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  • 401.
    Fanizza, Giovanna
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    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.
    Nagamune, Ryozo
    A global analysis approach to passivity preserving model reduction2006In: Proceedings Of The 45th IEEE Conference On Decision And Control, Vols 1-14, 2006, p. 3399-3404Conference paper (Refereed)
    Abstract [en]

    Passivity-preserving model reduction for linear time-invariant systems amounts to approximating a positive-real rational transfer function with one of lower degree. Recently Antoulas and Sorensen have proposed such a model-reduction method based on Krylov projections. The method is based on an observation by Antoulas (in the single-input/single-output case) that if the approximant is preserving a subset of the spectral zeros and takes the same values as the original transfer function in the mirror points of the preserved spectral zeros, then the approximant is also positive real. However, this turns out to be a special solution in the theory of analytic interpolation with degree constraint developed by Byrnes, Georgiou and Lindquist, namely the maximum-entropy (central) solution. By tuning the interpolation points and the spectral zeros, as prescribed by this theory, one is able to obtain considerably better reduced-order models.

  • 402.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    A sector condition for local robustness of limit cycles2006In: 2006 American Control Conference, Vols 1-12, 2006, Vol. 1-12, p. 5014-5019Conference paper (Refereed)
    Abstract [en]

    Robustness of periodic oscillations in autonomous feedback systems are considered for systems with separable nonlinearities. Local quadratic separation of the nonlinear dynamics from the linear part of the dynamics is used to characterize a set of systems that exhibit periodic oscillation in a bounded frequency and amplitude range. The main analysis condition can be formulated as a feasibility problem for linear matrix inequalities.

  • 403.
    Hallander, Elin
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Gutman, Per-Olof
    Active damping of longitudinal oscillations in a wheel loader2006In: Computer Aided Control System Design, 2006, p. 1097-1102Conference paper (Refereed)
    Abstract [en]

    A simplified model of the longitudinal motion around a constant velocity trajectory of a wheel loader is developed, for the purpose of finding a control that actively damps oscillations in the acceleration, following an up shifting gear change. Measurements from different drivers and different gear changes indicate similar oscillation frequencies for the investigated vehicle. The model parameters and the gear change induced disturbance are adjusted so that the model output closely fits the true measurements of the vehicle acceleration after a gear change, in the investigated frequency band. With the engine as a torque actuator, active damping of the oscillations in the acceleration is investigated through simulations. The possible improvements using feedback from measured engine speed seem to be limited, while a predefined feed-forward programme shows promising results.

  • 404.
    Anisi, David A.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Adaptive node distribution for on-line trajectory planning2006In: ICAS-Secretariat - 25th Congress of the International Council of the Aeronautical Sciences 2006, Curran Associates, Inc., 2006, p. 3150-3157Conference paper (Refereed)
    Abstract [en]

    Direct methods for trajectory optimization are traditionally based on a priori temporal dis- cretization and collocation methods. In this work, the problem of node distribution is for- mulated as an optimization problem, which is to be included in the underlying non-linear mathematical programming problem (NLP). The benefits of utilizing the suggested method for on-line trajectory optimization are illustrated by a missile guidance example.

  • 405.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Analysis and design of oscillator networks2006In: 2006 Chinese Control Conference, Vols 1-5, 2006, p. 1319-1324Conference paper (Refereed)
    Abstract [en]

    The design and analysis of oscillator networks raises a number fundamental questions in systems and control. The existence, uniqueness, and location of periodic solutions of dynamical systems as well as the stability and robusmess of these solutions are all challenging problems that must be addressed in design and analysis of such networks. In this paper we investigate local stability and robustness properties of oscillator networks. The focus is on how the design of the network interconnection matrix affects both convergence and robustness of the network.

  • 406.
    Kuroiwa, Yohei
    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.
    Bi-tangential Nevanlinna-Pick interpolation with a complexity constraint2006In: Proceedings of the 17th International Symposium on the Mathematical Theory of Networks and Systems: Kyoto, 2006, 2006, p. 2541-2563Conference paper (Other academic)
  • 407.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Control of collective behavior for multi-robotic systems2006In: Proceedings of 2006 International Conference on Artificial Intelligence: 50 Years' Achievements, Future Directions And Social Impacts, 2006, p. PL23-PL23Conference paper (Refereed)
  • 408. Fujioka, H.
    et al.
    Almér, Stefan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Kao, C. -Y
    Control synthesis for a class of PWM systems for robust tracking and H ∞ performance2006In: Proc IEEE Conf Decis Control, 2006, p. 4861-4866Conference paper (Refereed)
    Abstract [en]

    Robust control with robust tracking is considered for a class of pulse-width modulated systems (PWM) that appear, for example, in power electronics applications. The control objective is to regulate a high frequency ripple signal to robustly track a constant reference signal in an average sense. To achieve this goal, a new H∞ -control problem with integral action and averaged sampling is proposed. The design procedure is verified on a synchronous buck converter.

