In Control, Almost from the Beginning Until the Day After Tomorrow

I entered the field of control as a Ph.D. student in September 1965, over 40 years ago. A couple of years before, Roger Brockett and Michael Athans had joined the Electrical Engineering faculty ofMIT. They introduced Modern Control Theory, as the state space approach was called then, as a research activity and had set up a graduate curriculum in this area. In my first semester, I took courses on optimal control à la Pontryagin and on the state space theory of systems. This last course was given for the first time atMIT. On the West Coast of the US, similar courses existed already a few years earlier. Later, I taught this course myself many many times. It became my favorite subject. After my Ph.D., I joined the control group of the Electrical Engineering department of MIT as an assistant professor. I spent 5 years in that capacity, with a one-year leave of absence as a postdoc at the University of Cambridge in the UK. In 1973, I was appointed Professor of Systems and Control in the Mathematics department of the University of Groningen. In 2003, I became Emeritus. Presently, I am Guest Professor with ESAT (the department of Electrical Engineering) of the K.U. Leuven in Belgium. During my career, I had the privilege to serve as supervisor to a number of very talented Ph.D. students, ‘promovendi’, many of whom became important contributors to the field. The number of my Ph.D. students or postdocs at any time was never large, typically 2 or 3. With some of them, I discussed research almost on a daily basis. Working together with these young people has been an important part of my modus operandi of doing research. I also did my chores on the administrative level, as conference organizer, stints as head of my department, as president of the Dutch Mathematical Society and of the European Union Control Association. I was initiator of a graduate program (later called DISC) in Systems and Control on the national level in the Netherlands. I also did more than my share of editorial work, in particular as managing editor of SIAM Journal of Control for 5 years, and of Systems & Control Letters for the first 15 years of its existence. These professional ‘service’ contributions rate very high with the public. Nevertheless, I consider them as secondary to research and teaching. But I wouldn’t go as far as Paul Halmos, who in his authomathography calls (his) service activities a cop-out. Many personal experiences shaped my views on control, system theory, mathematics, and science, but the two dominating influences surely are: (1) my formative years as a Ph.D. student and a beginning researcher at MIT in the US, and (2) my 30 years as a mathematics professor in the Netherlands. In this article, I wish to make a few observations about the development of the field since the 1960s until now, as I experienced them personally. The research themes which I talk about are mainly those I was directly involved in. I am not a member of what one would call the first generation of researchers in modern control theory, but of the first generation of persons who were taught a full curriculum in the area. During my years at MIT, I had the good fortune to become personally acquainted and develop close professional relationships with many of the pioneers of the subject, among