Change search
Refine search result
1234567 51 - 100 of 518
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 51.
    Enqvist, Per
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Svensson, Göran
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Chat based contact center modeling system modeling, parameter estimation and missing data sampling2017In: ICORES 2017 - Proceedings of the 6th International Conference on Operations Research and Enterprise Systems, SciTePress , 2017, p. 464-469Conference paper (Refereed)
    Abstract [en]

    A Markovian system model for a contact center chat function is considered and partially validated. A hypothesis test on real chat data shows that it is reasonable to model the arrival process as a Poisson process. The arrival rate can be estimated using Maximum likelihood. The service process is more involved and the estimation of the service rate depends on the number of simultaneous chats handled by an agent. The estimation is made more difficult by the low level of detail in the given data-sets. A missing data approach with Gibbs sampling is used to obtain estimates for the service rates. Finally, we try to capture the generalized behaviour of the service-process and propose to use generalized functions to describe it when little information is available about the system at hand. 

  • 52. Dong, Yi
    et al.
    Xu, Shengyuan
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Coordinated control with multiple dynamic leaders for uncertain Lagrangian systems via self-tuning adaptive distributed observer2017In: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 27, no 16, p. 2708-2721Article in journal (Refereed)
    Abstract [en]

    This paper studies coordinated control of multiple Lagrangian systems with parametric uncertainties subject to external disturbances by proposing a fully distributed continuous control law based on the improved self-tuning adaptive observer inspired by non-identifier-based high-gain adaptive control technique. Under this distributed continuous control law, a group of Lagrangian systems are driven to the convex hull spanned by multiple heterogenous dynamic leaders, which can be any combination of step signals of arbitrary unknown magnitudes, ramp signals of arbitrary unknown slopes, and sinusoidal signals of arbitrary unknown amplitudes, initial phases, and any unknown frequencies. It is also worth to mention that this control law we propose, depending neither on any information of leader systems for uninformed followers, nor on external disturbances, even independent of neighbors' velocity, can achieve asymptotic tracking of multiple leaders without any additional condition instead of ensuring the ultimate boundedness of the containment error as in the literature.

  • 53. Yang, B.
    et al.
    He, H.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Detecting community structure in networks via consensus dynamics and spatial transformation2017In: Physica A: Statistical Mechanics and its Applications, ISSN 0378-4371, E-ISSN 1873-2119, Vol. 483, p. 156-170Article in journal (Refereed)
    Abstract [en]

    We present a novel clustering algorithm for community detection, based on the dynamics towards consensus and spatial transformation. The community detection problem is translated to a clustering problem in the N-dimensional Euclidean space by three stages: (1) the dynamics running on a network is emulated to a procedure of gas diffusion in a finite space; (2) the pressure distribution vectors are used to describe the influence that each node exerts on the whole network; (3) the similarity measures between two nodes are quantified in the N-dimensional Euclidean space by k-Nearest Neighbors method. After such steps, we could merge clusters according to their similarity distances and show the community structure of a network by a hierarchical clustering tree. Tests on several benchmark networks are presented and the results show the effectiveness and reliability of our algorithm.

  • 54. Dong, Yi
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed control of periodic formations for multiple under-actuated autonomous vehicles2017In: IET Control Theory & Applications, ISSN 1751-8644, E-ISSN 1751-8652, Vol. 11, no 1, p. 66-72Article in journal (Refereed)
    Abstract [en]

    One of the unique global behaviours of a group of under-actuated autonomous vehicles is known as cyclic pursue, which requires a group of vehicles to uniformly distribute on circles and at the same time, to orbit around a centre point, while circumnavigation further requires those vehicles to circumnavigate a predefined target of interest. Such behaviours can also be called periodic formations. This paper further studies the periodic formations for multi-agent systems composed of a group of under-actuated autonomous vehicles and a target of interest by proposing a distributed strategy to maintain any required distance between two vehicles and desired angle difference between vehicle's heading and the line of sight that takes directly towards its pursuing vehicle. The authors' distributed control law, dependent only on the information of its pursuing vehicle and itself, can not only enable a network of autonomous vehicles to circulate around a target of interest, but also achieve any physically feasible periodic formations, which include forming regular polygons as a special case.

  • 55. Liu, Z.
    et al.
    Wang, L.
    Wang, J.
    Dong, D.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Distributed sampled-data control of nonholonomic multi-robot systems with proximity networks2017In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 77, p. 170-179Article in journal (Refereed)
    Abstract [en]

    This paper considers the distributed sampled-data control problem of a group of mobile robots connected via distance-induced proximity networks. A dwell time is assumed in order to avoid chattering in the neighbor relations that may be caused by abrupt changes of positions when updating information from neighbors. Distributed sampled-data control laws are designed based on nearest neighbor rules, which in conjunction with continuous-time dynamics results in hybrid closed-loop systems. For uniform and independent initial states, a sufficient condition is provided to guarantee synchronization for the system without leaders. In order to steer all robots to move with the desired orientation and speed, we then introduce a number of leaders into the system, and quantitatively establish the proportion of leaders needed to track either constant or time-varying signals. All these conditions depend only on the neighborhood radius, the maximum initial moving speed and the dwell time, without assuming a prior properties of the neighbor graphs as are used in most of the existing literature.

  • 56.
    Engberg, Lovisa
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Forsgren, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Eriksson, Kjell
    Hardemark, Bjorn
    Explicit optimization of plan quality measures in intensity-modulated radiation therapy treatment planning2017In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 44, no 6, p. 2045-2053Article in journal (Refereed)
    Abstract [en]

    Purpose: To formulate convex planning objectives of treatment plan multicriteria optimization with explicit relationships to the dose-volume histogram (DVH) statistics used in plan quality evaluation. Methods: Conventional planning objectives are designed to minimize the violation of DVH statistics thresholds using penalty functions. Although successful in guiding the DVH curve towards these thresholds, conventional planning objectives offer limited control of the individual points on the DVH curve (doses-at-volume) used to evaluate plan quality. In this study, we abandon the usual penalty-function framework and propose planning objectives that more closely relate to DVH statistics. The proposed planning objectives are based on mean-tail-dose, resulting in convex optimization. We also demonstrate how to adapt a standard optimization method to the proposed formulation in order to obtain a substantial reduction in computational cost. Results: We investigated the potential of the proposed planning objectives as tools for optimizing DVH statistics through juxtaposition with the conventional planning objectives on two patient cases. Sets of treatment plans with differently balanced planning objectives were generated using either the proposed or the conventional approach. Dominance in the sense of better distributed doses-at-volume was observed in plans optimized within the proposed framework. Conclusion: The initial computational study indicates that the DVH statistics are better optimized and more efficiently balanced using the proposed planning objectives than using the conventional approach.