  • 409. Larsson, Robin
    et al.
    Berge, Sten
    Bodin, Per
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Fuel efficient relative orbit control strategies for formation flying and rendezvous within PRISMA2006Conference paper (Refereed)
    Abstract [en]

    This article will outline the relative orbit control, including guidance and control tasks developed for the PRISMA technology in-orbit formation flying testbed mission. The focus is on real-time implementable solutions, working in arbitrary orbits (0 ≤ e < 1). The algorithms presented are based on linear Model Predictive Control(MPC). The computational heavy part of a MPC approach is usually to setup the matrices, associated with the linear program, if zero order hold discretization methods are used. This article introduces a different approach which uses the state transition matrices developed in [1], that accommodate steps of arbitrary length. This approach allows much larger time steps than the time varying dynamics would allow when zero order hold discretizing the dynamics. The computational complexity will instead depend on the number of state constraints and the number of allowed control inputs. These two factors can be designed to meet real-time execution requirements. The initial tests show that the expected ΔV consumption compares well to previous works in this area with only a small fraction of the computational load. To date, a version of the control algorithm for the Proximity Operations has been implemented and successfully demonstrated in real-time on flight representative hardware as a part of SSC's demonstration at the 6th International ESA Conference on Guidance, Navigation and Control Systems. The maximum processor load increase over one second was about 3%, on a Leon2 processor running at 32 MHz, with code not optimized for computational efficiency.

  • 410.
    Byrnes, Christopher
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Georgiou, T. T.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Megretski, A.
    Generalized interpolation in H-infinity with a complexity constraint2006In: Transactions of the American Mathematical Society, ISSN 0002-9947, E-ISSN 1088-6850, Vol. 358, no 3, p. 965-987Article in journal (Refereed)
    Abstract [en]

    In a seminal paper, Sarason generalized some classical interpolation problems for H-infinity functions on the unit disc to problems concerning lifting onto H-2 of an operator T that is defined on K=H-2 circle minus phi H-2 (phi is an inner function) and commutes with the (compressed) shift S. In particular, he showed that interpolants (i.e., f is an element of H-infinity such that f(S)=T) having norm equal to parallel to T parallel to exist, and that in certain cases such an f is unique and can be expressed as a fraction f=b/a with a, b is an element of K. In this paper, we study interpolants that are such fractions of K functions and are bounded in norm by 1 (assuming that parallel to T parallel to<1, in which case they always exist). We parameterize the collection of all such pairs (a, b)is an element of K x K and show that each interpolant of this type can be determined as the unique minimum of a convex functional. Our motivation stems from the relevance of classical interpolation to circuit theory, systems theory, and signal processing, where phi is typically a finite Blaschke product, and where the quotient representation is a physically meaningful complexity constraint.

  • 411.
    Werme, Mats
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Globally optimal benchmark solutions to some small-scale discretized continuum topology optimization problems2006In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 32, no 3, p. 259-262Article in journal (Refereed)
    Abstract [en]

    In this note, globally optimal solutions to three sets of small-scale discretized continuum topology optimization problems are presented. All the problems were discretized by the use of nine-node isoparametric finite elements. The idea is that these solutions can be used as benchmark problems when testing new algorithms for finding pure 0-1 solutions to topology optimization problems defined on discretized ground structures.

  • 412.
    Almér, Stefan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Harmonic Lyapunov functions in the analysis of periodically switched systems2006In: PROCEEDINGS OF THE 45TH IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-14, 2006, p. 2759-2764Conference paper (Refereed)
    Abstract [en]

    The dynamic phasor model of a time-periodic system is used to derive a stability test involving a harmonic Lyapunov function. This reveals a new interpretation of the harmonic Lyapunov function with an appealing time-domain representation. Most importantly, it indicates that the ideas behind the harmonic Lyapunov equation can be generalized to include cyclic switching systems that have different pulse form in each period.

  • 413.
    Carlsson, Fredrik
    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.
    Iterative regularization in intensity-modulated radiation therapy optimization2006In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 33, no 1, p. 225-234Article in journal (Refereed)
    Abstract [en]

    A common way to solve intensity-modulated radiation therapy (IMRT) optimization problems is to use a beamlet-based approach. The approach is usually employed in a three-step manner: first a beamlet-weight optimization problem is solved, then the fluence profiles are converted into stepand-shoot segments, and finally postoptimization of the segment weights is performed. A drawback of beamlet-based approaches is that beamlet-weight optimization problems are ill-conditioned and have to be regularized in order to produce smooth fluence profiles that are suitable for conversion. The purpose of this paper is twofold: first, to explain the suitability of solving beamlet-based IMRT problems by a BFGS quasi-Newton sequential quadratic programming method with diagonal initial Hessian estimate, and second, to empirically show that beamlet-weight optimization problems should be solved in relatively few iterations when using this optimization method. The explanation of the suitability is based on viewing the optimization method as an iterative regularization method. In iterative regularization, the optimization problem is solved approximately by iterating long enough to obtain a solution close to the optimal one, but terminating before too much noise occurs. Iterative regularization requires an optimization method that initially proceeds in smooth directions and makes rapid initial progress. Solving ten beamlet-based IMRT problems with dose-volume objectives and bounds on the beamlet-weights, we find that the considered optimization method fulfills the requirements for performing iterative regularization. After segment-weight optimization, the treatments obtained using 35 beamlet-weight iterations outperform the treatments obtained using 100 beamlet-weight iterations, both in terms of objective value and of target uniformity. We conclude that iterating too long may in fact deteriorate the quality of the deliverable plan.

