Systems and Control

Motivated by the emergence of the digital computer, a group headed by Professor John R. Ragazzini did seminal work on sampled-data systems (now known as “discrete-time systems”) and early digital control into the 1950s.

Professor Ralph J. Schwarz (Ph.D., 1949), later to become vice dean of the School of Engineering and Applied Science, began his affiliation with the department as a student in the 1940s and made major contributions to its activities throughout his career. Among the first group of doctorate recipients during the postwar period, almost all supervised by Ragazzini, were Ralph Schwarz, Lotfi A. Zadeh (Ph.D., 1949), Eliahu Jury (Eng.Sc.D., 1953), Gene Franklin (Eng.Sc.D., 1955), Bernard Friedland (Ph.D., 1957), Rudolph Kalman (Eng.Sc.D., 1957), and Jack Bertram (Ph.D., 1957). Jacob Millman, an expert in electronics, joined the group in 1952. Thomas E. Stern, an expert in nonlinear systems, joined our department in 1958.

That period became a veritable golden age of activities in systems and controls at Columbia. Through research publications and textbooks, this faculty group and their doctoral students influenced the development of modern electrical engineering much more than their number would suggest. Much of the classical theory of sampled-data control systems, now known as digital control, was developed at Columbia during the '50s. Jury was a key contributor to the application of z-transform techniques to sampled-data systems; in fact, the name “z-transform” originated at Columbia in 1952. He is also known for the “Jury stability test” for sampled-data systems. Zadeh, today known as the father of fuzzy logic, contributed pioneering work in the area of time-varying systems; in fact, his entire doctoral thesis consists of his seminal paper in that area. Kalman, today known for his landmark work on optimal filtering and control, was a key contributor to state-space methods while at Columbia; he campaigned actively for time-domain techniques, as opposed to the frequency-domain techniques then prevalent in the US. He argued, correctly, that time-domain techniques can easily be extended to nonlinear systems, whereas frequency-domain ones cannot. With his Columbia classmate, Jack Bertram, he originated the fundamental concept of controllability in systems theory.

Pioneering textbooks by Millman in electronics; by Ragazzini, Gene F. Franklin and Jury in sampled-data controls; and by Schwarz and Bernard Friedland in linear systems, made the work of this group known throughout the world.


  • B. Friedland, Control System Design – An Introduction to State-Space Methods, McGraw-Hill, 1985.
  • B. Friedland, private communication.
  • K. Premaratne, Eliahu I. Jury, IEEE Control Systems Magazine, February 2010, pp. 72- 77.