  • 57.
    Wei, Jieqiang
    et al.
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Zhang, Silun
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Adaldo, Antonio
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Finite-time attitude synchronization with a discontinuous protocol2017In: 13th IEEE International Conference on Control and Automation, ICCA 2017, IEEE Computer Society, 2017, p. 192-197, article id 8003058Conference paper (Refereed)
    Abstract [en]

    A finite-time attitude synchronization problem is considered in this paper where the rotation of each rigid body is expressed using the axis-angle representation. One simple discontinuous and distributed controller using the vectorized signum function is proposed. This controller only involves the sign of the state differences of adjacent neighbors. In order to avoid the singularity introduced by the axis-angular representation, an extra constraint is added to the initial condition. It is proved that for some initial conditions, the control law achieves finite-time attitude synchronization. One simulated example is provided to verify the usage of the control protocol designed in this paper.

  • 58.
    Ringh, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Karlsson, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. Shanghai Jiao Tong Univ, Dept Automat, Shanghai, Peoples R China; Shanghai Jiao Tong Univ, Sch Math, Shanghai, Peoples R China.
    Further results on multidimensional rational covariance extension with application to texture generation2017In: 2017 IEEE 56th Annual Conference on Decision and Control (CDC), IEEE , 2017Conference paper (Refereed)
    Abstract [en]

    The rational covariance extension problem is a moment problem with several important applications in systems and control as, for example, in identification, estimation, and signal analysis. Here we consider the multidimensional counterpart and present new results for the well-posedness of the problem. We apply the theory to texture generation by modeling the texture as the output of a Wiener system. The static nonlinearity in the Wiener system is assumed to be a thresholding function and we identify both the linear dynamical system and the thresholding parameter.

  • 59.
    Karlsson, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Ringh, Axel
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Generalized Sinkhorn Iterations for Regularizing Inverse Problems Using Optimal Mass Transport2017In: SIAM Journal on Imaging Sciences, ISSN 1936-4954, E-ISSN 1936-4954, Vol. 10, no 4, p. 1935-1962Article in journal (Refereed)
    Abstract [en]

    The optimal mass transport problem gives a geometric framework for optimal allocation and has recently attracted significant interest in application areas such as signal processing, image processing, and computer vision. Even though it can be formulated as a linear programming problem, it is in many cases intractable for large problems due to the vast number of variables. A recent development addressing this builds on an approximation with an entropic barrier term and solves the resulting optimization problem using Sinkhorn iterations. In this work we extend this methodology to a class of inverse problems. In particular we show that Sinkhorn-type iterations can be used to compute the proximal operator of the transport problem for large problems. A splitting framework is then used to solve inverse problems where the optimal mass transport cost is used for incorporating a priori information. We illustrate this method on problems in computerized tomography. In particular we consider a limited-angle computerized tomography problem, where a priori information is used to compensate for missing measurements.

  • 60.
    Ringh, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Zhuge, X.
    Palenstijn, W. J.
    Batenburg, K. J.
    Öktem, Ozan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    High-level algorithm prototyping: An example extending the TVR-DART algorithm2017In: Discrete Geometry for Computer Imagery: 20th IAPR International Conference, DGCI 2017, Vienna, Austria, September 19 – 21, 2017, Proceedings, Springer, 2017, p. 109-121Chapter in book (Refereed)
    Abstract [en]

    Operator Discretization Library (ODL) is an open-source Python library for prototyping reconstruction methods for inverse problems, and ASTRA is a high-performance Matlab/Python toolbox for large-scale tomographic reconstruction. The paper demonstrates the feasibility of combining ODL with ASTRA to prototype complex reconstruction methods for discrete tomography. As a case in point, we consider the total-variation regularized discrete algebraic reconstruction technique (TVR-DART). TVR-DART assumes that the object to be imaged consists of a limited number of distinct materials. The ODL/ASTRA implementation of this algorithm makes use of standardized building blocks, that can be combined in a plug-and-play manner. Thus, this implementation of TVR-DART can easily be adapted to account for application specific aspects, such as various noise statistics that come with different imaging modalities.

  • 61. Fontan, Angela
    et al.
    Shi, Guodong
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Altafini, Claudio
    Interval Consensus: a novel class of constrained consensus problems for multiagent networks2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, IEEE , 2017, p. 4155-4160Conference paper (Refereed)
    Abstract [en]

    In the consensus problem considered in this paper, each agent can impose a lower and an upper bound on the achievable consensus values. We show that if such state constraints are implemented by saturating the value transmitted to the neighboring nodes, the resulting constrained consensus problem must converge to the intersection of the intervals imposed by the individual agents.

  • 62.
    Zhang, Silun
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. Harbin Inst Technol, Control & Simulat Ctr, Harbin 150001, Heilongjiang, Peoples R China.
    He, Fenghua
    Hong, Yiguang
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Intrinsic Formation Control of Regular Polyhedra for Reduced Attitudes2017In: 2017 IEEE 56th Annual Conference on Decision and Control, CDC 2017, IEEE , 2017, p. 1002-1007Conference paper (Refereed)
    Abstract [en]

    This paper addresses formation control of reduced attitudes in which a continuous protocol is proposed for achieving and stabilizing all regular polyhedra (also known as Platonic solids) under a unified framework. The protocol contains only relative reduced attitude measurements and does not depend on any particular parametrization as is usually used in the literature. A key feature of the control proposed is that it is intrinsic in the sense that it does not need to incorporate any information of the desired formation. Instead, the achieved formation pattern is totally attributed to the geometric properties of the space and the designed inter-agent connection topology. Using a novel coordinates transformation, asymptotic stability of the desired formations is proven by studying stability of a constrained nonlinear system. In addition, a methodology to investigate stability of such constrained systems is also presented.

  • 63.
    Song, Wenjun
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Markdahl, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Zhang, Silun
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hong, Yiguang
    Intrinsic reduced attitude formation with ring inter-agent graph2017In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 85, p. 193-201Article in journal (Refereed)
    Abstract [en]

    This paper investigates the reduced attitude formation control problem for a group of rigid-body agents using feedback based on relative attitude information. Under both undirected and directed cycle graph topologies, it is shown that reversing the sign of a classic consensus protocol yields asymptotical convergence to formations whose shape depends on the parity of the group size. Specifically, in the case of even parity the reduced attitudes converge asymptotically to a pair of antipodal points and distribute equidistantly on a great circle in the case of odd parity. Moreover, when the inter-agent graph is an undirected ring, the desired formation is shown to be achieved from almost all initial states.