  • 414. Baratchart, L.
    et al.
    Enqvist, Per
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Gombani, A.
    Olivi, M.
    Minimal symmetric Darlington synthesis: A frequency domain approach2006In: Proc IEEE Conf Decis Control, 2006, p. 6732-6737Conference paper (Refereed)
    Abstract [en]

    Given a p × p Schur function S, we consider the problem of constructing a symmetric Darlington synthesis of minimal size. This amounts essentially to finding a stable all-pass square extension of S of minimal size. The characterization is done in terms of the multiplicities of the zeros. As a special case we obtain conditions for symmetric Darlington synthesis to be possible without increasing the McMillan degree for a symmetric rational contractive matrix which is strictly contractive in the right half-plane. This technique immediately extends to the case where, allowing for a higher dimension of the extension, we require no increase in the McMillan degree. Also in this case we obtain sharper results than those existing in the literature (see [1]).

  • 415.
    Bortolin, Gianantonio
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Gutman, P O
    Nilsson, B
    On modelling of curl in multi-ply paperboard2006In: Journal of Process Control, ISSN 0959-1524, E-ISSN 1873-2771, Vol. 16, no 4, p. 419-429Article in journal (Refereed)
    Abstract [en]

    This paper describes a grey-box model for the curl and twist of the carton board produced at AssiDoman Frovi, Sweden. The main equations are based on classical lamination theory of composite materials, and each constituent ply is considered as a macroscopic homogeneous, elastic medium. The model used data from June to September 2004, and shows a general agreement between predicted and measured curvatures. The data were cleaned from outliers by means of the Hampel filter, a nonlinear moving window filter, and with a model based method. Regularization and backwards elimination were used to cope with the low identifiability of the problem. The model was then complemented with a sub-model of immeasurable/unmodelled disturbances estimated with an extended Kalman filter. (C) 2005 Elsevier Ltd. All rights reserved.

  • 416.
    Enqvist, Per
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    On the simultaneous realization problem - Markov-parameter and covariance interpolation2006In: Signal Processing, ISSN 0165-1684, E-ISSN 1872-7557, Vol. 86, no 10, p. 3043-3054Article in journal (Refereed)
    Abstract [en]

    An efficient algorithm for determining the unique minimal and stable realization of a window of Markov parameters and covariances is derived. The main difference compared to the Q-Markov COVER theory is that here we let the variance of the input noise be a variable, thus avoiding a certain data consistency criterion. First, it is shown that maximizing the input variance of the realization over all interpolants yields a minimal degree solution-a result closely related to maximum entropy. Secondly, the state space approach of the Q-Markov COVER theory is used for analyzing the stability and structure of the realization by straightforward application of familiar realization theory concepts, in particular the occurrence of singular spectral measures is characterized.

  • 417.
    Forsgren, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    On warm starts for interior methods2006In: System Modeling and Optimization / [ed] Ceragioli, F; Dontchev, A; Futura, H; Marti, K; Pandolfi, L, 2006, Vol. 199, p. 51-66Conference paper (Refereed)
    Abstract [en]

    An appealing feature of interior methods for linear programming is that the number of iterations required to solve a problem tends to be relatively insensitive to the choice of initial point. This feature has the drawback that it is difficult to design interior methods that efficiently utilize information from an optimal solution to a "nearby" problem. We discuss this feature in the context of general nonlinear programming and specialize to linear programming. We demonstrate that warm start for a particular nonlinear programming problem, given a near-optimal solution for a "nearby" problem, is closely related to an SQP method applied to an equality-constrained problem. These results are further refined for the case of linear programming.

  • 418.
    Anisi, David
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Robinson, John W.C.
    Swedish Defence Research Agency (FOI), Department of Aeronautics .
    Ögren, Petter
    Swedish Defence Research Agency (FOI).
    On-line Trajectory planning for aerial vehicles: a safe approach with guaranteed task completion2006In: Collection of Technical Papers: AIAA Guidance, Navigation, and Control Conference 2006, 2006, p. 914-938Conference paper (Refereed)
    Abstract [en]

    On-line trajectory optimization in three dimensional space is the main topic of the paper at hand. The high-level framework augments on-line receding horizon control with an off-line computed terminal cost that captures the global characteristics of the environment, as well as any possible mission objectives. The first part of the paper is devoted to the single vehicle case while the second part considers the problem of simultaneous arrival of multiple aerial vehicles. The main contribution of the first part is two-fold. Firstly, by augmenting a so called safety maneuver at the end of the planned trajectory, this paper extends previous results by addressing provable safety properties in a 3 D setting. Secondly, assuming initial feasibility, the planning method presented is shown to have finite time task completion. Moreover, a quantitative comparison between the two competing objectives of optimality and computational tractability is made. Finally, some other key characteristics of the trajectory planner, such as ability to minimize threat exposure and robustness, are highlighted through simulations. As for the simultaneous arrival problem considered in the second part, by using a time-scale separation principle, we are able to adopt standard Laplacian control to a consensus problem which is neither unconstrained, nor first order.

  • 419. Georgiou, Tryphon T.
    et al.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Remarks on control design with degree constraint2006In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 51, no 7, p. 1150-1156Article in journal (Refereed)
    Abstract [en]

    The purpose of this note is to highlight similarities and differences between two alternative methodologies for feedback control design under constraints on the McMillan degree of the feedback system. Both sets of techniques focus on uniformly optimal designs. The first is based on the work of Gahinet and Apkarian and that of Skelton et al., while the other is based on earlier joint work of the authors with C. I. Byrnes.

