uncertain systems. By modeling the interconnections among the subsystems with integral quadratic constraints, we show that robust stability analysis of such systems can be performed by solving a set of sparse linear matrix inequalities. We also show that a sparse formulation of the analysis problem is equivalent to the classical formulation of the robustness analysis problem and hence does not introduce any additional conservativeness. The sparse formulation of the analysis problem allows us to apply methods that rely on efficient sparse factorization techniques, and our numerical results illustrate the effectiveness of this approach compared to methods that are based on the standard formulation of the analysis problem.

    Ladda ner fulltext (pdf)
    fulltext
  • 3.
    Annergren, Mariette
    et al.
    KTH Royal Institute of Technology.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik.
    Wahlberg, Bo
    KTH Royal Institute of Technology.
    A Distributed Primal-dual Interior-point Method for Loosely Coupled Problems Using ADMMManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    In this paper we propose an efficient distributed algorithm for solving loosely coupled convex optimization problems. The algorithm is based on a primal-dual interior-point method in which we use the alternating direction method of multipliers (ADMM) to compute the primal-dual directions at each iteration of the method. This enables us to join the exceptional convergence properties of primal-dual interior-point methods with the remarkable parallelizability of ADMM. The resulting algorithm has superior computational properties with respect to ADMM directly applied to our problem. The amount of computations that needs to be conducted by each computing agent is far less. In particular, the updates for all variables can be expressed in closed form, irrespective of the type of optimization problem. The most expensive computational burden of the algorithm occur in the updates of the primal variables and can be precomputed in each iteration of the interior-point method. We verify and compare our method to ADMM in numerical experiments.

  • 4.
    Garulli, Andrea
    et al.
    University of Siena, Italy.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Masi, Alfio
    University of Siena, Italy.
    Wallin, Ragnar
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Robust Finite-Frequency H2 Analysis of Uncertain Systems2011Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In many applications, design or analysis is performed over a finite frequency range of interest. The importance of the H2/robust H2 norm highlights the necessity of computing this norm accordingly. This paper provides different methods for computing upper bounds on the robust finite-frequency H2 norm for systems with structured uncertainties. An application of the robust finite-frequency H2 norm for a comfort analysis problem of an aero-elastic model of an aircraft is also presented.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 5.
    Garulli, Andrea
    et al.
    Dipartimento di Ingegneria dell'Informazione Universita' degli Studi di Siena, Italy.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Masi, Alfio
    Dipartimento di Ingegneria dell'Informazione Universita' degli Studi di Siena, Italy.
    Wallin, Ragnar
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Robust finite-frequency H2 analysis of uncertain systems with application to flight comfort analysis2013Ingår i: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 21, nr 6, s. 887-897Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In many applications, design or analysis is performed over a finite-frequency range of interest. The importance of the H2 norm highlights the necessity of computing this norm accordingly. This paper provides different methods for computing upper bounds of the robust finite-frequency H2 norm for systems with structured uncertainties. An application of the robust finite-frequency H2 norm for a comfort analysis problem of an aero-elastic model of an aircraft is also presented.

    Ladda ner fulltext (pdf)
    fulltext
  • 6. Karami, Farzaneh
    et al.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Afshar, Ahmad
    Automated Model Generation for Analysis of Large-scale Interconnected Uncertain Systems2015Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The first challenge in robustness analysis of large-scale interconnected uncertain systems is to provide a model of such systems in a standard-form that is required within different analysis frameworks. This becomes particularly important for large-scale systems, as analysis tools that can handle such systems heavily rely on the special structure within such model descriptions. We here propose an automated framework for providing such models of large-scale interconnected uncertain systems that are used in Integral Quadratic Constraint (IQC) analysis. Specifically, in this paper we put forth a methodological way to provide such models from a block-diagram and nested description of interconnected uncertain systems. We describe the details of this automated framework using an example.

    Ladda ner fulltext (pdf)
    fulltext
  • 7.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Divide and Conquer: Distributed Optimization and Robustness Analysis2015Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    As control of large-scale complex systems has become more and more prevalent within control, so has the need for analyzing such controlled systems. This is particularly due to the fact that many of the control design approaches tend to neglect intricacies in such systems, e.g., uncertainties, time delays, nonlinearities, so as to simplify the design procedure.

    Robustness analysis techniques allow us to assess the effect of such neglected intricacies on performance and stability. Performing robustness analysis commonly requires solving an optimization problem. However, the number of variables of this optimization problem, and hence the computational time, scales badly with the dimension of the system. This limits our ability to analyze large-scale complex systems in a centralized manner. In addition, certain structural constraints, such as privacy requirements or geographical separation, can prevent us from even forming the analysis problem in a centralized manner.

