SUBJECT:

Passing of Emeritus Professor of Mathematics Ronald K. Getoor

Ronald Kay Getoor, professor emeritus in the Department of Mathematics at UC San Diego, died peacefully at his home on Oct. 28, 2017. He was 88.

Getoor was born in Royal Oak, MI, on Feb. 9, 1929. He attended the University of Michigan where he received an A.B. in Mathematics in 1950, an M.S. in Mathematics in 1951 and a Ph.D. in Mathematics in 1954 under the direction of Arthur H. Copeland. Getoor spent two years between 1954 and 1956 at Princeton University as a Fine Instructor, a position named in honor of Henry Burchard Fine, who established Princeton as a leading center for mathematics in the early part of the 20th century. At Princeton, Getoor met William Feller, Kiyoshi Itô and Henry P. McKean, Jr. (then Feller's student). Itô had a profound impact on Getoor, influencing the direction of his research in the years that followed. Getoor was appointed assistant professor at the University of Washington in 1956, arriving in the same year as his future collaborator Robert M. Blumenthal. Getoor had advanced to full professor by the time he moved south to the nascent Mathematics Department at UC San Diego in 1966. He spent the rest of his career at UC San Diego, achieving the highly distinguished rank of Professor Above-Scale. Although he formally retired in 2000, he continued an active research program until 2010. Getoor visited various other institutions over the years, including MIT in 1959-60 under an NSF postdoctoral fellowship and Stanford University on a sabbatical.

Getoor was a leader in the growth of Probability Theory that began in the 1950s and continues to this day. His career spanned more than 50 years, and during that time he focused on the study of stochastic processes, principally Markov processes. In the late 1950s, Getoor and Blumenthal set out to understand the work of Gilbert Hunt on the connection between Markov processes and potential theory (extending the connections between Brownian motion and Newtonian potential theory that were known to Perron, Wiener, Kakutani and others). They succeeded in this mission, which resulted in the foundational book, "Markov Processes and Potential Theory," published in 1968. Offshoots of this program were illuminating and groundbreaking work on stable processes and on the local times of Markov processes. This work has had a lasting impact on the field, and it is frequently cited even today.

Shortly after moving to San Diego, Getoor started a long-term collaboration with Michael J. Sharpe, who joined the UC San Diego mathematics faculty in 1967. Their joint work covered an impressive stretch, from abstract results on general Markov processes to detailed investigation of the intricate behavior of Bessel processes. Perhaps the most important of this work was the influential paper "Conformal Martingales" and their extensive work on last-exit times and excursions. Starting in the early 1980s, Getoor became interested in the so-called Kuznetsov process, which is the stationary version of a given strong Markov process, with time extending to infinity in both directions. Such a process provides a probabilistic embodiment of the analytic duality relationship that was a cornerstone of the earlier work with Blumenthal. This path-wise view of "time reversal" became a key tool in Getoor's detailed studies of the excessive measures of a Markov process, some of which were conducted in collaboration with Patrick J. Fitzsimmons, and which culminated in Getoor's definitive monograph on the subject "Excessive Measures," published in 1990.

Over his career, Getoor published more than 100 research articles and three books. Getoor's writings are notable for their clarity of exposition and attention to detail. Getoor was elected a Fellow of the Institute of Mathematical Statistics in 1971, and was a member of the inaugural class of Fellows of the American Mathematical Society, in 2013. He was an invited speaker at the 1970 International Congress of Mathematicians (ICM) in Nice; the quadrennial ICM is where the Fields Medals are announced.

Getoor was a dedicated teacher and mentor who taught all levels of mathematics. He supervised the Ph.D. theses of nine students at UC San Diego, and he hosted several mathematics post-doctoral visits to campus. Along with Kai Lai Chung and Erhan Çinlar, he founded in 1981 the "Seminar on Stochastic Processes," a yearly gathering of "kindred spirits working on stochastic processes" with the aim of stimulating discussion and collaboration. The "Seminar" continues to this day.

As one of the senior members of the UC San Diego Department of Mathematics, Getoor helped shape the growth of the department and especially of the probability group. He was known within the department and around campus for his sage advice and was tapped to serve on the Academic Senate Committee on Academic Personnel (then called the "Budget Committee"). Once the faculty club opened in 1988, Getoor enjoyed lunching at Euclid's table with mathematics colleagues and mathematics buffs from around campus; he also helped advise the club by serving on its Board of Directors.

As a young man, Getoor was a competitive table tennis player and won a state championship. Throughout his life, he enjoyed the outdoors, including hiking, body surfing (particularly at Scripps, Torrey Pines and Del Mar), and he enjoyed road trips to wine country, the California and Pacific Northwest coasts, and to national parks. He was an avid fan of classical music and the opera, attending the San Diego Opera as a season subscriber for many years.

Getoor is survived by his second wife Anne Westbrook Getoor; his daughter Lise Getoor, who is a professor in the Computer Science Department at UC Santa Cruz; his brother Richard Getoor of Cincinnati, OH; his sister Jackie Kuthy of Fort Lauderdale, FL; stepchildren Thomas Westbrook and John Westbrook; step grandchildren Emma, Lilli, Marian and Philip Westbrook; and nieces and nephews including Donna Beshgetoor of San Diego.

Those wishing to honor Getoor's memory are asked to donate to the "Ronald Getoor Memorial Fund for Mathematical Probability Research at UC San Diego." Donations can be made online at http://bit.ly/GetoorMemorialFund. A memorial gathering will be scheduled at a later date for family, friends and colleagues.

Steven Boggs Dean Division of Physical Sciences Lei Ni Professor and Chair Department of Mathematics