  • 420.
    Samuelsson, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Gustavi, Tove
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Karasalo, Maja
    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.
    Robust formation adaptation for mobile platforms with noisy sensor information2006In: 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems, Vols 1-12, NEW YORK: IEEE , 2006, p. 2527-2532Conference paper (Refereed)
    Abstract [en]

    In this paper stability and formation adaptation of mobile multi-agent systems with limited sensor information is studied. A globally stable control for line formations with varying separations and bearing angles between the agents is evaluated in simulations and experiments with Khepera. robots. The control algorithm only requires information available from on-board sensors, although stability is improved if communication and sharing of information between the agents is possible. In addition, the control only needs a coarse estimation of the actual target speed.

  • 421.
    Gustavi, Tove
    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.
    Robust formation adaptation for mobile robots2006In: 2006 IEEE/RSJ International Conference on Intelligent Robots and Systems, Vols 1-12, NEW YORK: IEEE , 2006, p. 2521-2526Conference paper (Refereed)
    Abstract [en]

    In this paper, formation adaptation and stability for mobile multi-agent systems is studied. The objective is to suggest a set of robust control functions that can be combined to build complex formations of mobile robots. A properly designed formation should be able to follow a single leader in a clustered environment and to, if necessary, adapt to the surroundings by changing its shape. The two control algorithms proposed here are adapted for systems with limited communication capacity and low performance sensors. The algorithms only require information that can be directly achieved from on-board sensors and, in particular, they only need very coarse estimation of the velocity of the neighbors in the formation. An arbitrary change of the shape of a formation may require switching between control algorithms. In the paper, it is shown that switching between the two proposed control algorithms is stable under some reasonable assumptions. The results are verified by simulations, which also show that switching can be performed safely even with a high noise level and no prior filtering of sensor input.

  • 422.
    Anisi, David A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Ögren, Petter
    Department of Autonomous Systems Swedish Defence Research Agency.
    Robinson, John W. C.
    Department of Autonomous Systems Swedish Defence Research Agency.
    Safe receding horizon control of an aerial vehicle2006In: PROCEEDINGS OF THE 45TH IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-14, IEEE , 2006, p. 57-62Conference paper (Refereed)
    Abstract [en]

    This paper addresses the problem of designing a real time high performance controller and trajectory generator for air vehicles. The control objective is to use information about terrain and enemy threats to fly low and avoid radar exposure on the way to a given target. The proposed algorithm builds on the well known approach of Receding Horizon Control (RHC) combined with a terminal cost, calculated from a graph representation of the environment. Using a novel safety maneuver, and under an assumption on the maximal terrain inclination, we are able to prove safety as well as task completion. The safety maneuver is incorporated in the short term optimization, which is performed using Nonlinear Programming (NLP). Some key characteristics of the trajectory planner are highlighted through simulations.

  • 423.
    Kuroiwa, Yohei
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Sensitivity shaping under degree constraint: Bi-tangential Nevanlinna-Pick interpolation with a complexity constraint approach2006In: Proceedings Of The 45th IEEE Conference On Decision And Control, Vols 1-14, 2006, p. 3542-3547Conference paper (Refereed)
    Abstract [en]

    A solution to the bi-tangential Nevanlinna-Pick interpolation with a complexity constraint is presented. The solution can be described by the ratio of functions, Psi Q(-1), similar to the previous works. It is obtained by minimizing a strictly convex functional. The essence in the present work lies in the construction of the domain of Q. The theory is applied to a sensitivity shaping problem, and a certain class of the free design parameter IF is suggested to obtain a controller of low degree.

  • 424.
    Enqvist, Per
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Spectrum estimation by interpolation of covariances and cepstrum parameters in an exponentional class of spectral densities2006Conference paper (Refereed)
    Abstract [en]

    Given output data of a stationary stochastic process estimates of the covariances and cepstrum parameters can be obtained. Methods of moments have been applied to these parameters for designing ARMA processes, and it has been shown that these two sets of parameters in fact form local coordinates for the set of ARMA processes, but that some combinations of cepstrum parameters and covariances cannot be matched exactly within this class of processes. Therefore, another class of processes is considered in this paper in order to be able to match any combination of covariances and cepstrum parameters. The main result is that a process with spectral density of the form Φ exP{Σ k=0mpk(zk + z-k)}/Σ k=0nqk(zk + z-k)/2 can always match given covariances and cepstrum parameters. This is proven using a fixed-point argument, and a non-linear least-squares problem is proposed for determining a solution.

  • 425. Iannelli, Luigi
    et al.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Vasca, Francesco
    Subtleties in the averaging of hybrid systems with application to power electronics2006In: 2nd IFAC Conference on Analysis and Design of Hybrid Systems, 2006 / [ed] C.G. Cassandras, A. Giua, C. Seatzu, J. Zaytoon, IFAC , 2006Conference paper (Refereed)
    Abstract [en]

    Dither signals are commonly used in electronics for implementing different type of modulations in power converters, which represent a very interesting class of hybrid systems. It was recently shown that a nonsmooth dithered system can be approximated by an averaged system provided that the dither frequency is sufficiently high and that the amplitude distribution function of the dither is absolutely continuous and has bounded derivative. This result is exploited in this paper for power converters. Averaged models corresponding to various shapes of dither signal are analyzed, showing that dither with Lipschitz continuous amplitude distribution function can be used to adapt the equivalent gain of the power converter.