  • 64.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Kalman's Influence on My Scientific Work: Some Recollections and Reflections2017In: IEEE CONTROL SYSTEMS MAGAZINE, ISSN 1066-033X, Vol. 37, no 2, p. 156-157Article in journal (Refereed)
    Abstract [en]

    I first met Rudolf Kalman in Vienna, Austria, in the spring of 1972. I had recently finished my Ph.D. at the Royal Institute of Technology, Stockholm, Sweden, and I was invited to give a talk on my recent results in stochastic control theory at a small workshop that Kalman also attended. Apparently, Kalman was favorably impressed with my talk because he took me out for dinner the same evening and immediately invited me to come to Florida for the coming academic year. Kalman had just moved from Stanford to the University of Florida, and this is how I became his first postdoctoral associate at his new Center for Mathematical Systems Theory in the fall of 1972.

  • 65. Georgiou, Tryphon T.
    et al.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Likelihood Analysis of Power Spectra and Generalized Moment Problems2017In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, no 9, p. 4580-4592Article in journal (Refereed)
    Abstract [en]

    We develop an approach to the spectral estimation that has been advocated by [ A. Ferrante et al., "Time and spectral domain relative entropy: A new approach to multivariate spectral estimation,"IEEE Trans. Autom. Control, vol. 57, no. 10, pp. 2561-2575, Oct. 2012.] and, in the context of the scalar-valued covariance extension problem, by [P. Enqvist and J. Karlsson, "Minimal itakurasaito distance and covariance interpolation," in Proc. 47th IEEE Conf. Decision Control, 2008, pp. 137-142]. The aim is to determine the power spectrum that is consistent with given moments and minimizes the relative entropy between the probability law of the underlying Gaussian stochastic process to that of a prior. The approach is analogous to the framework of earlier work by Byrnes, Georgiou, and Lindquist and can also be viewed as a generalization of the classical work by Burg and Jaynes on the maximum entropy method. In this paper, we present a new fast algorithm in the general case (i.e., for general Gaussian priors) and show that for priors with a specific structure the solution can be given in closed form.

  • 66. Thunberg, Johan
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Goncalves, Jorge
    Local Lyapunov Functions for Consensus in Switching Nonlinear Systems2017In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 62, no 12, p. 6466-6472Article in journal (Refereed)
    Abstract [en]

    This note presents two theorems on asymptotic state consensus of continuous time nonlinear multi-agent systems. The agents reside in Rm and have switching interconnection topologies. Both the first theorem, formulated in terms of the states of individual agents, and the second theorem, formulated in terms of the pairwise states for pairs of agents, can be interpreted as variants of Lyapunov's second method. The two theorems complement each other; the second provides stronger convergence results under weaker graph topology assumptions, whereas the first often can be applied in a wider context in terms of the structure of the right-hand sides of the systems. The second theorem also sheds some new light on well-known results for consensus of nonlinear systems where the right-hand sides of the agents' dynamics are convex combinations of directions to neighboring agents. For such systems, instead of proving consensus by using the theory of contracting convex sets, a local quadratic Lyapunov function can be used.

  • 67. Zhang, Jiangbo
    et al.
    Hong, Yiguang
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    MULTIAGENT OPINION DYNAMICS OF BOUNDED CONFIDENCE WITH NONLOCAL AGGREGATIVE INTERACTION2017In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 2017, no 55, p. -2573, article id 4Article in journal (Refereed)
    Abstract [en]

    In this paper, we propose nonlocal aggregative opinion interactions for a bounded-confidence opinion model to demonstrate the fluctuation mechanism, and then study this opinion fluctuation mechanism by both theoretical analyses and numerical simulations. In this proposed agent-based opinion model, there are stubborn agents and regular agents: while each stubborn agent never changes its opinion, a regular agent updates his/her opinion based on selected agents' opinion values and his/her confidence bound. At first, we show that the global fluctuation for opinions of regular agents occurs almost surely if and only if the confidence bound of regular agents is larger than a critical value. Next, we give an estimated probability bound of the local fluctuation for regular agent opinions when the confidence bound is sufficiently small. Finally, we provide upper and lower bounds on the fluctuation strength and the regular agent opinion mean in the case when the global fluctuation occurs almost surely.

  • 68.
    Bokrantz, Rasmus
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. RaySearch Laboratories, Sweden.
    Fredriksson, Albin
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. RaySearch Laboratories, Sweden.
    Necessary and sufficient conditions for Pareto efficiency in robust multiobjective optimization2017In: European Journal of Operational Research, ISSN 0377-2217, E-ISSN 1872-6860, Vol. 262, no 2, p. 682-692Article in journal (Refereed)
    Abstract [en]

    We provide necessary and sufficient conditions for robust efficiency (in the sense of Ehrgott et al., 2014) to multiobjective optimization problems that depend on uncertain parameters. These conditions state that a solution is robust efficient (under minimization) if it is optimal to a strongly increasing scalarizing function, and only if it is optimal to a strictly increasing scalarizing function. By counterexample, we show that the necessary condition cannot be strengthened to convex scalarizing functions, even for convex problems. We therefore define and characterize a subset of the robust efficient solutions for which an analogous necessary condition holds with respect to convex scalarizing functions. This result parallels the deterministic case where optimality to a convex and strictly increasing scalarizing function constitutes a necessary condition for efficiency. By a numerical example from the field of radiation therapy treatment plan optimization, we illustrate that the curvature of the scalarizing function influences the conservatism of an optimized solution in the uncertain case.

  • 69.
    Zhang, Han
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Optimal energy consensus control for linear multi-agent systems2017In: 2017 36th Chinese Control Conference, CCC, IEEE Computer Society, 2017, p. 2663-2668, article id 8027765Conference paper (Refereed)
    Abstract [en]

    In this paper, an optimal energy cost controller for linear multi-agent systems' consensus is proposed. It is assumed that the topology among the agents is fixed and the agents are connected through an edge-weighted graph. The controller only uses relative information between agents. Due to the difficulty of finding the controller gain, we focus on finding the optimal controller among a sub-family whose design is based on Algebraic Riccati Equation (ARE) and guarantee consensus. It is found that the energy cost for such controllers is bounded by an interval and hence we minimize the upper bound. To do that, the control gain and the edge weights are optimized separately. The control gain is optimized by choosing Q = 0 in the ARE; the edge weights are optimized under the assumption that there is limited communication resources in the network. Negative edge weights are allowed, and the problem is formulated as a Semi-definite Programming (SDP) problem. The controller coincides with the optimal control in [8] when the graph is complete. Furthermore, two sufficient conditions for the existence of negative optimal edge weights realization are given.

