Editorial, Automatica, May 1998, Volume 34, No. 5


This obituary also appears in the April, 1998, issue of the IEEE Transactions on Automatic Control.

In Memoriam

Yakov Zalmanovitch Tsypkin

September 19, 1919 - December 2, 1997

A Life in Feedback Control

On December 2, 1997, the control society worldwide lost a legend in our field with the untimely death of our colleague, friend, and mentor, Yakov Zalmanovitch Tsypkin.

During his lifetime, Yakov Tsypkin received many well deserved awards as will be mentioned later. However the one he always cherished is the ASME Rufus Oldenburger Award. Upon receiving this award, he presented a lecture on "My Life in Feedback, and Feedback in My Life.'' Thus it is appropriate to choose the above title. I believe he would look with favor on this choice.

Since World War II, our field of control has gone through a
revolution in the development of many areas of research, important and significant applications, and new innovations in teaching methods. Yakov Tsypkin has been part of this revolution by playing an important role as a pioneer in these developments. The control society worldwide owes much to his talents and many contributions, and his life in feedback control will forever be remembered with affection by those who knew him and with admiration by those who are acquainted with his work.

During the last five decades, Yakov Tsypkin has published over three hundred scientific papers and twelve books which span the whole spectrum of new research in the field of control and related disciplines. Though each of these papers brings to light a new result, it is pertinent to mention the following papers which are of classical nature and will always shine as pioneering research endeavors.

In 1946, Tsypkin published his classical paper on feedback systems with delay. It is a major extension of the Nyquist criterion in which the problem of delay was solved in a single stroke simply and elegantly. An English translation of this paper was published in a volume in commemoration of Harry Nyquist edited by MacFarlane [1]. It is fitting that this paper appeared immediately following that of Nyquist's original paper. It is also quite deserving that both Nyquist and Tsypkin received, in different years, the ASME Rufus Oldenburger Medal} for their contributions to control. The method of Tsypkin is of major significance considering that the analytical formulation of the problem of stability with delay is very complicated.

The second piece of pioneering research of Yakov Tsypkin is in the area of pulsed (sampled-data) systems. He is considered to be the father of pulsed systems in the East. In a series of papers in 1949 and 1950, he extensively developed the discrete Laplace transform (z-transform and modified z-transform) which he applied to the study of pulsed systems. This work culminated in his classic book in this field in 1958. Another contribution to this field is known as the Tsypkin criterion. It is the discrete analog of Popov criterion and represents a sufficient stability criterion for nonlinear pulsed systems. This criterion has found many applications especially in digital filters and signal processing.

The third piece of pioneering work of Yakov Tsypkin is in relay control systems. Based on his research on delay and sampled-data systems, his research in relay control systems followed naturally. In this area he developed what is now well known as the Tsypkin locus. It is a graphical frequency domain technique for the study of forced oscillations in closed-loop relay control systems. In this technique he showed how the describing function method, in certain cases, can lead to incorrect results. His research in this field culminated in the publication of a classical book on relay control in 1955. Its English translation appeared in 1984.

The fourth area of research in which Yakov Tsypkin made pioneering contributions is in adaptive and learning automatic systems. Around 1965, he presented a brilliant and groundbreaking paper at the All Union Conference in Automatic Control in Odessa. In this paper he expounded, for the first time, a unified feature of separate fields (such as, pattern recognition, filtering, adaptive control, system identification, learning systems, and others) based on a nonlinear recursive difference equation. With this formulation various optimal and robust algorithms were developed for the design of adaptive control systems. This work was published in 1971 in the book Adaptation and Learning in Automatic Systems. While the earlier mentioned papers were mainly based on frequency domain methods, this one was based on minimization of certain nonlinear functions.

