## Obituaries: Eugene Isaacson

**July 10, 2008**

Eugene Isaacson, 1919–2008. Reprinted with permission from Mathematics of Computation, April 1989 (a special issue dedicated to Isaacson), American Mathematical Society.

Eugene Isaacson (1919–2008), professor emeritus at the Courant Institute of Mathematical Sciences, New York University, was one of the pioneers of modern numerical mathematics. Like most Jewish students of mathematics and physics of his age, he was a graduate of City College in New York. He entered the graduate program in mathematics at New York University and received his PhD, under K.O. Friedrichs, in 1949. He spent his academic career at Courant.

Isaacson's dissertation was on water waves on sloping beaches; in it, he derived an explicit formula for the solution of the case in which the angle of the slope is a rational multiple of pi. It turned out that Hans Lewy had also derived an explicit, but different, formula for the solution. Because the solution is unique, the two formulas must be equal for all rational numbers. Lewy showed that the equality of the two formulas implies the law of quadratic reciprocity.

Isaacson's subsequent research concerned the numerical solution of differential equations. *Analysis of Numerical Methods*, the book he wrote in collaboration with Herb Keller, was one of the leading texts of its time. Many of Isaacson's 15 PhD students became prominent in research on numerical methods.

In the mid-1950s the Atomic Energy Commission placed the supercomputer UNIVAC at the Courant Institute, to be used for research. One problem of the AEC on which Isaacson worked concerned the Grand Cooley Dam: If the dam were breached by sabotage, would the resulting flood wave on the Columbia River inundate the Hanford reactor? The AEC had originally asked the Army Corps of Engineers to consider the problem; the Corps was not up to the task, however, and so the Courant Institute was asked to do the calculation using the UNIVAC. Jim Stoker, an expert on water waves, did the mathematical formulation, and the numerical solution of the shallow water equation was accomplished under the leadership of Gene Isaacson. The answer to the AEC's question was that the Hanford reactor was safe. The Corps of Engineers subsequently adopted the numerical method developed by Isaacson.

Isaacson was editor of the journal *Mathematical Tables and Aids to Computation*, which later morphed into *Mathematics of Computation*.

Even after his retirement, until a couple of years ago Gene faithfully attended the seminar on numerical methods and the applied mathematics seminar at Courant.

An interview with Gene Isaacson is part of SIAM's oral history project, and can be found at http://history.siam.org/oralhistories/isaacson.htm. A movie, "The Mathematician and the River" is available from the Educational Testing Service.---*Peter Lax, Courant Institute of Mathematical Sciences, New York University.*