  • 70.
    Hagrot, Erika
    et al.
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Oddsdottir, Hildur Aesa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hosta, Joan Gonzalez
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Jacobsen, Elling W.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Chotteau, Veronique
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Poly-pathway model, a novel approach to simulate multiple metabolic states by reaction network-based model-Application to amino acid depletion in CHO cell culture2017In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 259, p. 235-247Article in journal (Refereed)
  • 71.
    Song, Wenjun
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Tang, Y.
    Hong, Y.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Relative attitude formation control of multi-agent systems2017In: International Journal of Robust and Nonlinear Control, ISSN 1049-8923, E-ISSN 1099-1239, Vol. 27, no 18, p. 4457-4477Article in journal (Refereed)
    Abstract [en]

    This paper investigates the relative attitude formation control problem for a group of rigid-body agents using relative attitude information on SO(3). On the basis of the gradient of a potential function, a family of distributed angular velocity control laws, which differ in the sense of a geodesic distance dependent function, is proposed. With directed and switching interaction topologies, the desired relative attitude formation is showed to be achieved asymptotically provided that the topology is jointly quasi-strongly connected. Moreover, several sufficient conditions for the desired formation to be achieved exponentially and almost globally are given. Additionally, numerical examples are provided to illustrate the effectiveness of the proposed distributed control laws.

  • 72.
    Zhang, Silun
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Relative Information Based Distributed Control for Intrinsic Formations of Reduced Attitudes2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This dissertation concerns the formation problems for multiple reduced attitudes, which are extensively utilized in many pointing applications and under-actuated scenarios for attitude maneuvers. In contrast to most existing methodologies on formation control, the proposed method does not need to contain any formation errors in the protocol. Instead, the constructed formation is attributed to geometric properties of the configuration space and the designed connection topology. We refer to this type of formation control as intrinsic formation control. Besides, the control protocols proposed in this work are designed directly in space S2, avoiding to use any attitude parameterisations. At last but not least, along the studies, some elementary tools for reduced attitudes control are developed.In paper A, a continuous control law is provided for a reduced attitude systems, by which a regular tetrahedron formation can achieve asymptotic stability under a quite large family of gain functions in the control. Then, with a further restriction on the control gain, almost global stability of the tetrahedron formation is also obtained. In this work, we introduce a novel coordinates transformation that represents the relative reduced attitudes be-tween the agents. The proposed method is an intrinsic formation control that does not need to involve any information of the desired formation before-hand. Another virtue of the method proposed is that only relative attitude measurement is required.Paper B further concerns the formation control of all regular polyhedral configurations (also called Platonic solids) for reduced attitudes. According to the symmetries possessed by regular polyhedra, a unified framework is proposed for their formations. Via using the coordinates transformation previously proposed, it is shown that the stability of the desired formations can be provided by stabilizing a constrained nonlinear system. Then, a methodology to investigate the stability of this type of constrained systems is also presented. Paper C considers the problem of tracking and encircling a moving target by agents in 3-dimensional space. By this work, we show that similar design techniques proposed for reduced attitudes formations can also be applied to the formation control for point mass systems. Therein, a group of agents are driven to some desired formation on a spherical surface and simultaneously keep the center of this spherical formation coinciding with the target to be tracked. By properly designing communication topology, the agents constitute a cyclic formation along the equator of an encircling sphere.

  • 73.
    Zhang, Silun
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. Harbin Institute of Technology, China.
    He, F.
    Yao, Y.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Spherical formation of regular tetrahedra2017In: 2017 36th Chinese Control Conference, CCC, IEEE Computer Society, 2017, p. 1317-1322, article id 8027533Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the problem of tracking and encircling a moving target by agents in the 3-dimensional space. Specifically, a group of agents are driven to a regular tetrahedron formation on a spherical surface and simultaneously keep the center of this spherical formation coinciding with the target to be tracked. In the proposed method, to avoid the singularity caused by spherical parameterisations in control, we directly consider the spherical formation in space S2. Besides, the protocol proposed does not contain any information of the desired formation beforehand. Rather the constructed formation pattern is attributed to the properties of space S2 and the inter-agent topology.

  • 74.
    Almeida, Diogo
    et al.
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL. KTH.
    Ambrus, Rares
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Caccamo, Sergio
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, perception and learning, RPL.
    Chen, Xi
    KTH.
    Cruciani, Silvia
    Pinto Basto De Carvalho, Joao F
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, perception and learning, RPL.
    Haustein, Joshua
    KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, perception and learning, RPL.
    Marzinotto, Alejandro
    KTH, School of Computer Science and Communication (CSC), Computer Vision and Active Perception, CVAP.
    Vina, Francisco
    KTH.
    Karayiannidis, Yannis
    KTH.
    Ögren, Petter
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Jensfelt, Patric
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Kragic, Danica
    KTH, School of Computer Science and Communication (CSC), Robotics, perception and learning, RPL.
    Team KTH’s Picking Solution for the Amazon Picking Challenge 20162017In: Warehouse Picking Automation Workshop 2017: Solutions, Experience, Learnings and Outlook of the Amazon Robotics Challenge, 2017Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    In this work we summarize the solution developed by Team KTH for the Amazon Picking Challenge 2016 in Leipzig, Germany. The competition simulated a warehouse automation scenario and it was divided in two tasks: a picking task where a robot picks items from a shelf and places them in a tote and a stowing task which is the inverse task where the robot picks items from a tote and places them in a shelf. We describe our approach to the problem starting from a high level overview of our system and later delving into details of our perception pipeline and our strategy for manipulation and grasping. The solution was implemented using a Baxter robot equipped with additional sensors.

  • 75.
    Böck, Michelle
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. RaySearch Labs AB, Sweden.
    Eriksson, Kjell
    Forsgren, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hardemark, Bjorn
    Toward robust adaptive radiation therapy strategies2017In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 44, no 6, p. 2054-2065Article in journal (Refereed)
    Abstract [en]

    Purpose: To set up a framework combining robust treatment planning with adaptive re-optimization in order to maintain high treatment quality, to respond to interfractional geometric variations and to identify those patients who will benefit the most from an adaptive fractionation schedule. Methods: The authors propose robust adaptive strategies based on stochastic minimax optimization for a series of simulated treatments on a one-dimensional patient phantom. The plan applied during the first fractions should be able to handle anticipated systematic and random errors. Information on the individual geometric variations is gathered at each fraction. At scheduled fractions, the impact of the measured errors on the delivered dose distribution is evaluated. For a patient having received a dose that does not satisfy specified plan quality criteria, the plan is re-optimized based on these individually measured errors. The re-optimized plan is then applied during subsequent fractions until a new scheduled adaptation becomes necessary. In this study, three different adaptive strategies are introduced and investigated. (a) In the first adaptive strategy, the measured systematic and random error scenarios and their assigned probabilities are updated to guide the robust re-optimization. (b) In the second strategy, the degree of conservativeness is adapted in response to the measured dose delivery errors. (c) In the third strategy, the uncertainty margins around the target are recalculated based on the measured errors. The simulated treatments are subjected to systematic and random errors that are either similar to the anticipated errors or unpredictably larger in order to critically evaluate the performance of these three adaptive strategies. Results: According to the simulations, robustly optimized treatment plans provide sufficient treatment quality for those treatment error scenarios similar to the anticipated error scenarios. Moreover, combining robust planning with adaptation leads to improved organ-at-risk protection. In case of unpredictably larger treatment errors, the first strategy in combination with at most weekly adaptation performs best at notably improving treatment quality in terms of target coverage and organ-at-risk protection in comparison with a non-adaptive approach and the other adaptive strategies. Conclusion: The authors present a framework that provides robust plan re-optimization or margin adaptation of a treatment plan in response to interfractional geometric errors throughout the fractionated treatment. According to the simulations, these robust adaptive treatment strategies are able to identify candidates for an adaptive treatment, thus giving the opportunity to provide individualized plans, and improve their treatment quality through adaptation. The simulated robust adaptive framework is a guide for further development of optimally controlled robust adaptive therapy models.

