| 1. |
- Agüero, Juan C., et al.
(författare)
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Accuracy of linear multiple-input multiple-output (MIMO) models obtained by maximum likelihood estimation
- 2012
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 48:4, s. 632-637
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study the accuracy of linear multiple-input multiple-output (MIMO) models obtained by maximum likelihood estimation. We present a frequency-domain representation for the information matrix for general linear MIMO models. We show that the variance of estimated parametric models for linear MIMO systems satisfies a fundamental integral trade-off. This trade-off is expressed as a multivariable 'water-bed' effect. An extension to spectral estimation is also discussed.
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| 2. |
- Alberer, Daniel, et al.
(författare)
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System Identification for Automotive Systems : Opportunities and Challenges
- 2012
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Ingår i: Identification for automotive systems. - London : Springer Nature. ; , s. 1-
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Konferensbidrag (refereegranskat)abstract
- Without control many essential targets of the automotive industry could not be achieved. As control relies directly or indirectly on models and model quality directly influences the control performance, especially in feed-forward structures as widely used in the automotive world, good models are needed. Good first principle models would be the first choice, and their determination is frequently difficult or even impossible. Against this background methods and tools developed by the system identification community could be used to obtain fast and reliably models, but a large gap seems to exist: neither these methods are sufficiently well known in the automotive community, nor enough attention is paid by the system identification community to the needs of the automotive industry. This introduction summarizes the state of the art and highlights possible critical issues for a future cooperation as they arose from an ACCM Workshop on Identification for Automotive Systems recently held in Linz, Austria.
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| 3. |
- Bombois, Xavier, et al.
(författare)
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Identification for robust H-2 deconvolution filtering
- 2010
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 46:3, s. 577-584
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Tidskriftsartikel (refereegranskat)abstract
- This paper addresses robust deconvolution filtering when the system and noise dynamics are obtained by parametric system identification. Consistent with standard identification methods, the uncertainty in the estimated parameters is represented by an ellipsoidal uncertainty region. Three problems are considered: (1) computation of the worst case H-2 performance of a given deconvolution filter in this uncertainty set; (2) design of a filter which minimizes the worst case H-2 performance in this uncertainty set; (3) input design for the identification experiment, subject to a limited input power budget, such that the filter in (2) gives the smallest possible worst case H-2 performance. It is shown that there are convex relaxations of the optimization problems corresponding to (1) and (2) while the third problem can be treated via iterating between two convex optimization problems.
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| 4. |
- Bombois, Xavier, et al.
(författare)
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Optimal experiment design for hypothesis testing applied to functional magnetic resonance imaging
- 2011
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Ingår i: Proceedings of the 18th IFAC World Congress. ; , s. 9953-9958
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Konferensbidrag (refereegranskat)abstract
- Hypothesis testing is a classical methodology of making decisions using experimental data. In hypothesis testing one seeks to discover evidence that either accepts or rejects a given null hypothesis H0. The alternative hypothesis H1 is the hypothesis that is accepted when H0 is rejected. In hypothesis testing, the probability of deciding H1 when in fact H0 is true is known as the false alarm rate, whereas the probability of deciding H1when in fact H1is true is known as the detection rate (or power) of the test. It is not possible to optimize both rates simultaneously. In this paper, we consider the problem of determining the data to be used for hypothesis testing that maximize the detection rate for a given false alarm rate. We consider in particular a hypothesis test which is relevant in functional magnetic resonance imaging (fMRI).
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| 5. |
- Briat, Corentin, et al.
(författare)
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An axiomatic fluid-flow model for congestion control analysis
- 2011
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Ingår i: 2011 50th IEEE Conference on Decision and Control andEuropean Control Conference (CDC-ECC). ; , s. 3122-3129
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Konferensbidrag (refereegranskat)abstract
- An axiomatic model for congestion control isderived. The proposed four axioms serve as a basis for theconstruction of models for the network elements. It is shownthat, under some assumptions, some models of the literature canbe recovered. A single-buffer/multiple-users topology is finallyderived and studied for illustration.
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| 6. |
- Briat, Corentin, et al.
