# IN MEMORIAM - Prof. Harry Dym

## Prof. Harry Dym utilized tools from classical analysis and operator theory to earn his place as a world-leading mathematician

Briefs

The Weizmann Institute’s Department of Mathematics mourns Prof. Emeritus Harry Dym, who passed away in July 2024 at age 86.

Born in Vienna in 1938 to Polish Jewish parents, Harry and his family escaped to England and emigrated to the United States in 1949. He earned his BSc in electrical engineering at the Cooper Union in New York, then moved to California with his wife, Irene, to begin graduate studies in electrical engineering at the California Institute of Technology. He completed his MSc there in 1960 and the Dyms moved to Boston, where he entered the private sector.

In 1963 he was accepted to the Massachusetts Institute of Technology under the supervision of Prof. Henry McKean, where he earned his PhD in 1965. The next year, he joined Prof. McKean at The Rockefeller University in New York, where fellow postdoc Moshe Kugler―later a tenured professor of physics at the Weizmann Institute―suggested that Harry apply to Weizmann, of which he had never heard. He accepted a postdoctoral position in the Department of Applied Mathematics. He described Rehovot as having a “certain rustic charm,” and the seed was planted for a future return.

In 1972, Prof. Dym came back to the Institute as a founding member of the Department of Pure Mathematics. He was awarded tenure in 1973, by which time his focus had shifted from probability to analysis. In 1988, he was named the first incumbent of the Renee and Jay Weiss Chair in Theoretical Mathematics.

Throughout his career, many of Prof. Dym’s research interests stemmed from theoretical problems that arise in electrical engineering design problems and are connected to the areas of signal processing and control. He devoted much of his time to investigations in interpolation theory—determining whether the desired characteristics of a system can be realized within prescribed boundaries—and inverse problems for canonical systems of integral and differential equations, employing tools from classical analysis, operator theory, and complex function theory.

He also lent his name to the Dym equation, an important early example of a family of nonlinear wave equation in which the mechanical law governing the wave propagation depends on the wave itself. While a marginal aspect of his work (in fact, Prof. Dym never published it), the equation continues to generate discussion and examination decades after it was introduced.

One of Prof. Dym’s long-time colleagues was the late mathematician Prof. Israel Gohberg, who immigrated to Israel from the former USSR in 1974. In 2002, Prof. Gohberg co-edited “The Harry Dym Anniversary Edition” of the journal Operator Theory: Advances and Applications, dedicated to Prof. Dym’s influence on this field and its applications, which opens with an autobiographical memoir by Prof. Dym, titled “Looking Back.”

In a tribute to Prof. Dym published in the same journal, Prof. Gohberg wrote, “I learned many things from Harry in mathematics and also in everyday life… I could ask his advice on any question without hesitation… There is a big difference between the USSR and the West in the evaluation of various areas of mathematics and mathematicians. Harry explained these things which looked like contradictions to me.”

After retiring, he continued to share his passion for mathematics by teaching at the Feinberg Graduate School and publishing papers and books in his areas of interest. In his last book, Prof. Dym wrote that after “some four score and five years of observing the human scene: those who think they know all the answers don’t know all the questions.”