Suddenly and unexpectedly, the Russian Academy of Sciences and the Institute of Control Sciences in Moscow, with deep sorrows, announced that Academician Yakov Zalmanovich Tsypkin passed away on December 2, 1997.

Yakov Zalmanovich Tsypkin was an outstanding scientist, professor, and a member of the Russian Academy of Sciences. He was a part of the control engineering community of the International Federation on Automatic Control (IFAC) for many years. He served IFAC in many different functions. He was the Chairman of the IFAC Technical Committee on Theory between 1978 and 1981 and served as the Vice-Chairman of the Publication Committee in the current triennium. In 1994 he became the Chairman of the Russian National Committee of Automatic Control, the Russian NMO of IFAC.

Yakov Z. Tsypkin was born in the city Dnepropetrovsk (former USSR, now Ukraine) on September 19, 1919. All his creative life was connected with the Institute of Automatic and Remote Control (at present, the Institute of Control Sciences of the Russian Academy of Sciences), where he joined in the forties as a participant of A.A. Andronov's Seminar. In 1950, he became a senior scientific researcher of the Institute, and since 1956 he has been the chief of a laboratory.

Ya. Z. Tsypkin made significant contributions in many fields of the modern control theory. In the forties and fifties he set up the foundation of the theory of relay, sample-data and discrete-time control systems. His books on these subjects have become classical. Such notions as "Tsypkin criterion", "Tsypkin rule", "Tsypkin locus" enriched the golden fund of the regulation theory.

In the sixties, Yakov Z. Tsypkin suggested a new approach to the theory of adaptive and learning systems based on the stochastic approximation ideas. It resulted in the creation of optimal and robust algorithms of estimation, identification, and optimization. Lately, his interest was focused on the theory of robust control, where he obtained general criteria of robust stability and new methods of disturbance attenuation. Yakov Z. Tsypkin is the founder of an authoritative scientific school. Among his students there are dozens of candidates and doctors of science. Many of them have become prominent researchers and are leaders of their own scientific trends.

Yakov Zalmanovich Tsypkin is a laureate of the Lenin Prize, the greatest recognition for scientific achievements in the former Soviet Union, and the Andonov Prize of the Russian Academy of Sciences. He was awarded by decorations and medals by the Government for his scientific activity and achievements. Professor Ya.Z. Tsypkin was the veteran of the Second World War.

Academician Ya.Z. Tsypkin was the teacher and friend of many Yugoslav scientists and researchers working in the fields of automatic control, system theory, and related areas. The first time, we met him at the Conference on System Sensitivity, Adaptivity, and Optimality held in Dubrovnik in 1964. He delivered lectures at the Institute "M. Pupin" in Belgrade several times on up-to-date developments in control theory. The last time he visited Yugoslavia as a guest of the XXXIII ETRAN Conference held in Novi Sad in 1989, where he delivered three lectures. Many trends in control theory have been initiated by seminal papers by Professor Tsypkin. Several Ph.D. thesis of our scientists have been inspired by Professor Tsypkin's visions.

Academician Ya.Z. Tsypkin was the member of editorial boards of the Scientific Review: Series Science and Engineering (the journal of Serbian Scientific Society) and Facta Universitatis: Series Electronics and Energetic (the journal of the University of Nis). The death of Professor Ya.Z. Tsypkin is a hard loss for the Russian and world science, for all his numerous friends and students. His Yugoslav friends and devotees will save bright memories on this exceptional and warmhearted man. Professor Ya.Z. Tsypkin left behind him his wife Olga (who was his spouse for about 60 years), his daughter Anna, his grandson Andrey, and great-grandson Dima.

Prof. M.R. Stojic