  • 76. Elvander, F.
    et al.
    Adalbjörnsson, S. I.
    Karlsson, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Jakobsson, A.
    Using optimal transport for estimating inharmonic pitch signals2017In: 2017 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), Institute of Electrical and Electronics Engineers (IEEE), 2017, p. 331-335, article id 7952172Conference paper (Refereed)
    Abstract [en]

    In this work, we propose a novel multi-pitch estimation technique that is robust with respect to the inharmonicity commonly occurring in many applications. The method does not require any a priori knowledge of the number of signal sources, the number of harmonics of each source, nor the structure or scope of any possibly occurring inharmonicity. Formulated as a minimum transport distance problem, the proposed method finds an estimate of the present pitches by mapping any found spectral line to the closest harmonic structure. The resulting optimization is a convex and highly tractable linear programming problem. The preferable performance of the proposed method is illustrated using both simulated and real audio signals.

  • 77.
    Markdahl, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Kragic, D.
    Karayiannidis, Y.
    A hybrid control approach to task priority based mobile manipulation2016In: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, p. 801-806Conference paper (Refereed)
    Abstract [en]

    This paper proposes a hybrid control approach to task priority based mobile manipulation. More specifically, it uses a hybrid systems framework to address the problem of end-effector path following for a manipulator attached to a nonholonomic mobile platform where the joints are subject to constraints and the inputs signals are required to be bounded. A switched control strategy allows the robot to avoid infeasible and singular joint configurations while executing a bounded pseudo-inverse based feedback control law. The resulting closed loop system stabilizes the desired path, has a dwell time in each mode, and only switches a finite number of times.

  • 78. Zheng, Tianyu
    et al.
    He, Fenghua
    Yao, Yu
    Qi, Hongsheng
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    A Singular Perturbation-based Design for the Integrated Guidance and Control2016In: 2016 AMERICAN CONTROL CONFERENCE (ACC), IEEE conference proceedings, 2016, p. 4287-4292Conference paper (Refereed)
    Abstract [en]

    This paper considers the guidance and control problem of a flight vehicle with a seeker installed on the side of its head for avoiding the aerodynamic heating. In order to guarantee the target remaining in the seeker's sight of view, the line of sight and the attitude of the flight vehicle should be under some constraints which cause coupling between the guidance and the attitude control. Therefore, the integrated guidance and control (IGC) is necessary. We first formulate the guidance and control problem of the interceptor into an IGC problem with constraints. Then, a singular perturbation-based design approach is proposed to decompose the IGC problem into the control design of the quasi-steady-state subsystem and the boundary-layer subsystem individually. The receding horizon control is applied in the control design for the two subsystems. Simulation results show the effectiveness of the proposed approach.

  • 79.
    Karlsson, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Enqvist, Per
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Gattami, A.
    Confidence assessment for spectral estimation based on estimated covariances2016In: ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 4343-4347Conference paper (Refereed)
    Abstract [en]

    In probability theory, time series analysis, and signal processing, many identification and estimation methods rely on covariance estimates as an intermediate statistics. Errors in estimated covariances propagate and degrade the quality of the estimation result. In particular, in large network systems where each system node of the network gather and pass on results, it is important to know the reliability of the information so that informed decisions can be made. In this work, we design confidence regions based on covariance estimates and study how these can be used for spectral estimation. In particular, we consider three different confidence regions based on sets of unitarily invariant matrices and bound the eigenvalue distribution based on three principles: uniform bounds; arithmetic and harmonic means; and the Marcenko-Pastur Law eigenvalue distribution for random matrices. Using these methodologies we robustly bound the energy in a selected frequency band, and compare the resulting spectral bound from the respective confidence regions.

  • 80. Thunberg, Johan
    et al.
    Goncalves, Jorge
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Consensus and formation control on SE (3) for switching topologies2016In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 66, p. 109-121Article in journal (Refereed)
    Abstract [en]

    This paper addresses the consensus problem and the formation problem on SE(3) in multi-agent systems with directed and switching interconnection topologies. Several control laws are introduced for the consensus problem. By a simple transformation, it is shown that the proposed control laws can be used for the formation problem. The design is first conducted on the kinematic level, where the velocities are the control laws. Then, for rigid bodies in space, the design is conducted on the dynamic level, where the torques and the forces are the control laws. On the kinematic level, first two control laws are introduced that explicitly use Euclidean transformations, then separate control laws are defined for the rotations and the translations. In the special case of purely rotational motion, the consensus problem is referred to as consensus on SO(3) or attitude synchronization. In this problem, for a broad class of local representations or parameterizations of SO(3), including the Axis-Angle Representation, the Rodrigues Parameters and the Modified Rodrigues Parameters, two types of control laws are presented that look structurally the same for any choice of local representation. For these two control laws we provide conditions on the initial rotations and the connectivity of the graph such that the system reaches consensus on SO(3). Among the contributions of this paper, there are conditions for when exponential rate of convergence occurs. A theorem is provided showing that for any choice of local representation for the rotations, there is a change of coordinates such that the transformed system has a well known structure.

  • 81. Li, Y.
    et al.
    Yao, Y.
    He, F.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Control algorithm design for tracking and interacting with a ground moving target using an aerial vehicle2016In: Proceedings of the 35th Chinese Control Conference 2016, IEEE Computer Society, 2016, Vol. 2016, p. 5726-5731, article id 7554251Conference paper (Refereed)
    Abstract [en]

    In this paper, a three-dimensional control problem is investigated in which an aerial vehicle equipped with a vision system is required to track and interact with a ground moving target. In order to guarantee the continuity of target observation, horizontal and vertical commands are designed separately under the constraints of the detection zone and vehicle dynamics. In order to realize a time-optimal trajectory as well as a smooth interaction with the target, a switched interaction algorithm is proposed, which combines an improved Rendezvous-Guidance (RG) algorithm and a Proportional Integral (PI) controller by the choice of a switching point. Moreover, simulation results are provided to demonstrate not only the effectiveness of the proposed algorithm, but also a high tolerance for detection and execution errors near the interaction point.

