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ф Travel Report
Visit to
Center of Excellence MTA SZTAKI
Computer and Automation Institute of the
Hungarian Academy of Sciences
2001-08-20 --- 09-30
Hхkan Hjalmarsson
Dept. of Signals, Sensors and Systems
Royal Institute of Technology
S-100 44 Stockholm, Sweden
HYPERLINK "mailto:hakan.hjalmarsson@s3.kth.se"hakan.hjalmarsson@s3.kth.se
Introduction
This is a brief report of my visit to the Computer and Automation Institute of the Hungarian Academy of Sciences (MTA SZTAKI) during the period 2001-08-20 --- 09-30. The initiative of this visit was taken by my host Dr Laszlo Gerencser, Head of the Stochastic Systems Group.
The visit was sponsored by MTA SZTAKI as part of their EU Center of Excellence activities. This support is gratefully acknowledged.
Interaction at the Institute
During my visit I had the opportunity to present two seminars at the institute. In one seminar I presented my home department and in particular our activities in Micro Electro Mechanical Systems (MEMS) which has bearings on the activities in the Analogical and Neural Computing Laboratory at the institute. In the other seminar I focused more on the activities in my own group, and in particular my own work on controller tuning.
I also had some interesting discussions with Professor Josef Bokor which revealed that we have common research interests in the area of identification of nonlinear systems which deserves further exploration.
Most of my time was spent with Dr Laszlo Gerencser, Head of the Stochastic Systems Group. For a number of years I have been working on a controller tuning method known as Iterative Feedback Tuning (IFT). In parallell, Professor Gerencser has been contributing to the development of a stochastic approximation method known as Simultaneous Perturbation Stochastic Approximation (SPSA), Recently he and his co-workers have shown that the randomization method on which SPSA is based has some very interesting convergence properties when applied to noise free problems. One purpose of my visit was to explore if these ideas also could be adapted to IFT and what randomization in general has to offer for control problems. This visit also gave us the opportunity to explore what other research interests we have in common. A significant part of my visit was spent on discussions with Professor Gerencser on possible future joint projects.
Scientific work
Although much of my time was devoted to discussions with Professor Gerencser on possible future research projects, we early on decided that it was important that the visit also resulted in some hard results. During the visit, we did joint work in three different areas:
Randomization in Iterative Feedback Tuning.
As mentioned earlier, one purpose of my visit was to explore if randomization algorithms can be combined with IFT. This work resulted in the paper ``Randomized Iterative Feedback Tuning'', L. Gerencser, Z. Vago and H. Hjalmarsson which has been submitted to the 2002 IFAC World Congress.
Experiment Design.
Since a couple of years I have been active in experiment design for system identification by way of a PhD project. We have been able to develop an experiment design procedure which can be stated as a convex optimization problem. However, the problem remained that the cost function depends on the unknown system. During my visit at SZTAKI this obstacle was passed and a procedure was developed where the system is recursively identified and the experiment design successively adapted. The method is asymptotically optimal, i.e. it performs as well as if the true system was known. A manuscript to be submitted to Automatica is in preparation.
Iterative Learning Control (ILC).
ILC is a method which can be used to generate a suitable feedforward control for systems where the same trajectory is taken over and over again. This input is generated by a series of experiments where the feedforward input is successively improved. Convergence and optimality of these iterations has previously been proved for noise free systems. During my visit we developed a Stochastic Approximation version of the algorithm which converges also under noisy conditions. A manuscript to be submitted to Automatica is in preparation.
Future collaboration
The competencies of the Stochastic Systems Group at SZTAKI and the Automatic Control Group at KTH are to a large extent complementary. This lead to the contributions in the areas mentioned above, i.e. randomization in Iterative Feedback Tuning, experiment design and iterative learning control. It is thus very natural to continue and extend the collaboration on these subjects and other topics involving control and stochastics. There also seems to be a potential for a joint collaboration between the Stochastic Systems Group, the Systems and Control Laboratory and the Automatic Control Group at KTH in the area of non-linear (stochastic) systems.
Possible frameworks for this is the ERCIM (The European Research Consortium for Informatics and Mathematics) Working Group of Control and Systems where SZTAKI is participating and ERNSI (the European Research Network on System Identification) where KTH is participating.
An interesting idea would be joint supervision of PhD students. However, presently there seems to be some practical problems, especially related to the funding system at KTH.
Concluding remarks
I would like to conclude this report with some personal remarks. I found the visit at SZTAKI very fruitful and most enjoyable and a number of people contributed to this. The resources and support at the institute were exemplary and in particular I am very grateful to Mr Geza Haidegger for all help regarding administrative matters.
Finally, very special thanks to Laszlo and Zsusanna for your hospitality and the enormous time you spent with me on research problems and all extracurricular activities that you arranged (not to mention your effort spent on translating an uncountable number of Hungarian menus for me).
Thanks guys!
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