By Kurt Helmes and Richard Stockbridge
Raymond Rishel, an internationally renowned scientist in the area of stochastic control, passed away on July 10, 2021, in Lexington, Ky. He was 91 years old.
Ray was born on June 27, 1930, in the small town of Phillips, Wis. He graduated from high school in 1948 and earned his bachelor’s degree in mathematics from the University of Wisconsin–Madison in 1952. After serving in the Army, Ray returned to UW–Madison and obtained his Ph.D. in 1959 under the supervision of Laurence Chisholm Young. His dissertation was titled “Area as the Integral of the Lengths of Contours.” Ray’s education and training in the calculus of variations, his applied work in industry—ranging from the guidance of missiles to the analysis of telecommunication networks—and his keen interest in combining theory with applications provided the foundation for his many accomplishments in the broad area of stochastic control.
After graduating with his Ph.D., Ray accepted a position in the Department of Aerospace at the Boeing Company in Seattle, Wash. He later relocated to New Jersey to work at Bell Labs before ultimately pursuing academia and joining the faculty at the University of Kentucky (UK) in the early 1970s as a professor of mathematics. He remained at UK for the rest of his professional career. Ray was an expert in stochastic control, specifically the control of partially observed and adaptive jump Markov processes and their applications to different fields in engineering, operations research, and financial mathematics. At UK, he built a strong research group in stochastic control, maintained a special research seminar for more than two decades, and served as director of the Operations Research program for many years.
Ray was both directly and indirectly supportive of the younger faculty members whom he attracted to the university and was a critical influence in their early and later successful careers. He also inspired several generations of researchers and practitioners in the field of stochastic control through his theoretical work and a well-received monograph that was published in 1975: Deterministic and Stochastic Optimal Control, co-authored with Wendell Fleming.
Due to his upbringing on a small farm in northern Wisconsin, Ray was very disciplined in his approach to work and life in general. He was a strong supporter of public education and valued the opportunities that it provided him, believing that everyone with talent should be given similar chances. Beyond academia, Ray was an outdoor enthusiast who enjoyed activities like hiking, mountaineering, and downhill and water skiing. He was especially proud of summiting Mount St. Helens twice before its eruption in 1980. Unfortunately, he had to stop short of the summit of Popocatépetl in Mexico in February 1982; according to Ray, mathematician Václav "Vic" Beneš made it to the top that day.
Ray is survived by his four children and 10 grandchildren, and was preceded in death by his wife Midge of 55 years. He will be greatly missed by friends and colleagues alike.
Kurt Helmes was formerly a professor at Humboldt University of Berlin and was a member of Ray Rishel's research group from 1985 until Ray’s retirement in 1998. Richard Stockbridge is a distinguished professor at the University of Wisconsin–Milwaukee. He was a member of Ray Rishel's research group from 1988 until 1998.