  • 82.
    Qi, Luyuan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Design of evacuation strategies with crowd density feedback2016In: Science China Information Sciences, ISSN 1674-733X, E-ISSN 1869-1919, Vol. 59, no 1, p. 1-11Article in journal (Refereed)
    Abstract [en]

    A second-order stochastic model describing a large scale crowd is formulated, and an efficient evacuation strategy for agents in complex surroundings is proposed and solved numerically. The method consists in reshaping the crowd contour by making use of the crowd density feedback that is commonly available from geolocation technologies, and Kantorovich distance is used to transport the current shape into the desired one. The availability of the crowd density enables to solve the otherwise challenging forward-backward problem. Using this approach, we demonstrate via numerical results that the crowd migrates through the complex environment as designed.

  • 83.
    Song, Wenjun
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Markdahl, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hong, Y.
    Distributed control for intrinsic reduced attitude formation with ring inter-agent graph2016In: Proceedings of the IEEE Conference on Decision and Control, IEEE conference proceedings, 2016, p. 5599-5604Conference paper (Refereed)
    Abstract [en]

    This paper investigates the reduced attitude formation control problem for a group of rigid-body agents using only relative attitude information. Under both undirected and directed ring inter-agent graph, it is shown that when reversing the sign of a classic consensus control, different formations depending on the parity of the group size are achieved asymptotically. Specifically, the reduced attitudes converge to a pair of antipodal points with even number of agents, and distribute uniformly on a great circle with odd number of agents. To show the effectiveness of the proposed control law, illustrative examples are provided.

  • 84. Cai, G. Q.
    et al.
    Qi, Luyuan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Effects of habitat complexity on stochastic nonlinear ecosystems2016In: International Journal of Dynamics and Control, ISSN 2195-268X, Vol. 4, no 3, p. 275-283Article in journal (Refereed)
    Abstract [en]

    The term “Habitat Complexity” is used to measure the coupling level between different species in an ecosystem. It plays an important role to an ecosystem in which two or more species are interacting with each other. In the present paper, effects of the habitat complexity on predator–prey ecosystems with or without noise disturbances are investigated. Stochastic analysis methods of the Ito differential equations, the stochastic averaging method, and the Monte Carlo simulation are applied to obtain the stationary probability densities of the predator and prey population densities. It is found that the effects of the habitat complexity on the system dynamical behaviors are quite different for the deterministic case and the stochastic case. In absence of the noises, there are two bifurcation points dividing the level of habitat complexity into three regions: weak, moderate and strong. In the three regions, limit cycles, co-existing equilibrium states, and predator-extinct equilibrium states are present, respectively. In the stochastic case, the stable invariant measures in terms of probability distributions replace both the limit cycles and coexisting equilibriums in the regions of weak and moderate habitat complexity. For the case of strong habitat complexity, although the predator remains extinct, the prey is not in an equilibrium state, but possesses a probability distribution.

  • 85.
    Markdahl, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Exact Solutions to a Class of Feedback Systems on SO(n)2016In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 63, p. 138-147Article in journal (Refereed)
    Abstract [en]

    This paper provides a novel approach to the problem of attitude tracking for a class of almost globally asymptotically stable feedback laws on SO(n). The closed-loop systems are solved exactly for the rotation matrices as explicit functions of time, the initial conditions, and the gain parameters of the control laws. The exact solutions provide insight into the transient dynamics of the system and can be used to prove almost global attractiveness of the identity matrix. Applications of these results are found in model predictive control problems where detailed insight into the transient attitude dynamics is utilized to approximately complete a task of secondary importance. Knowledge of the future trajectory of the states can also be used as an alternative to the zero-order hold in systems where the attitude is sampled at discrete time instances.

  • 86. He, He
    et al.
    Yang, Bo
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Exploring community structure in networks by consensus dynamics2016In: Physica A: Statistical Mechanics and its Applications, ISSN 0378-4371, E-ISSN 1873-2119, Vol. 450, p. 342-353Article in journal (Refereed)
    Abstract [en]

    This paper investigates the relationship between community structure and consensus dynamics in complex networks. We analyze the dynamical process towards consensus and show that those sets of densely interconnected nodes corresponding to well-defined communities appear in different time scales. In order to reveal such topological scales, two algorithms built around the idea of visualizing the evolution of different measured quantities are proposed. Then we test our algorithms on a few benchmark graphs whose community structures are already known. Numeric simulations are given to demonstrate the effectiveness and reliability of our methods.

  • 87. Dong, Y.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Leader-following formation control problem of unicycles2016In: Proceedings of the 35th Chinese Control Conference 2016, IEEE Computer Society, 2016, p. 8154-8159, article id 7554654Conference paper (Refereed)
    Abstract [en]

    This paper proposes a distributed strategy to solve the leader-following formation problem for multiple under-actuated unicycles. Our distributed control law, dependent on the relative information of its nearest neighbor and itself, can not only enable a network of autonomous mobile agents to circulate around a target of interest, but also achieve any physically feasible formation.

  • 88.
    Ringh, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karlsson, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. Shanghai Jiao Tong Univ, Dept Automat & Math, Shanghai 200240, Peoples R China..
    MULTIDIMENSIONAL RATIONAL COVARIANCE EXTENSION WITH APPLICATIONS TO SPECTRAL ESTIMATION AND IMAGE COMPRESSION2016In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 54, no 4, p. 1950-1982Article in journal (Refereed)
    Abstract [en]

    The rational covariance extension problem (RCEP) is an important problem in systems and control occurring in such diverse fields as control, estimation, system identification, and signal and image processing, leading to many fundamental theoretical questions. In fact, this inverse problem is a key component in many identification and signal processing techniques and plays a fundamental role in prediction, analysis, and modeling of systems and signals. It is well known that the RCEP can be reformulated as a (truncated) trigonometric moment problem subject to a rationality condition. In this paper we consider the more general multidimensional trigonometric moment problem with a similar rationality constraint. This generalization creates many interesting new mathematical questions and also provides new insights into the original one-dimensional problem. A key concept in this approach is the complete smooth parameterization of all solutions, allowing solutions to be tuned to satisfy additional design specifications without violating the complexity constraints. As an illustration of the potential of this approach we apply our results to multidimensional spectral estimation and image compression. This is just a first step in this direction, and we expect that more elaborate tuning strategies will enhance our procedures in the future.