    Download full text (pdf)
    dither_adh06
  • 426. Iannelli, Luigi
    et al.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Vasca, F.
    Subtleties in the averaging of hybrid systems with applications to power electronics2006In: Analysis and Design of Hybrid Systems 2006, Elsevier, 2006, p. 247-252Chapter in book (Other academic)
    Abstract [en]

    Dither signals are commonly used in electronics for implementing different type of modulations in power converters, which represent a very interesting class of hybrid systems. It was recently shown that a non-smooth dithered system can be approximated by an averaged system if the dither frequency is sufficiently high and that the amplitude distribution function of the dither is continuous and has bounded derivative. In power electronics, a large class of systems can be modeled as hybrid dynamical systems due to the presence of switching devices (for instance diodes or transistors) that "instantaneously" change the dynamical behavior of the system. This class of systems can be adequately represented by hybrid systems or nonlinear differential equations with discontinuous nonlinearities. One of the standard approaches for designing control algorithms for power converters is to use modulation schemes (e.g. pulse width modulation, PWM).

  • 427. Byrnes, Christopher I.
    et al.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    The generalized moment problem with complexity constraint2006In: Integral equations and operator theory, ISSN 0378-620X, E-ISSN 1420-8989, Vol. 56, no 2, p. 163-180Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a synthesis of our differentiable approach to the generalized moment problem, an approach which begins with a reformulation in terms of differential forms and which ultimately ends up with a canonically derived, strictly convex optimization problem. Engineering applications typically demand a solution that is the ratio of functions in certain finite dimensional vector space of functions, usually the same vector space that is prescribed in the generalized moment problem. Solutions of this type are hinted at in the classical text by Krein and Nudelman and stated in the vast generalization of interpolation problems by Sarason. In this paper, formulated as generalized moment problems with complexity constraint, we give a complete parameterization of such solutions, in harmony with the above mentioned results and the engineering applications. While our previously announced results required some differentiability hypotheses, this paper uses a weak form involving integrability and measurability hypotheses that are more in the spirit of the classical treatment of the generalized moment problem. Because of this generality, we can extend the existence and well-posedness of solutions to this problem to nonnegative, rather than positive, initial data in the complexity constraint. This has nontrivial implications in the engineering applications of this theory. We also extend this more general result to the case where the numerator can be an arbitrary positive absolutely integrable function that determines a unique denominator in this finite-dimensional vector space. Finally, we conclude with four examples illustrating our results.

  • 428.
    Karlsson, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM.
    Georgiou, Tryphon
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    The inverse problem of analytic interpolation with degree constraint2006In: Proceedings Of The 45th IEEE Conference On Decision And Control, Vols 1-14, 2006, p. 559-564Conference paper (Refereed)
    Abstract [en]

    In [7], (6] a theory for degree-constrained analytic interpolation was developed in terms of the minimizers of certain convex entropy functionals. In the present paper, we introduce and study relevant inverse problems. More specifically, we answer the following two questions. First, given a function f which satisfies specified interpolation conditions, when is it that f can be obtained as the minimizer of a suitably chosen entropy functional? Second, given a function g, when does there exist a suitably entropy functional so that the unique minitnizer f which is subject to interpolation constraints also satisfies vertical bar f vertical bar = vertical bar g vertical bar on the unit circle. The theory and answers to these questions suggest an approach to identifying interpolants of a given degree and of a given approximate shape.

  • 429.
    Svanberg, Krister
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Werme, Mats
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Topology optimization by a neighbourhood search method based on efficient sensitivity calculations2006In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 67, no 12, p. 1670-1699Article in journal (Refereed)
    Abstract [en]

    This paper deals with topology optimization of discretized load-carrying continuum structures, where the design of the structure is represented by binary design variables indicating material or void in the various finite elements. Efficient exact methods for discrete sensitivity calculations are developed. They utilize the fact that if just one or two binary variables are changed to their opposite binary values then the new stiffness matrix is essentially just a low-rank modification of the old stiffness matrix, even if some nodes in the structure may disappear or re-enter. As an application of these efficient sensitivity calculations, a new neighbourhood search method is presented, implemented, and applied on some test problems, one of them with 6912 nine-node finite elements where the von Mises stress in each non-void element is considered.

  • 430.
    Svanberg, Krister
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Werme, Mats
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Topology optimization by sequential integer linear programming2006In: IUTAM SYMPOSIUM ON TOPOLOGICAL DESIGN OPTIMIZATION OF STRUCTURES, MACHINES AND MATERIALS: STATUS AND PERSPECTIVES / [ed] Bendsoe, MP; Olhoff, N; Sigmund, O, DORDRECHT: SPRINGER , 2006, Vol. 137, p. 425-436Conference paper (Refereed)
    Abstract [en]

    We present a new iterative approach for topology optimization of load-carrying structures. In each iteration an integer linear programming problem is generated and solved. The method is guaranteed to find a local optimum of the original problem, but not necessarily a global optimum. Numerical results for some stress constrained problems are presented.