(författare)
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Nonlinear state-dependent delay modeling and stability analysis of internet congestion control
- 2010
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Ingår i: 49TH IEEE CONFERENCE ON DECISION AND CONTROL (CDC). - 9781424477463 ; , s. 1484-1491
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Konferensbidrag (refereegranskat)abstract
- It is shown that the queuing delay involved in the congestion control algorithm is state-dependent and does not depend on the current time. Then, using an accurate formulation for buffers, networks with arbitrary topologies can be built. At equilibrium, our model reduces to the widely used setup by Paganini et al. Using this model, the delay-derivative is analyzed and it is proved that the delay time-derivative does not exceed one for the considered topologies. It is then shown that the considered congestion control algorithm globally stabilizes a delay-free single buffer network. Finally, using a specific linearization result for systems with state-dependent delays from Cooke and Huang, we show the local stability of the single bottleneck network.
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| 7. |
- Chotteau, Véronique, et al.
(författare)
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Tuning of dissolved oxygen and pH PID control parameters in large scale bioreactor by lag control
- 2012
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Ingår i: Proceedings of the 21st Annual Meeting of the European Society for Animal Cell Technology (ESACT). - Dordrecht : Springer Netherlands. - 9789400708839 ; , s. 327-330
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Konferensbidrag (refereegranskat)abstract
- A method has been developed to tune the DO and pH controller PID parameters for pilot / large scale mammalian cultivation. Our approach is to identify a model of the variable to be controlled (e.g. DO, pH) and to design several possible PID controllers based on this model. The controllers were first tested in computer simulations, followed by wet simulation and finally the best controller was tested on the real process. The approach is developed for the tuning of the DO controller of a 50 L bioreactor using microbubble continuous oxygen flow. The method, called lag control here, is based on a lead lag control design using Bode analysis where the prediction part is omitted. Experiments show that the approach results in a highly satisfactory DO control. The oxygen microbubbles were almost completely consumed before reaching the liquid surface so the oxygen flow used to maintain the DO gave an excellent indication of the cellular oxygen consumption. The control system was robust against all the perturbations, i.e. cell growth, cell bleed, addition of air-saturated fresh medium, DO set point change and a second gas sparger used to strip out the carbon dioxide. This approach was also successfully used for the tuning of a 400 L bioreactor DO controller and pH controller.
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| 8. |
- Eckhard, Diego, et al.
(författare)
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Input design as a tool to improve the convergence of PEM
- 2013
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 49:11, s. 3282-3291
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Tidskriftsartikel (refereegranskat)abstract
- The Prediction Error Method (PEM) is related to an optimization problem built on input/output data collected from the system to be identified. It is often hard to find the global solution of this optimization problem because the corresponding objective function presents local minima and/or the search space is constrained to a nonconvex set. The shape of the cost function, and hence the difficulty in solving the optimization problem, depends directly on the experimental conditions, more specifically on the spectrum of the input/output data collected from the system. Therefore, it seems plausible to improve the convergence to the global minimum by properly choosing the spectrum of the input; in this paper, we address this problem. We present a condition for convergence to the global minimum of the cost function and propose its inclusion in the input design. We present the application of the proposed approach to case studies where the algorithms tend to get trapped in nonglobal minima.
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| 9. |
- Eckhard, Diego, et al.
(författare)
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Mean-squared error experiment design for linear regression models
- 2012
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Ingår i: 16th IFAC Symposium on System Identification. - : IFAC. - 9783902823069 ; , s. 1629-1634
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Konferensbidrag (refereegranskat)abstract
- This work solves an experiment design problem for a linear regression problem using a reduced order model. The quality of the model is assessed using a mean square error measure that depends linearly on the parameters. The designed input signal ensures a predefined quality of the model while minimizing the input energy.
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| 10. |
- Eckhard, Diego, et al.
(författare)
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On the convergence of the Prediction Error Method to its global minimum
- 2012
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Ingår i: 16th IFAC Symposium on System Identification. - : IFAC. - 9783902823069 ; , s. 698-703
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Konferensbidrag (refereegranskat)abstract
- The Prediction Error Method (PEM) is related to an optimization problem built on input/output data collected from the system to be identified. It is often hard to find the global solution of this optimization problem because the corresponding objective function presents local minima and/or the search space is constrained to a nonconvex set. The existence of local minima, and hence the difficulty in solving the optimization, depends mainly on the experimental conditions, more specifically on the spectrum of the input/output data collected from the system. It is therefore possible to avoid the existence of local minima by properly choosing the spectrum of the input; in this paper we show how to perform this choice. We present sufficient conditions for the convergence of PEM to the global minimum and from these conditions we derive two approaches to avoid the existence of nonglobal minima. We present the application of one of these two approaches to a case study where standard identification toolboxes tend to get trapped in nonglobal minima.
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