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| 2. |
- Garulli, Andrea, et al.
(författare)
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Robust Finite-Frequency H2 Analysis of Uncertain Systems
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In many applications, design or analysis is performed over a finite frequency range of interest. The importance of the H2/robust H2 norm highlights the necessity of computing this norm accordingly. This paper provides different methods for computing upper bounds on the robust finite-frequency H2 norm for systems with structured uncertainties. An application of the robust finite-frequency H2 norm for a comfort analysis problem of an aero-elastic model of an aircraft is also presented.
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| 3. |
- Garulli, Andrea, et al.
(författare)
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Robust finite-frequency H2 analysis of uncertain systems with application to flight comfort analysis
- 2013
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Ingår i: Control Engineering Practice. - : Elsevier. - 0967-0661 .- 1873-6939. ; 21:6, s. 887-897
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Tidskriftsartikel (refereegranskat)abstract
- In many applications, design or analysis is performed over a finite-frequency range of interest. The importance of the H2 norm highlights the necessity of computing this norm accordingly. This paper provides different methods for computing upper bounds of the robust finite-frequency H2 norm for systems with structured uncertainties. An application of the robust finite-frequency H2 norm for a comfort analysis problem of an aero-elastic model of an aircraft is also presented.
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| 4. |
- Gutiérrez Pérez, Cristina, 1972, et al.
(författare)
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High frequency of cognitive dysfunction before stroke in the elderly
- 2011
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Ingår i: International Journal of Geriatric Psychiatry. - : Wiley. - 1099-1166 .- 0885-6230. ; 26:6, s. 622-629
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Tidskriftsartikel (refereegranskat)abstract
- Objectives We examined cognitive functions before and in acute phase of stroke studying frequency and profile of cognitive impairment and relationships between cognitive status.MethodsSeventy-four patients with early phase after stroke and 49 healthy controls were included and examined using the Mini-Mental State Examination (MMSE) and a battery of neuropsychological tests. Cognitive status before stroke-onset was investigated using Cognitive Impairment Questionnaire.ResultsCognitive impairments were present in 96% of patients after stroke onset using the battery of neuropsychological tests and in 39% of patients using the MMSE, but in only 9% of controls. Seventy-six percent exhibited reduced executive function and 75% reduced psychomotor tempo. Cognitive dysfunction was present in 52% before stroke onset without any impact on the frequency of impairment in the various cognitive areas in early phase after stroke.ConclusionsCognitive impairment is frequent before the onset of stroke among older people and may partially explain the very high frequency of cognitive impairment observed after stroke onset.
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| 5. |
- Hansson, Anders, et al.
(författare)
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Comparison of Two Structure-Exploiting Optimization Algorithms for Integral Quadratic Constraints
- 2003
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Ingår i: Proceedings of the 4th IFAC symposium on Robust Control Design. - Linköping : Linköping University Electronic Press. - 9780080440125
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Konferensbidrag (refereegranskat)abstract
- As the semidefinite programs that result from integral quadratic contstraints are usually large it is important to implement efficient algorithms. The interior-point algorithms in this paper are primal-dual potential reduction methods and handle multiple constraints. Two approaches are made. For the first approach the computational cost is dominated by a least-squares problem that has to be solved in each iteration. The least squares problem is solved using an iterative method, namely the conjugate gradient method. The computational effort for the second approach is dominated by forming a linear system of equations. This systems of equations is used to compute the search direction in each iteration. If the number of variables are reduced by solving a smaller subproblem the resulting system has a very nice structure and can be solved efficiently. The first approach is more efficient for larger problems but is not as numerically stable.
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| 6. |
- Hansson, Anders, et al.
(författare)
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Efficient Implementations of Interior-Point Methods for Integral Quadratic Constraints
- 2001
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Ingår i: Proceedings of the Fourth SIAM Conference on Linear Algebra in Signals, Systems and Control.
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Konferensbidrag (refereegranskat)abstract
- We describe two strategies for exploiting structure in implementations of interior-point methods for the semidefinite programs (SDPs) that result from integral quadratic constraints. The first approach uses inexact search directions computed by the conjugate gradient algorithm. In the second approach we solve the problem via the dual. Simplifying the dual problem results in an SDP that has fewer variables (O(n)) than the primal SDP (O(n2) variables), and that can be solved efficiently using standard methods.
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| 7. |
- Hansson, Anders, et al.
(författare)
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Maximum Likelihood Estimation of Gaussian Models with Missing Data : Eight Equivalent Formulations
- 2011
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this paper we derive the maximum likelihood problem for missing data from a Gaussian model. We present in total eight different equivalent formulations of the resulting optimization problem, four out of which are nonlinear least squares formulations. Among these formulations are also formulations based on the expectation-maximization algorithm. Expressions for the derivatives needed in order to solve the optimization problems are presented. We also present numerical comparisons for two of the formulations for an ARMAX model.
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| 8. |
- Hansson, Anders, et al.
(författare)
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Maximum Likelihood Estimation of Gaussian Models with Missing Data : Eight Equivalent Formulations
- 2012
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Ingår i: Automatica. - : Elsevier. - 0005-1098 .- 1873-2836. ; 48:9, s. 1955-1962
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we derive the maximum likelihood problem for missing data from a Gaussian model. We present in total eight different equivalent formulations of the resulting optimization problem, four out of which are nonlinear least squares formulations. Among these formulations are also formulations based on the expectation-maximization algorithm. Expressions for the derivatives needed in order to solve the optimization problems are presented. We also present numerical comparisons for two of the formulations for an ARMAX model.
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| 9. |
- Hansson, Jörgen, et al.
(författare)
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Clearance of Flight Control Laws for Time-Varying Parameters
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this article exponential stability of the closed loop for the Saab AB VEGAS model controlled by a gain-scheduled linear fractional transformation controller is investigated for time-varying Mach-number. The analysis is based on parameter-dependent Lyapunov-functions which are obtained by investigating feasibility of linear matrix inequalities.
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| 10. |
- Harju, Janne, 1980-, et al.
(författare)
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Utilizing Low Rank Properties when Solving KYP-SDPs
- 2006
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Ingår i: Proceedings of the 45th IEEE Conference on Decision and Control. - Linköping : Linköping University Electronic Press. - 1424401712 ; , s. 5150-5155
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Konferensbidrag (refereegranskat)abstract
- Semidefinite programs and especially those derived from the Kalman-Yakubovich-Popov lemma are quite common in control applications. KYPD is a dedicated solver for KYP-SDPs. It solves the optimization problem via the dual SDP. The solver is iterative. In each step a Hessian is formed and a linear system of equations is solved. The calculations can be performed much faster if we utilize sparsity and low rank structure. We show how to transform a dense optimization problem into a sparse one with low rank structure. A customized calculation of the Hessian is presented and investigated.
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