  • 431.
    Carlsson, Fredrik
    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.
    Rehbinder, Henrik
    RaySearch Labs.
    Eriksson, Kjell
    RaySearch Labs.
    Using eigenstructure of the Hessian to reduce the dimension of the intensity modulated radiation therapy optimization problem2006In: Annals of Operations Research, ISSN 0254-5330, E-ISSN 1572-9338, Vol. 148, no 1, p. 81-94Article in journal (Refereed)
    Abstract [en]

    Optimization is of vital importance when performing intensity modulated radiation therapy to treat cancer tumors. The optimization problem is typically large-scale with a nonlinear objective function and bounds on the variables, and we solve it using a quasi-Newton sequential quadratic programming method. This study investigates the effect on the optimal solution, and hence treatment outcome, when solving an approximate optimization problem of lower dimension. Through a spectral decompostion, eigenvectors and eigenvalues of an approximation to the Hessian are computed. An approximate optimization problem of reduced dimension is formulated by introducing eigenvector weights as optimization parameters, where only eigenvectors corresponding to large eigenvalues are included.

    The approach is evaluated on a clinical prostate case. Compared to bixel weight optimization, eigenvector weight optimization with few parameters results in faster initial decline in the objective function, but with inferior final solution. Another approach, which combines eigenvector weights and bixel weights as variables, gives lower final objective values than what bixel weight optimization does. However, this advantage comes at the expense of the pre-computational time for the spectral decomposition.

  • 432.
    Blomqvist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    A convex optimization approach to complexity constrained analytic interpolation with applications to ARMA estimation and robust control2005Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    Analytical interpolation theory has several applications in systems and control. In particular, solutions of low degree, or more generally of low complexity, are of special interest since they allow for synthesis of simpler systems. The study of degree constrained analytic interpolation was initialized in the early 80's and during the past decade it has had significant progress.

    This thesis contributes in three different aspects to complexity constrained analytic interpolation: theory, numerical algorithms, and design paradigms. The contributions are closely related; shortcomings of previous design paradigms motivate development of the theory, which in turn calls for new robust and efficient numerical algorithms.

    Mainly two theoretical developments are studied in the thesis. Firstly, the spectral Kullback-Leibler approximation formulation is merged with simultaneous cepstral and covariance interpolation. For this formulation, both uniqueness of the solution, as well as smoothness with respect to data, is proven. Secondly, the theory is generalized to matrix-valued interpolation, but then only allowing for covariance-type interpolation conditions. Again, uniqueness and smoothness with respect to data is proven.

    Three algorithms are presented. Firstly, a refinement of a previous algorithm allowing for multiple as well as matrix-valued interpolation in an optimization framework is presented. Secondly, an algorithm capable of solving the boundary case, that is, with spectral zeros on the unit circle, is given. This also yields an inherent numerical robustness. Thirdly, a new algorithm treating the problem with both cepstral and covariance conditions is presented.

    Two design paradigms have sprung out of the complexity constrained analytical interpolation theory. Firstly, in robust control it enables low degree Hinf controller design. This is illustrated by a low degree controller design for a benchmark problem in MIMO sensitivity shaping. Also, a user support for the tuning of controllers within the design paradigm for the SISO case is presented. Secondly, in ARMA estimation it provides unique model estimates, which depend smoothly on the data as well as enables frequency weighting. For AR estimation, a covariance extension approach to frequency weighting is discussed, and an example is given as an illustration. For ARMA estimation, simultaneous cepstral and covariance matching is generalized to include prefiltering. An example indicates that this might yield asymptotically efficient estimates.

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  • 433.
    Svanberg, Krister
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Werme, Mats
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    A hierarchical neighbourhood search method for topology optimization2005In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 29, no 5, p. 325-340Article in journal (Refereed)
    Abstract [en]

    This paper presents a hierarchical neighbourhood search method for solving topology optimization problems defined on discretized linearly elastic continuum structures. The design of the structure is represented by binary design variables indicating material or void in the various finite elements.

    Two different designs are called neighbours if they differ in only one single element, in which one of them has material while the other has void. The proposed neighbourhood search method repeatedly jumps to the "best" neighbour of the current design until a local optimum has been found, where no further improvement can be made. The "engine" of the method is an efficient exploitation of the fact that if only one element is changed (from material to void or from void to material) then the new global stiffness matrix is just a low-rank modification of the old one. To further speed up the process, the method is implemented in a hierarchical way. Starting from a coarse finite element mesh, the neighbourhood search is repeatedly applied on finer and finer meshes.

    Numerical results are presented for minimum-weight problems with constraints on respectively compliance, strain energy densities in all non-void elements, and von Mises stresses in all non-void elements.

  • 434.
    Byrnes, Christopher I.
    et al.
    Washington Univ, St Louis.
    Fanizza, Giovanna
    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.
    A homotopy continuation solution of the covariance extension equation2005In: Lecture notes in control and information sciences, ISSN 0170-8643, E-ISSN 1610-7411, Vol. 321, p. 27-42Article in journal (Refereed)
  • 435.
    Jönsson, Ulf T.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    A small-gain theory for limit cycles of systems on lure form2005In: SIAM Journal of Control and Optimization, ISSN 0363-0129, E-ISSN 1095-7138, Vol. 44, no 3, p. 909-938Article in journal (Refereed)
    Abstract [en]

    Local exponential stability and local robustness for limit cycle solutions of ordinary differential equations can be verified using the characteristic multipliers. These well-known results are here generalized to a class of infinite-dimensional systems. Stability and robustness are now verified using certain invertibility conditions on the linear equations that are obtained when the system is linearized along the limit cycle. The new criterion reduces to the classical condition on the characteristic multipliers when we consider a finite-dimensional system which is perturbed by a bounded but possibly infinite-dimensional operator. The computation of a robustness margin, i.e., a bound on the maximally allowed perturbation, is also considered.

