(Saint Petersburg, September, 1999)

6-th Saint Petersburg Symposium on Adaptive Systems Theory took place at St. Petersburg on September 7 - 9, 1999. The Symposium was organized by Russian National Committee on Automatic Control, by St. Petersburg Informatics and Control Society, by St. Petersburg State University, by Institute for Problems of Mechanical Engineering of Russian Academy of Sciences, by St. Petersburg Institute for Informatics and Automation of Russian Academy of Sciences. The Symposium was sponsored by Russian Foundation for Basic Research.

6-th Saint Petersburg Symposium on Adaptive Systems Theory was dedicated to the memory of outstanding Scientist Ya.Z. Tsypkin who has made an invaluable contribution into the control theory and into adaptive systems theory particularly.

6-th Saint Petersburg Symposium on Adaptive Systems Theory (SPAS'99) was an appreciable event not only for Russian Science, but also for World Science. Many well known Scientists took places at the Symposium and presented their papers. Among well known surnames we see I.D. Landau (France), L.Ljung (Sweden), A. Lindquist (Sweden), D.D. Siljak (USA), K. Furuta (Japan) and many others. Among russian speakers we see B.T. Polyak, V.Yu. Rutkovsky, V.N. Fomin, R.M. Yusupov, A.L. Fradkov, A.V. Timofeev and many others.

The Symposium's program included items of adaptive control theory applications with the accent on the time border for passage to the 21-t century: what is well made till now? What are the most actual scientific problems for 21-t century? So from this point of view it is evident the Symposium's subjects: Mathematical theory of adaptive and intelligent systems; Estimation, identification and filtering; Sensitivity and invariance of control systems; Intelligent and adaptive control; Computer-aided design of adaptive systems; Applications of adaptive control, including industrial, aerospace, marine, economics, finance, etc. Nevertheless one item of the Symposium's program could be separated as the central one and it was prevalent and penetrating all the other questions. This item is the adaptive control by nonlinear systems, nonlinear dynamics and adaptive control by complex systems.

There were a lot of other speakers and topics. The conclusion is single: the World Science and Russian Scientific Society have lost in the face of Ya.Z. Tsipkin the outstanding Scientist and the beautiful Man.

The Proceedings of the Symposium consist of two volumes. The first contains the papers written in English. The second one contains the papers written in Russian.