  • 89. Wang, J.
    et al.
    Zhang, P.
    Liu, Z.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Observer-based leader-following tracking control under both fixed and switching topologies2016In: Control Theory and Technology, ISSN 2095-6983, Vol. 14, no 1, p. 28-38Article in journal (Refereed)
    Abstract [en]

    This paper studies the tracking problem for a class of leader-follower multi-agent systems moving on the plane using observer-based cooperative control strategies. In our set-up, only a subset of the followers can obtain some relative information on the leader. We assume that the control input of the leader is not known to any of the followers while the system matrix is broadcast to all the followers. To track such a leader, an observer-based decentralized feedback controller is designed for each follower and detailed analysis for the convergence is presented for both fixed and switching interaction topologies between agents with the method of common Lyapunov function. We can also generalize the result to the higher dimension case for fixed topology and some special system matrices of the leader for switching topology.

  • 90. Thunberg, J.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Optimal output consensus for linear systems: A topology free approach2016In: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 68, p. 352-356Article in journal (Refereed)
    Abstract [en]

    In this paper, for any homogeneous system of agents with linear continuous time dynamics, we formulate an optimal control problem. In this problem a convex cost functional of the control signals of the agents shall be minimized, while the outputs of the agents shall coincide at some given finite time. This is an instance of the rendezvous or finite time consensus problem. We solve this problem without any constraints on the communication topology and provide a solution as an explicit feedback control law for the case when the dynamics of the agents is output controllable. It turns out that the communication graph topology induced by the solution is complete. Based on this solution for the finite time consensus problem, we provide a solution to the case of infinite time horizon. Furthermore, we investigate under what circumstances it is possible to express the controller as a feedback control law of the output instead of the states.

  • 91.
    Hagrot, Erika
    et al.
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Oddsdóttir, Hildur Aesa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hosta, Joan Gonzalez
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Jacobsen, Elling W.
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Chotteau, Veronique
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Poly-pathway model, a novel approach to simulate multiple metabolic states by reaction network-based model - Application to amino acid depletion in CHO cell culture2016In: Journal of Biotechnology, ISSN 0168-1656, E-ISSN 1873-4863, Vol. 228, p. 37-49Article in journal (Refereed)
    Abstract [en]

    Mammalian cell lines are characterized by a complex and flexible metabolism. A single model that could describe the variations in metabolic behavior triggered by variations in the culture conditions would be a precious tool in bioprocess development. In this paper, we introduce an approach to generate a poly-pathway model and use it to simulate diverse metabolic states triggered in response to removal, reduction or doubling of amino acids in the culture medium of an antibody-producing CHO cell line. Macro-reactions were obtained from a metabolic network via elementary flux mode enumeration and the fluxes were modeled by kinetic equations with saturation and inhibition effects from external medium components. Importantly, one set of kinetic parameters was estimated using experimental data of the multiple metabolic states. A good fit between the model and the data was obtained for the majority of the metabolites and the experimentally observed flux variations. We find that the poly-pathway modeling approach is promising for the simulation of multiple metabolic states.

  • 92.
    Forsgren, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Gill, Philip E.
    Wong, Elizabeth
    Primal and dual active-set methods for convex quadratic programming2016In: Mathematical programming, ISSN 0025-5610, E-ISSN 1436-4646, Vol. 159, no 1-2, p. 469-508Article in journal (Refereed)
    Abstract [en]

    Computational methods are proposed for solving a convex quadratic program (QP). Active-set methods are defined for a particular primal and dual formulation of a QP with general equality constraints and simple lower bounds on the variables. In the first part of the paper, two methods are proposed, one primal and one dual. These methods generate a sequence of iterates that are feasible with respect to the equality constraints associated with the optimality conditions of the primal-dual form. The primal method maintains feasibility of the primal inequalities while driving the infeasibilities of the dual inequalities to zero. The dual method maintains feasibility of the dual inequalities while moving to satisfy the primal inequalities. In each of these methods, the search directions satisfy a KKT system of equations formed from Hessian and constraint components associated with an appropriate column basis. The composition of the basis is specified by an active-set strategy that guarantees the nonsingularity of each set of KKT equations. Each of the proposed methods is a conventional active-set method in the sense that an initial primal- or dual-feasible point is required. In the second part of the paper, it is shown how the quadratic program may be solved as a coupled pair of primal and dual quadratic programs created from the original by simultaneously shifting the simple-bound constraints and adding a penalty term to the objective function. Any conventional column basis may be made optimal for such a primal-dual pair of shifted-penalized problems. The shifts are then updated using the solution of either the primal or the dual shifted problem. An obvious application of this approach is to solve a shifted dual QP to define an initial feasible point for the primal (or vice versa). The computational performance of each of the proposed methods is evaluated on a set of convex problems from the CUTEst test collection.

  • 93.
    Oddsdottir, Hildur Aesa
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Hagrot, Erika
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Chotteau, Veronique
    KTH, School of Biotechnology (BIO), Industrial Biotechnology.
    Forsgren, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Robustness analysis of elementary flux modes generated by column generation2016In: Mathematical Biosciences, ISSN 0025-5564, E-ISSN 1879-3134, Vol. 273, p. 45-56Article in journal (Refereed)
    Abstract [en]

    Elementary flux modes (EFMs) are vectors defined from a metabolic reaction network, giving the connections between substrates and products. EFMs-based metabolic flux analysis (MFA) estimates the flux over each EFM from external flux measurements through least-squares data fitting. The measurements used in the data fitting are subject to errors. A robust optimization problem includes information on errors and gives a way to examine the sensitivity of the solution of the EFMs-based MFA to these errors. In general, formulating a robust optimization problem may make the problem significantly harder. We show that in the case of the EFMs-based MFA, when the errors are only in measurements and bounded by an interval, the robust problem can be stated as a convex quadratic programming (QP) problem. We have previously shown how the data fitting problem may be solved in a column-generation framework. In this paper, we show how column generation may be applied also to the robust problem, thereby avoiding explicit enumeration of EFMs. Furthermore, the option to indicate intervals on metabolites that are not measured is introduced in this column generation framework. The robustness of the data is evaluated in a case-study, which indicates that the solutions of our non-robust problems are in fact near-optimal also when robustness is considered, implying that the errors in measurement do not have a large impact on the optimal solution. Furthermore, we showed that the addition of intervals on unmeasured metabolites resulted in a change in the optimal solution.