  • 436. Heikkola, E.
    et al.
    Miettinen, Kaisa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Nieminen, P.
    Applying IND-NIMBUS to a Design Problem in High-Power Ultrasonics2005Report (Other academic)
  • 437.
    Bortolin, Gianantonio
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Gutman, P. O.
    Nilsson, B.
    Curl estimation in multi-ply paperboard2005In: Pract. Papermaking Conf., 2005, p. 733-754Conference paper (Refereed)
    Abstract [en]

    This paper describes a grey box model for the curl and twist of the carton board produced at AssiDomän Frövi, Sweden. The main equations are based on classical lamination theory of composite materials, and each constituent ply is considered as a macroscopic homogeneous, elastic medium. The model used data from June to September 2004, and shows a general agreement between predicted and measured curvatures. Regularization and backwards elimination were used to cope with the low identifiability of the problem. The model was then complemented with a sub-model of immeasurable/unmodelled disturbances estimated with an extended Kalman filter.

  • 438. Rehbinder, H.
    et al.
    Hu, Xiaoming
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Drift-free attitude estimation using quasi-linear observers2005In: NEW DIRECTIONS AND APPLICATIONS IN CONTROL THEORY / [ed] Dayawansa, WP; Lindquist, A; Zhou, Y, 2005, Vol. 321, p. 321-336Conference paper (Refereed)
    Abstract [en]

    In this paper we study the attitude estimation problem for an accelerated rigid body using gyros and accelerometers. The application in mind is that of a walking robot and particular attention is paid to the large and abrupt changes in accelerations that can be expected in such an environment. We propose a state estimation algorithm that fuses data from rate gyros and accelerometers to give long-term drift free attitude estimates. The algorithm does not use any local parameterization of the rigid body kinematics and can thus be used for a rigid body performing any kind of rotations. The algorithm is a combination of two non-standard, but in a sense linear, Kalman filters between which a trigger based switching takes place. The kinematics representation used makes it possible to construct a linear algorithm that can be shown to give convergent estimates for this nonlinear problem. The state estimator is evaluated in simulations demonstrating how the estimates are long term stable even in the presence of gyrodrift.

  • 439.
    Gustavi, Tove
    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.
    Formation control for mobile robots with limited sensor information2005In: 2005 IEEE International Conference on Robotics and Automation (ICRA), Vols 1-4, 2005, p. 1791-1796Conference paper (Refereed)
    Abstract [en]

    In this paper mobile multi-agent systems with limited sensor information are studied. Some control algorithms are proposed that do not require global information, and are easy to implement. First two basic controls for a single mobile agent tracking another moving object are derived. Then it is shown how these basic controls can be combined in order to achieve more complex formations.

  • 440.
    Klamroth, Kathrin
    et al.
    Institute of Applied Mathematics, University of Erlangen Nuremberg.
    Miettinen, Kaisa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Interactive Approach Utilizing Approximations of the Nondominated Set2005Report (Other academic)
    Abstract [en]

        We present a new interactive approach for solving multicriteria opti-mization problems. We produce rough approximations of the nondomi-nated set and let the decision maker indicate with the help of referencepoints where to refine the approximation. In this way, (s)he iterativelydirects the search towards the best nondominated solution. After the deci-sion maker has identified the most interesting region of the nondominatedset, the final solution can be fine-tuned with existing interactive methods.We suggest different ways of updating the reference point as well as dis-cuss visualizations that can be used in comparing different nondominatedsolutions. The new method is computationally inexpensive and easy to usefor the decision maker.

  • 441. Ojalehto, V.
    et al.
    Miettinen, Kaisa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Mäkelä, Marko M.
    Department of Mathematical Information Technology, University of Jyväskylä.
    Issues of Implementing IND-NIMBUS Software for Interactive Multiobjective Optimization2005Report (Other academic)
  • 442.
    Jönsson, Ulf
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Megretski, A.
    Limit cycle analysis using a system right inverse2005In: 2005 44th IEEE Conference on Decision and Control & European Control Conference, Vols 1-8, 2005, p. 2951-2956Conference paper (Refereed)
    Abstract [en]

    The variational system obtained by linearizing a dynamical system along a limit cycle is always non-invertible. This follows because the limit cycle is only unique modulo time translation. It is shown that questions such as uniqueness, robustness, and computation of limit cycles can be addressed using a right inverse of the variational system. Small gain arguments are used in the analysis.

  • 443.
    Jönsson, Ulf T.
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Megretski, A.
    Local robustness of hyperbolic limit cycles2005In: NEW DIRECTIONS AND APPLICATIONS IN CONTROL THEORY, 2005, p. 165-180Conference paper (Refereed)
    Abstract [en]

    Local robustness of limit cycles are investigated for systems that can be modeled as a feedback interconnection of an exponentially stable linear system with a nonlinear function. Conditions are given under which the limit cycle and the number of unstable modes persist for sufficiently small dynamic perturbations.