    In this thesis, we address these issues by exploiting structures that are common in large-scale systems and/or their corresponding analysis problems. This enables us to reduce the computational cost of solving these problems both in a centralized and distributed manner. In order to facilitate distributed solutions, we employ or design tailored distributed optimization techniques. Particularly, we propose three distributed optimization algorithms for solving the analysis problem, which provide superior convergence and/or computational properties over existing algorithms. Furthermore, these algorithms can also be used for solving general loosely coupled optimization problems that appear in a variety of fields ranging from control, estimation and communication systems to supply chain management and economics.

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    fulltext
    Ladda ner (pdf)
    omslag
    Ladda ner (jpg)
    presentationsbild
  • 8.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Topics in Robustness Analysis2011Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis, we investigate two problems in robustness analysis of uncertain systems with structured uncertainty. The first problem concerns the robust finite frequency range H2 analysis of such systems. Classical robust H2 analysis methods are based on upper bounds for the robust H2 norm of a system which are computed over the whole frequency range. These bounds can be overly conservative, and therefore, classical robust H2 analysis methods can produce misleading results for finite frequency range analysis. In the first paper in the thesis, we address this issue by providing two methods for computing upper bounds for the robust finite-frequency H2 norm of the system. These methods utilize finitefrequency Gramians and frequency partitioning to calculate upper bounds for the robust finite-frequency H2 norm of uncertain systems with structured uncertainty. We show the effectiveness of these algorithms using both theoretical and practical experiments.

    Ladda ner fulltext (pdf)
    Topics in Robustness Analysis
    Ladda ner (pdf)
    omslag
  • 9.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Andersen, Martin S.
    Technical University of Denmark, Kongens Lyngby, Denmark.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Distributed solutions for loosely coupled feasibility problems using proximal splitting methods2015Ingår i: Optimization Methods and Software, ISSN 1055-6788, E-ISSN 1029-4937, Vol. 30, nr 1, s. 128-161Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we consider convex feasibility problems (CFPs) where the underlying sets are loosely coupled, and we propose several algorithms to solve such problems in a distributed manner. These algorithms are obtained by applying proximal splitting methods to convex minimization reformulations of CFPs. We also put forth distributed convergence tests which enable us to establish feasibility or infeasibility of the problem distributedly, and we provide convergence rate results. Under the assumption that the problem is feasible and boundedly linearly regular, these convergence results are given in terms of the distance of the iterates to the feasible set, which are similar to those of classical projection methods. In case the feasibility problem is infeasible, we provide convergence rate results that concern the convergence of certain error bounds.

    Ladda ner fulltext (pdf)
    fulltext
  • 10.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Andersen, Martin S.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Rantzer, Anders
    Lund University, Sweden.
    Decomposition and Projection Methods for Distributed Robustness Analysis of Interconnected Uncertain Systems2011Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We consider a class of convex feasibility problems where the constraints that describe the feasible set are loosely coupled. These problems arise in robust stability analysis of large, weakly interconnected systems. To facilitate distributed implementation of robust stability analysis of such systems, we propose two algorithms based on decomposition and simultaneous projections. The first algorithm is a nonlinear variant of Cimmino’s mean projection algorithm, but by taking the structure of the constraints into account, we can obtain a faster rate of convergence. The second algorithm is devised by applying the alternating direction method of multipliers to a convex minimization reformulation of the convex feasibility problem. We use numerical results to show that both algorithms require far less iterations than the accelerated nonlinear Cimmino algorithm.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 11.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Ankelhed, Daniel
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Project Report - ArduPilot2011Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Ardu software, for autopilot functionality has been used for several years for many different UAV platforms. The aim of this project is to use the same functionality for the plane platform existing in the department. Considering the mismatch of the existing platform with the previously used ones for Ardu autopilots it is of great importance to alter the software and hardware provided by Ardu in order to be able to fly the existing UAV.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 12.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Andersen, Martin S.
    Technical University of Denmark, Lyngby, Denmark.
    Distributed Interior-point Method for Loosely Coupled Problems2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we put forth distributed algorithms for solving loosely coupled unconstrained and constrained optimization problems. Such problems are usually solved using algorithms that are based on a combination of decomposition and first order methods. These algorithms are commonly very slow and require many iterations to converge. In order to alleviate this issue, we propose algorithms that combine the Newton and interior-point methods with proximal splitting methods for solving such problems. Particularly, the algorithm for solving unconstrained loosely coupled problems, is based on Newton's method and utilizes proximal splitting to distribute the computations for calculating the Newton step at each iteration. A combination of this algorithm and the interior-point method is then used to introduce a distributed algorithm for solving constrained loosely coupled problems. We also provide guidelines on how to implement the proposed methods efficiently and briefly discuss the properties of the resulting solutions.

