| 1. |
- 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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| 2. |
- 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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| 3. |
- Henrion, Didier, et al.
(författare)
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Reduced LMIs for Fixed-Order Polynomial Controller Design
- 2004
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Ingår i: Proceedings of the 16th International Symposium on Mathematical Theory of Networks and Systems. - 9056825178
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Konferensbidrag (refereegranskat)abstract
- A reduction procedure based on semidefinite programming duality is applied to LMI conditions for fixed-order scalar linear controller design in the polynomial framework. It is namely shown that the number of variables in the reduced design LMI is equal to the difference between the open-loop plant order and the desired controller order. A standard linear system of equations must then be solved to retrieve the controller parameters. Therefore high computational load is not necessarily expected when the number of controller parameters is large, but rather when a large number of plant parameters are to be controlled with a small number of controller paramters. Tailored interior-point algorithms dealing with the specific structure of the reduced design LMI are also discussed.
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| 4. |
- Ståhl Gunnarsson, Karin, et al.
(författare)
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Clearance of Flight Control Laws using Linear Fractional Transformations
- 2004
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Ingår i: Proceedings of the 2004 AIAA Guidance, Navigation and Control Conference and Exhibit. - Reston, Virigina : American Institute of Aeronautics and Astronautics. - 9781624100734
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Konferensbidrag (refereegranskat)abstract
- The problem of flight clearance of linear stability requirements in the complete flight evelope is studied. The approach is to use mu-analysis of linear fractional transformations description of the system dynamics augmented with an uncertainty model of the clearance criteria. Two methods to derive the linear fractional transformations are used and compared: the Trends and Bands method and rational approximations. The two approaches are applied to a UAV demostrator model. The resulting models are analyzed by mu-sensitivites in order to demonstrate how this can be used to reduce the order of the linear fractional transformations description. A number of algorithms to compute upper and lower bounds on mu are also compared. Results from applying the clearance criteria to the UAV demonstrator model are given.
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| 5. |
- Vandenberghe, Lieven, et al.
(författare)
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Interior-Point Algorithms for Semidefinite Programming Problems Derived from the KYP Lemma
- 2005
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Ingår i: Positive Polynomials in Control. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 3540239480 ; , s. 195-238
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Bokkapitel (refereegranskat)abstract
- We discuss fast implementations of primal-dual interior-point methods for semidefinite programs derived from the Kalman-Yakubovich-Popov lemma, a class of problems that are widely encountered in control and signal processing applications. By exploiting problem structure we achieve a reduction of the complexity by several orders of magnitude compared to general-purpose semidefinite programming solvers.
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| 6. |
- Wallin, Ragnar, 1962-, et al.
(författare)
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A Cutting Plane Method for Solving KYP-SDPs
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Semidefinite programs originating from the Kalman-Yakubovich-Popov lemma are convex optimization problems and there exist polynomial time algorithms that solve them. However, the number of variables is often very large making the computational time extremely long. Algorithms more efficient than general purpose solvers are thus needed. To this end structure exploiting algorithms have been proposed, based on the dual formulation. In this paper a cutting plane algorithm is proposed. In a comparison with a general purpose solver and a structure exploiting solver it is shown that the cutting plane based solver can handle optimization problems of much higher dimension.
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| 7. |
- Wallin, Ragnar, 1962-, et al.
(författare)
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A Cutting Plane Method for Solving KYP-SDPs
- 2008
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Ingår i: Automatica. - : Elsevier. - 0005-1098 .- 1873-2836. ; 44:2, s. 418-429
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Tidskriftsartikel (refereegranskat)abstract
- Semidefinite programs originating from the Kalman-Yakubovich-Popov lemma are convex optimization problems and there exist polynomial time algorithms that solve them. However, the number of variables is often very large making the computational time extremely long. Algorithms more efficient than general purpose solvers are thus needed. To this end structure exploiting algorithms have been proposed, based on the dual formulation. In this paper a cutting plane algorithm is proposed. In a comparison with a general purpose solver and a structure exploiting solver it is shown that the cutting plane based solver can handle optimization problems of much higher dimension.
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| 8. |
- Wallin, Ragnar, 1962-, et al.
(författare)
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A Decomposition Approach for Solving KYP-SDPs
- 2005
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Ingår i: Proceedings of the 16th IFAC World Congress. - 9783902661753 ; , s. 1021-1021
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Konferensbidrag (refereegranskat)abstract
- Semidefinite programs originating from the Kalman-Yakubovich-Popov lemma are convex optimization problems and there exist polynomial time algorithms that solve them. However, the number of variables is often very large making the computational time extremely long. Algorithms more efficient than general purpose solvers are thus needed. In this paper a generalized Benders decomposition algorithm is applied to the problem to improve efficiency.
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| 9. |
- Wallin, Ragnar, 1962-, et al.
(författare)
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KYPD : A Solver for Semidefinite Programs Derived from the Kalman-Yakubovich-Popov Lemma
- 2004
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Ingår i: Proceedings of the 2004 IEEE International Symposium on Computer Aided Control System Design. - Linköping : Linköping University Electronic Press. - 0780386361 ; , s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Semidenite programs derived from the Kalman-Yakubovich-Popov lemma are quite common in control and signal processing applications. The programs are often of high dimension making them hard or impossible to solve with general-purpose solvers. KYPD is a customized solver for KYP-SDPs that utilizes the inherent structure of the optimization problem thus improving efficiency signicantly.
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| 10. |
- Wallin, Ragnar, 1962-, et al.
(författare)
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User's Guide to Kypd_Solver
- 2006
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This package contains software for solving semidefinite programs (SDPs) originating from the Kalman-Yakubovich-Popov lemma. A presentation of the software is given and the options included are presented and described.
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