  • 444. Fujioka, H.
    et al.
    Kao, C. -Y
    Almér, Stefan
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Jönsson, Ulf
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    LQ optimal control synthesis for a class of pulse modulated systems2005Conference paper (Refereed)
    Abstract [en]

    We consider linear quadratic optimal control for a class of pulse-width-modulated systems. The problem is motivated from a practical application - digital control of switching power converters. The control synthesis problem is posed based on a sampled data model of the original switching dynamics and a linear quadratic criterion that takes the inter sampling behavior into account.

  • 445.
    Bortolin, Gianantonio
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Modelling and grey-box identification of curl and twist in paperboard manufacturing2005Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    The contents of this thesis can be divided into two main parts. The first one is the development of an identification methodology for the modelling of complex industrial processes. The second one is the application of this methodology to the curl and twist problem.

    The main purpose behind the proposed methodology is to provide a schematic planning, together with some suggested tools, when confronted with the challenge of building a complex model of an industrial process. Particular attention has been placed to outlier detection and data analysis when building a model from old, or historical, process data.

    Another aspect carefully handled in the proposed methodology is the identifiability analysis. In fact, it is rather common in process modelling that the model structure turns out to be weakly identifiable. Consequently, the problem of variable selection is treated at length in this thesis, and a new algorithm for variable selection based on regularization has been proposed and compared with some of the classical methods, yielding promising results.

    The second part of the thesis is about the development of a curl predictor. Curl is the tendency of paper of assuming a curved shape and is observed mainly during humidity changes. Curl in paper and in paperboard is a long-standing problem because it may seriously affect the processing of the paper. Unfortunately, curl cannot be measured online, but only in the laboratory after that an entire tambour has been produced. The main goal of this project is then to develop a model for curl and twist, and eventually to implement it as an on-line predictor to be used by the operators and process engineers as a tool for decision/control.

    The approach we used to tackle this problem is based on grey-box modelling. The reasons for such an approach is that the physical process is very complex and nonlinear. The influence of some inputs is not entirely understood, and besides it depends on a number of unknown parameters and unmodelled/unmesurable disturbances.

    Simulations on real data show a good agreement with the measurement, particularly for MD and CD curl, and hence we believe that the model has an usable accuracy for being implemented as an on-line predictor.

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    FULLTEXT01
  • 446.
    Gustavi, Tove
    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.
    Karasalo, Maja
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Multi-robot formation control and terrain servoing with limited sensor information2005In: IFAC Proc. Vol. (IFAC-PapersOnline), 2005, p. 577-582Conference paper (Refereed)
    Abstract [en]

    in this paper mobile multi-agent systems with limited sensor information are studied. Two control algorithms are proposed that do not require global information, and are easy to implement. The control problems are motivated by robotic applications such as cleaning, grass mowing and land mines detection, where a common control problem is the complete coverage path planning, for which it is known that parallel formation is optimal. The proposed control algorithms provide terrain servoing for the leading robot and parallel formation keeping for the followers, both of which are only based on measurements from range sensors.

  • 447.
    Karasalo, Maja
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Johansson, Linda-Maria
    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.
    Johansson, Karl Henrik
    KTH, School of Electrical Engineering (EES), Automatic Control.
    Multi-robot terrain servoing with proximity sensors2005In: 2005 IEEE International Conference on Robotics and Automation (ICRA), 2005, p. 2791-2796Conference paper (Refereed)
    Abstract [en]

    The problem of coordinating a team of robots with heterogeneous sensing capabilities is studied in this paper. A control structure is proposed that combines terrain servoing for the leading robot with on-line formation planning and path following for the followers, while enabling obstacle avoidance for all the robots.

  • 448.
    Gustavi, Tove
    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.
    Navigation coordination for multi-agent systems with limited sensor information2005In: 2005 International Conference on Control and Automation (ICCA), Vols 1 and 2, 2005, p. 77-82Conference paper (Refereed)
    Abstract [en]

    In this paper mobile multi-agent systems with limited sensor information are studied. Some control algorithms are proposed that do not require global information, and are easy to implement. First two basic controls for serial and parallel formations are derived. Then it is demonstrated how these basic controls can be combined in order to achieve more complex formations. Combined with an obstacle avoidance controller, the emerging system can perform quite complex navigation tasks.

  • 449.
    Lindquist, Anders
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory. KTH, School of Engineering Sciences (SCI), Centres, Center for Industrial and Applied Mathematics, CIAM. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    New Directions and Applications in Control Theory2005Collection (editor) (Refereed)
  • 450.
    Blomqvist, Anders
    et al.
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Wahlberg, Bo
    KTH, School of Electrical Engineering (EES), Automatic Control.
    On frequency weighting in autoregressive spectral estimation2005In: IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings, 2005, p. 245-248Conference paper (Refereed)
    Abstract [en]

    This paper treats the problem of approximating a complex stochastic process in a given frequency region by an estimated autoregressive (AR) model. Two frequency domain approaches are discussed: a weighted frequency domain maximum likelihood method and a prefiltered covariance extension method based on the theory of Lindquist and co-workers. It is shown that these two approaches are very closely related and can both be formulated as convex optimization problems. An examples illustrating the methods and the effect of prefiltering/weighting is provided. The results show that these methods are capable of tuning the AR model fit to a specified frequency region.

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