  • 13.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Andersen, Martin S.
    University of California Los Angeles, USA.
    Rantzer, Anders
    Lund University, Sweden.
    Decomposition and Simultaneous Projection Methods for Convex Feasibility Problems with Application to robustness Analysis of Interconnected Uncertain Systems2011Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In this paper a specific class of convex feasibility problems are considered and tailored algorithms to solve this class of problems are introduced. First, the Nonlinear Cimmino Algorithm is reviewed. Then motivated by the special structure of the problems at hand, a modification to this method is proposed. Next, another method for solving the dual problem of the provided problem is presented. This leads to similar update rules for the variables as in the modified Nonlinear Cimmino Algorithm. Then an application for the proposed algorithms on the robust stability analysis of large scale weakly interconnected systems is presented and the performance of the proposed methods are compared.

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    FULLTEXT01
  • 14.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Andersen, Martin S.
    Technical University of Denmark, Lyngby, Denmark.
    Rantzer, Anders
    Lund University, Sweden.
    Distributed Robustness Analysis of Interconnected Uncertain Systems Using Chordal Decomposition2014Ingår i: Proceedings of the 19th IFAC World Congress, 2014 / [ed] Edward Boje and Xiaohua Xia, International Federation of Automatic Control , 2014, s. 2594-2599Konferensbidrag (Refereegranskat)
    Abstract [en]

    Large-scale interconnected uncertain systems commonly have large state and uncertainty dimensions. Aside from the heavy computational cost of solving centralized robust stability analysis techniques, privacy requirements in the network can also introduce further issues. In this paper, we utilize IQC analysis for analyzing large-scale interconnected uncertain systems and we evade these issues by describing a decomposition scheme that is based on the interconnection structure of the system. This scheme is based on the so-called chordal decomposition and does not add any conservativeness to the analysis approach. The decomposed problem can be solved using distributed computational algorithms without the need for a centralized computational unit. We further discuss the merits of the proposed analysis approach using a numerical experiment.

  • 15.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik.
    Andersen, Martin S.
    Technical University of Denmark.
    Rantzer, Anders
    Lund University.
    Distributed Semidefinite Programming with Application to Large-scale System AnalysisManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Distributed algorithms for solving coupled semidefinite programs (SDPs) commonly require manyiterations to converge. They also put high computational demand on the computational agents. In thispaper we show that in case the coupled problem has an inherent tree structure, it is possible to devisean efficient distributed algorithm for solving such problems. This algorithm can potentially enjoy thesame efficiency as centralized solvers that exploit sparsity. The proposed algorithm relies on predictorcorrectorprimal-dual interior-point methods, where we use a message-passing algorithm to compute thesearch directions distributedly. Message-passing here is closely related to dynamic programming overtrees. This allows us to compute the exact search directions in a finite number of steps. Furthermorethis number can be computed a priori and only depends on the coupling structure of the problem. Weuse the proposed algorithm for analyzing robustness of large-scale uncertain systems distributedly. Wetest the performance of this algorithm using numerical examples.

  • 16.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Garulli, Andrea
    University of Siena, Italy.
    On the Calculation of the Robust Finite Frequency H2 Norm2011Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The robust H2 norm plays an important role in analysis and design in many fields. However, for many practical applications, design and analysis is based on finite frequency range. In this paper we review the concept of the robust finite frequency H2 norm, and we provide an algorithmic method for calculating an upper bound for the mentioned quantity.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 17.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Garulli, Andrea
    University of Siena, Italy.
    On the Calculation of the Robust Finite Frequency H2 Norm2011Ingår i: Proceedings of the 18th IFAC World Congress, 2011, s. 3360-3365Konferensbidrag (Refereegranskat)
    Abstract [en]

    The robust H2 norm plays an important role in analysis and design in many fields. However, for many practical applications, design and analysis is based on finite frequency range. In this paper we review the concept of the robust finite frequency H2 norm, and we provide an algorithmic method for calculating an upper bound for the mentioned quantity.

  • 18.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Ohlsson, Henrik
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Ljung, Lennart
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Sparse Control Using Sum-of-norms Regularized Model Predictive Control2013Konferensbidrag (Refereegranskat)
    Ladda ner fulltext (pdf)
    fulltext
  • 19.
    Khoshfetrat Pakazad, Sina
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    S. Andersen, Martin
    Technical University of Denmark.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Rantzer, Anders
    Lund University.
    Decomposition and Projection Methods for Distributed Robustness Analysis of Interconnected Uncertain Systems2013Konferensbidrag (Refereegranskat)
    Abstract [en]

    We consider a class of convex feasibility problems where the constraints that describe the feasible set are loosely coupled. These problems arise in robust stability analysis of large, weakly interconnected uncertain systems. To facilitate distributed implementation of robust stability analysis of such systems, we describe two algorithms based on decomposition and simultaneous projections. The first algorithm is a nonlinear variant of Cimmino's mean projection algorithm, but by taking the structure of the constraints into account, we can obtain a faster rate of convergence. The second algorithm is devised by applying the alternating direction method of multipliers to a convex minimization reformulation of the convex feasibility problem. We use numerical results to show that both algorithms require far less iterations than the accelerated nonlinear Cimmino algorithm.

