### The passing of Saul Abarbanel

Saul Abarbanel passed away on December 29, 2017 in Tel Aviv, Israel. He was a frequent visitor to the Division of Applied Mathematics. Professor Abarbanel had just visited the Division for the Annual David Gottlieb Memorial Lectureship and Recital, which was held on October 16, 2017. He will be dearly missed.

The following paragraph is taken from: https://www.tau.ac.il/institutes/advanced/past_directors.html:

Saul Abarbanel was born 1 June 1931 in Montclair, New Jersey, USA. He grew up in Tel-Aviv and served in the IDF during the War of Independence (1948-1950). He then went to the United States for his university education and received all three degrees (B.Sc, M.Sc, PhD) from MIT. The first two were in Aeronautics and Astronautics and the doctoral dissertation in Theoretical Aerodynamics. He did his post-doctoral work at the department of Applied Mathematics at the Weizmann Institute of Science, Israel (1960-1961). He was then appointed Assistant Professor at MIT (1961-1964). In 1964 he was appointed Associate Professor and department head of Applied Mathematics at Tel-Aviv University and in 1970 promoted to Professor. He also served in succession as the Dean of Science, Vice Rector and Rector of Tel-Aviv University (1966 -1980). He was consultant to NASA and was Visiting Professor at various times at MIT, Brown and University of California, Berkeley. He served as Chairman of the National Research Council of Israel (1986-1993). He was awarded in 1992 the Scientific Achievement Award by NASA and is currently the IBM Distinguished Visiting Research Professor at Brown University. He was the Director of the Sackler Institute of Advanced Studies from 1997 to 2003.

The following historical paragraph describing Saul Abarbanel's research is taken from "The History of Numerical Analysis and Scientific Computing published by SIAM. (See http://history.siam.org/oralhistories/arbarbanel.htm)

Saul Abarbanel describes his work in numerical analysis, his use of early computers, and his work with a variety of colleagues in applied mathematics. Abarbanel was born and did his early schooling in Tel Aviv, Israel, and in high school developed an interest in mathematics. After serving in the Israeli army, he entered MIT in 1950 as an as an engineering major. He found himself increasing drawn to applied mathematics, however, and by the time he began work on his Ph.D. at MIT he had switched from aeronautics to applied mathematics under the tutelage of Norman Levinson. Abarbanel recalls the frustration of dropping the punch cards for his program for the IBM 1604 that MIT was using in 1958 when he was working on his dissertation, but also notes that this work convinced him of the importance of computers. Three years after receiving his Ph.D., he returned to Israel, where he spent the rest of his career at Tel Aviv University. He used the WEIZAC computer at the Weizmann Institute, and in the late 1960s worked on a CDC machine and an early transistorized Philco computer owned by the Israeli Army. Although Arbarbanel’s early work was more computational, his later work reflects his mid-career realization of the importance of theory in achieving practical results. He enjoyed his time at NASA’s Institute of Computer Applications to Science and Engineering (ICASE), which he believes served an important role by bringing together outstanding scientists and mathematicians and allowing them an opportunity to become better acquainted and to collaborate more extensively. Besides his extensive collaboration with David Gottlieb, Abarbanel worked with a variety of colleagues during his career, including engineers Earl Murman and Ajay Kumar. He discusses well- and ill-posed equations, and distinguishes ill posedness and instability from chaos. He believes that his training in engineering and aerodynamics gave him an advantage in doing applied mathematics. He thinks that today’s students in numerical analysis can benefit from exposure to the sciences and should receive training in a broad range of mathematical tools. He thinks that his work with David Gottlieb demonstrating that linearized Navier-Stokes equations can be symmetrized and highlighting problems of boundary conditions for infinite fields in electromagnetics as among his most significant contributions.