The fifth piece of pioneering research of Yakov Tsypkin is what should be known as the Michailov-Tsypkin-Polyak criterion. During the last decade, after the publication of Kharitonov's classical papers, widespread research activities on robust stability were initiated. While most of the proposed methods are analytical in nature, Tsypkin, in collaboration with a colleague and former doctoral candidate Boris Polyak, approached this problem with a graphical method based on the 1938 paper of Michailov. This approach based on a frequency domain diagram opened up a whole new method for the study of robustness.
As in the former pioneering works, this method is both simple and elegant. Many related papers were published by Tsypkin and Polyak during the last decade. In 1992, in an interview with C. C. Bissell [2] Tsypkin indicated the following: "For a long time the frequency domain took a back seat in modern control. I have always felt personally that frequency response methods were somehow the `natural' approach to control problems.'' He was correct, and he has shown that this approach is indeed the "natural" one.

Yakov Tsypkin has also contributed significantly as an educator. He is a founder of a scientific school which has graduated dozens of doctoral candidates. Many of them have become prominent in research, education, and professional activities in the former Soviet Union as well as in other countries. One of our distinguished control scientists Peter Kokotovic was a doctoral candidate cosponsored by Tsypkin.

Yakov Tsypkin was an excellent teacher and an effective expositor in explaining the many difficult concepts in a simple manner. His books, which have been translated to many languages, have been used in the education of many generations of control scientists.

Yakov Tsypkin was an effective administrator as well. He was the Chairman of the Russian Committee of Automatic Control and Vice-Chairman of the Publication Committee of the IFAC as well as a member of the editorial boards of several international scientific journals.

For all the above contributions, he was recognized through many awards from all over the world. Among these are the Laureate of Lenin and Andronov Prizes, the Quazza Medal of IFAC, and the Sir Harold Hartley Medal of the London Institute of Measurement and Control. In the U.S.A., he was elected an IEEE Fellow, received the prestigious ASME Rufus Oldenburger Medal as was mentioned earlier, and on his 60th birthday on September 19, 1979, in Moscow, I had the privilege and honor to present him the IEEE Automatic Control Society's Citation. At the time of his passing, he was a member of the Russian Academy of Sciences (Academician).

Yakov Tsypkin was born in the city of Dnepropetrovsk in the former U.S.S.R. and now Ukraine on September 19, 1919. He graduated from the Moscow Electrical Engineering Institute of Communication in 1941. He served in the Red Army as a parachutist during World War II. In the forties, he joined the A.A. Andronov (who is considered the Father of Control in U.S.S.R.) Seminar and Group at the newly established Institute of Automation and Remote Control in Moscow (now known as the Institute of Control Sciences). This group included such distinguished scientists as Aizermann, Meerov, Lerner, Goldfarb, Gantmacher, Feldbaum, and others. In 1950 he became a Senior Scientific Researcher, and since 1956 he became the Chief of a laboratory where he attended the last day of his life.

He is survived by his beloved wife Olga who was his spouse for 57 years, his daughter Inna, his grandson Andrey, and his great-grandson Dima.

I wish to end this memorium on a personal note. I knew Yakov Tsypkin as a colleague, friend, and coauthor for the last 40 years. During this period we communicated continuously and I have had our correspondence bound in four volumes, one each for the following periods - 1958-1968, 1968-1978, 1978-1988, and 1988-1997. [One copy of these volumes is in the Department of Electrical and Computer Engineering, University of Miami, Coral Gables, FL 33124, USA, and another copy is in the Institute of Control Sciences, Russian Academy of Sciences, Moscow, Russia.] His loss is a tragic one for myself, his family, as well as I believe for all who knew him. He is not only known as a great scientist and educator,
but also as a generous, charming, kind, and considerate person. We all mourn with great sorrow his passing, but are very grateful for his life on this earth.

The writer acknowledges the aid of Boris Polyak in providing Tsypkin's personal data and photograph.

Department of Electrical and Computer Engineering
University of Miami
Coral Gables, Florida 33124 USA

[1] MacFarlane, A.G.J. (Editor), Frequency Response Methods in Control Engineering (IEEE Press, New York), 1979; Tsypkin's paper "Stability of linear systems with delayed feedback,'' pp. 45-46.

[2] Bissell, C. C., "Yakov Tsypkin, A Russian Life in Control,'' IEE Review (IEE Press, London, UK), pp. 313-316, Sept. 1992.