    Ladda ner fulltext (pdf)
    fulltext
  • 20.
    Kok, Manon
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Schön, Thomas
    Uppsala University, Sweden.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska fakulteten.
    Hol, Jeroen
    Xsens Technologies B.V., Enschede, Netherlands.
    A Scalable and Distributed Solution to the Inertial Motion Capture Problem2016Ingår i: Proceedings of the 19th International Conference on Information Fusion, Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 1348-1355Konferensbidrag (Refereegranskat)
    Abstract [en]

    In inertial motion capture, a multitude of body segments are equipped with inertial sensors, consisting of 3D accelerometers and 3D gyroscopes. Using an optimization-based approach to solve the motion capture problem allows for natural inclusion of biomechanical constraints and for modeling the connection of the body segments at the joint locations. The computational complexity of solving this problem grows both with the length of the data set and with the number of sensors and body segments considered. In this work, we present a scalable and distributed solution to this problem using tailored message passing, capable of exploiting the structure that is inherent in the problem. As a proof-of-concept we apply our algorithm to data from a lower body configuration. 

    Ladda ner fulltext (pdf)
    fulltext
  • 21.
    Ohlsson, Henrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Chen, Tianshi
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Ljung, Lennart
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Sastry, Shankar
    University of California at Berkeley, USA.
    Distributed Change Detection2012Ingår i: Proceedings of the 16th IFAC Symposium on System Identification, 2012, s. 77-82Konferensbidrag (Refereegranskat)
    Abstract [en]

    Change detection has traditionally been seen as a centralized problem. Many change detection problems are however distributed in nature and the need for distributed change detection algorithms is therefore significant. In this paper a distributed change detection algorithm is proposed. The change detection problem is first formulated as a convex optimization problem and then solved distributively with the alternating direction method of multipliers (ADMM). To further reduce the computational burden on each sensor, a homotopy solution is also derived. The proposed method have interesting connections with Lasso and compressed sensing and the theory developed for these methods are therefore directly applicable.

  • 22.
    Ohlsson, Henrik
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Chen, Tianshi
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Khoshfetratpakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Ljung, Lennart
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Sastry, S. Shankar
    University of Calif Berkeley, CA 94720 USA .
    Scalable anomaly detection in large homogeneous populations2014Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 50, nr 5, s. 1459-1465Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Anomaly detection in large populations is a challenging but highly relevant problem. It is essentially a multi-hypothesis problem, with a hypothesis for every division of the systems into normal and anomalous systems. The number of hypothesis grows rapidly with the number of systems and approximate solutions become a necessity for any problem of practical interest. In this paper we take an optimization approach to this multi-hypothesis problem. It is first shown to be equivalent to a non-convex combinatorial optimization problem and then is relaxed to a convex optimization problem that can be solved distributively on the systems and that stays computationally tractable as the number of systems increase. An interesting property of the proposed method is that it can under certain conditions be shown to give exactly the same result as the combinatorial multi-hypothesis problem and the relaxation is hence tight.

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  • 23.
    Wallin, Ragnar
    et al.
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Khoshfetrat Pakazad, Sina
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Hansson, Anders
    Linköpings universitet, Institutionen för systemteknik, Reglerteknik. Linköpings universitet, Tekniska högskolan.
    Garuli, Andrea
    Università di Siena, Italy.
    Masi, Alfio
    Università di Siena, Italy.
    Applications of IQC-Based Analysis Techniques for Clearance2012Ingår i: Optimization Based Clearance of Flight Control Laws: A Civil Aircraft Application / [ed] Andreas Varga, Anders Hansson and Guilhem Puyou, Springer Berlin/Heidelberg, 2012, s. 277-297Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    Results for stability analysis of the nonlinear rigid aircraft model and comfort and loads analysis of the integral aircraft model are presented in this chapter. The analysis is based on the theory for integral quadratic constraints and relies on linear fractional representations (LFRs) of the underlying closed-loop aircraft models. To alleviate the high computational demands associated with the usage of IQC based analysis to large order LFRs, two approaches have been employed aiming a trade-off between computational complexity and conservatism. First, the partitioning of the flight envelope in several smaller regions allows to use lower order LFRs in the analysis, and second, IQCs with lower computational demands have been used whenever possible. The obtained results illustrate the applicability of the IQCs based analysis techniques to solve highly complex analysis problems with an acceptable level of conservativeness.

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