  • 94.
    Yang, Yuecheng
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Self-organization and Intervention of Nonlinear Multi-agent Systems2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This dissertation concerns the self-organization behaviors in different types of multi-agent systems, and possible ways to apply interventions on top ofthat to achieve certain goals. A bounded confidence opinion dynamics modelis considered for the first two papers. Theoretical analysis of the model isperformed and modifications of the model are given so that it will have better properties in some aspect. Leader-follower based models are studied in the third to fifth papers where various optimal control problems are considered. Different methods such as Pontryagin minimum principle and dynamic programming are used to solve those optimal control problem. For complex problems, one may only get approximate solutions or suboptimal solutions.In Paper A and Paper B, we consider the continuous-time Hegselmann-Krause (H-K) model and its variations and target the problem of reaching consensus. A sufficient condition on the initial opinion distribution is givento guarantee consensus for the original continuous-time H-K model. A modified model is provided and proven to be able to lead a larger range of initial opinions to synchronization. An H-K model with an exo-system is also studied where sufficient conditions on the exo-system are given for the purpose of consensus.In Paper C and Paper D, optimal control problems with leader-followerbased multi-agent systems are discussed. Analytic solutions are derived if the dynamics is linear by applying Pontryagin minimum principle. For generalnon-linear leader-follower interactions, we provide a method that use sstatistic moments of the follower crowd to approximate the optimal control.The dynamic programming approach is used and certain approximation ofthe Hamilton-Jacobi-Bellman equations is needed. The computational burdenis so heavy that model predictive control method is required in practical applications.In Paper E, we apply a similar method to the approach used in PaperD to target a pollutant elimination problem. It implies that we can use themethod to attack optimal control problem with partial differential equation constraints by discretization in space. The dimension of the discretization is not related to the computational complexity since only the statistic moments are needed.

  • 95.
    Zhang, Silun
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Song, Wenjun
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    He, Fenghua
    Control and Simulation Center, Harbin Institute of Technology, 150001, China.
    Yao, Yu
    Control and Simulation Center, Harbin Institute of Technology, 150001, China.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Spherical cyclic formation control2016In: Proceedings of the 35th Chinese Control Conference 2016, IEEE Computer Society, 2016, Vol. 2016, p. 8207-8212, article id 7554663Conference paper (Refereed)
    Abstract [en]

    In this paper, we study the problem of tracking and encircling a moving target by agents in 3D. Specifically, a group of agents are driven to some desired formation on a spherical surface and simultaneously keep the center of this spherical formation coinciding with the target to be tracked. In our control design, the desired formation is not used as a reference signal for tracking. Rather by designing communication topology for the agents we can achieve the desired formation using relative positions only. We can also place the desired cyclic formation on the equator if the north pole is specified.

  • 96.
    Ringh, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karlsson, Johan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. Shanghai Jiao Tong University, China.
    The Multidimensional Circulant Rational Covariance Extension Problem: Solutions and Applications in Image Compression2016In: 2015 54th IEEE Conference on Decision and Control (CDC), 2015, Institute of Electrical and Electronics Engineers (IEEE), 2016, p. 5320-5327Conference paper (Refereed)
    Abstract [en]

    Rational functions play a fundamental role in systems engineering for modelling, identification, and control applications. In this paper we extend the framework by Lindquist and Picci for obtaining such models from the circulant trigonometric moment problems, from the one-dimensional to the multidimensional setting in the sense that the spectrum domain is multidimensional. We consider solutions to weighted entropy functionals, and show that all rational solutions of certain bounded degree can be characterized by these. We also consider identification of spectra based on simultaneous covariance and cepstral matching, and apply this theory for image compression. This provides an approximation procedure for moment problems where the moment integral is over a multidimensional domain, and is also a step towards a realization theory for random fields.

  • 97.
    Karlsson, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. Shanghai Jiao Tong University, China.
    Ringh, Axel
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    The Multidimensional Moment Problem with Complexity Constraint2016In: Integral equations and operator theory, ISSN 0378-620X, E-ISSN 1420-8989, Vol. 84, no 3, p. 395-418Article in journal (Refereed)
    Abstract [en]

    A long series of previous papers have been devoted to the (one-dimensional) moment problem with nonnegative rational measure. The rationality assumption is a complexity constraint motivated by applications where a parameterization of the solution set in terms of a bounded finite number of parameters is required. In this paper we provide a complete solution of the multidimensional moment problem with a complexity constraint also allowing for solutions that require a singular measure added to the rational, absolutely continuous one. Such solutions occur on the boundary of a certain convex cone of solutions. In this paper we provide complete parameterizations of all such solutions. We also provide errata for a previous paper in this journal coauthored by one of the authors of the present paper.

  • 98.
    Svärd, Henrik
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    A branch and bound algorithm for evaluation of the Findley fatigue criterion2015In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 73, p. 27-38Article in journal (Refereed)
    Abstract [en]

    In this manuscript, a new algorithm for evaluation of the Findley fatigue criterion is proposed. The algorithm uses a branch and bound technique to limit the number of investigated planes in the search for the critical one. The algorithm has two major advantages over currently existing methods. Firstly, for a given tolerance on the error of the evaluation, it needs to investigate fewer planes on average, thereby reducing the execution time compared to state of the art methods. Secondly, the algorithm is guaranteed to give results within a tolerance of the global maximum, and this tolerance may be freely chosen by the analyst.

  • 99.
    Ringh, Axel
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karlsson, Johan Mikael
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    A fast solver for the circulant rational covariance extension problem2015In: 2015 European Control Conference, ECC 2015, Institute of Electrical and Electronics Engineers (IEEE), 2015, p. 727-733Conference paper (Refereed)
    Abstract [en]

    The rational covariance extension problem is to parametrize the family of rational spectra of bounded degree that matches a given set of covariances. This article treats a circulant version of this problem, where the underlying process is periodic and we seek a spectrum that also matches a set of given cepstral coefficients. The interest in the circulant problem stems partly from the fact that this problem is a natural approximation of the non-periodic problem, but is also a tool in itself for analysing periodic processes. We develop a fast Newton algorithm for computing the solution utilizing the structure of the Hessian. This is done by extending a current algorithm for Toeplitz-plus-Hankel systems to the block-Toeplitz-plus-block-Hankel case. We use this algorithm to reduce the computational complexity of the Newton search from O(n3) to O(n2), where n corresponds to the number of covariances and cepstral coefficients.

  • 100. Hu, J.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Zhang, Y.
    Adaptive bipartite tracking control for coopetition networks2015In: 2015 34th Chinese Control Conference (CCC), IEEE Computer Society, 2015, p. 7067-7072, article id 7260757Conference paper (Refereed)
    Abstract [en]

    Cooperation and competition are two typical interactional relationships in natural and engineering networked systems. Some interesting collective behaviors can emerge through local interactions within the networked systems. This paper considers a bipartite consensus for a group of agents interacting both cooperatively and competitively. Meanwhile, the intrinsic nonlinear dynamics of all the agents are unknown for the neighboring agents. Thus, the interaction network, which we call a coopetition network, is firstly represented by a signed graph. Then, some adaptive estimate laws are proposed for the unknown dynamics. Finally, an adaptive tracking control is designed for each agent to reach a bipartite consensus on the state of the leader. Some sufficient conditions are derived for bipartite consensus of multi-agent systems with the help of a structural balance theory. Simulation results are provided to demonstrate the bipartite consensus formation.

1234567 51 - 100 of 518
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf