Alexandre Chorin

Alexandre Joel Chorin was born Alexandre Joel Choroszczański in Warsaw, Poland, on June 25, 1938, into a Jewish family. His father was an industrialist and his mother was a judge. When Germany invaded Poland in 1939, his immediate family and three other relatives escaped through Lithuania and the Soviet Union and, after two years, reached the British Mandate of Palestine. The family changed its Polish surname to Chorin in Israel. He kept the French spelling of his first name, he later explained, to avoid confusion with another fluid mechanics researcher with a similar name.

In Palestine a distant relative introduced the five-year-old to mathematical puzzles, geometry and negative numbers and told him he should become a mathematician. By eight he had made that his goal, and two years later his school placed him in a program for gifted students. In 1950 the family moved to Switzerland, where his father had business dealings. Chorin did not want to live there and, having grown up hearing about the Holocaust and murdered relatives, later recalled that he felt doing homework was collaboration with the enemy. His grades suffered and he left his private school at the end of his junior year to take an equivalency examination.

Because his grades closed off pure mathematics, Chorin studied engineering at the École Polytechnique Fédérale de Lausanne (EPFL), a subject close to mathematics that also suited his interest in airplanes. He graduated with an engineering diploma in 1961. At Lausanne he took courses from the geometer Georges de Rham and became his grading assistant, and he later said, "To a very large extent, I owe the fact that I became a mathematician to de Rham."

In 1961 he returned to Israel and, instead of military service, was assigned to the Weizmann Institute of Science to work with Chaim Pekeris. He taught himself to program WEIZAC, Israel's first computer, on equations for ocean tides. In a chance encounter on the street with de Rham, he was advised to choose a graduate school in the United States, and in particular to study with Peter Lax at New York University's Courant Institute. He earned an MS in mathematics from NYU in 1964 and a PhD in 1966 with the thesis Numerical Study of Thermal Convection in a Fluid Layer Heated from Below, supervised by Lax.

Chorin's doctoral work answered a question from weather forecasters trying to predict thermal inversions, and to compute the dynamics he devised the artificial compressibility method for incompressible flow, published in 1967. As a Courant postdoctoral researcher he published the projection method in 1968, a way of solving the incompressible Navier-Stokes equations that separated the computation of velocity and pressure and turned the equations into a vast linked set of algebraic equations a computer could solve. Early engineering readers found it impossibly abstract, he recalled, but it became one of the foundations of computational fluid dynamics, used for aerodynamics, blood flow, atmospheric modelling and artificial heart valve design.

He stayed at Courant as a researcher, became an assistant professor in 1969 and associate professor in 1970. After a year at UC Berkeley as a Visiting Miller Professor, he joined Berkeley's mathematics faculty in 1972 as an associate professor and became a full professor in 1974. He was drawn by the chance to work with Berkeley engineers and helped build its applied and computational mathematics program. At Lawrence Berkeley National Laboratory he served as senior scientist in the Mathematics Group and helped make it a leading mathematics center of the Department of Energy.

In 1973 he introduced vortex methods for slightly viscous flow, including the random vortex method that remains widely used in computing turbulent flow. He wrote extensively on turbulence theory and, from 1996, collaborated closely with the Russian mathematician Grigory Barenblatt on turbulence scaling and turbulent boundary layers. In his later work he developed optimal prediction methods for reduced models and implicit sampling and implicit particle filters for data assimilation. In 2002 the University of California Regents named him a University Professor. He retired in 2013 but continued to research, program and give talks.

Chorin's first marriage produced a son, Ethan Chorin, who became a US Foreign Service officer, a scholar of Libya and the author of Benghazi: A New History. Ethan recalled childhood days in cafés near Washington Square Village, in Berkeley and in Geneva, where his father wrote equations longhand while scanning stacks of punch cards. Chorin later married Esther Brass-Chorin and had two stepdaughters, Daniela and Aviva Gilbert.

He spoke or read more than six languages, consumed books at a remarkable rate and read ancient Greek as a pastime. Colleagues noted interests ranging from classical Greek literature to Philip Glass's opera Einstein on the Beach, and he was an opera aficionado who enjoyed New York's opera companies during his Courant years. His Berkeley colleague Ole Hald walked with him most evenings for some 20 years when they lived a few houses apart. In October 2005 he visited his son in Libya and lectured at Garyounis University in Benghazi on the mathematics of sandstorms, and he later visited Ethan in Cyprus, Djibouti and Dubai.

Chorin described himself as a calculator rather than a prover of theorems, saying, "I don't prove things; I calculate." He followed the method he learned from Chaim Pekeris: start with a concrete physics problem, apply mathematics, program it and get an answer. He was modest about his classroom teaching, saying he spoke too fast and covered too much material, though students remembered him as an excellent lecturer.

Berkeley described him as a staunch advocate of academic freedom and human rights who supported causes related to peace in the Middle East. The Simons Foundation called him a peacenik in matters of Israeli politics and recounted how he once tried to persuade a Palestinian father that it was fine for his son to write a thesis with an Israeli supervisor.

Chorin's projection method, artificial compressibility method and vortex methods are standard tools of computational fluid dynamics, and his approaches are used to design cars, aircraft, wind turbines, combustion engines and artificial heart valves and to build climate models. The Simons Foundation credited him with helping the field evolve from treating the computer like a huge abacus to routinely solving problems once considered hopelessly complex.

His mentoring was equally central to his legacy. He supervised about 50 doctoral students, including Phillip Colella, Charles Peskin and James Sethian, three of whom were elected to the National Academy of Sciences. Sethian called him "the perfect thesis advisor", and colleague Sunčica Čanić said his work established fundamental connections between mathematical analysis, probability and scientific computing.

National Academy of Sciences Award in Applied Mathematics and Numerical Analysis (1989). Norbert Wiener Prize in Applied Mathematics of the AMS and SIAM (2000). University Professor of the University of California (2002). Honorary doctorate, Technion Israel Institute of Technology (2003). Honorary doctorate, EPFL (2005). UC Berkeley Sarlo Distinguished Graduate Student Mentoring Award (2008). ICIAM Lagrange Prize (2011). National Medal of Science (2012 laureate, presented by President Barack Obama in 2014). Member of the US National Academy of Sciences; fellow of the American Academy of Arts and Sciences, the Society for Industrial and Applied Mathematics and the American Mathematical Society.

Books: A Mathematical Introduction to Fluid Mechanics, with Jerrold E. Marsden (Springer, Texts in Applied Mathematics; third edition 1993); Vorticity and Turbulence (Springer, 1994); Stochastic Tools in Mathematics and Science, with Ole H. Hald (Springer; third edition 2013).

Key papers include A numerical method for solving incompressible viscous flow problems (Journal of Computational Physics, 1967), Numerical solution of the Navier-Stokes equations (Mathematics of Computation, 1968), Numerical study of slightly viscous flow (Journal of Fluid Mechanics, 1973), Optimal prediction and the Mori-Zwanzig representation of irreversible processes (PNAS, 2000, with Hald and Kupferman) and Implicit sampling for particle filters (PNAS, 2009, with Xuemin Tu).

In 2014 the Simons Foundation released a filmed conversation with Chorin in its Science Lives series, with his former student James Sethian as listener, covering his early life, the Courant Institute, the projection and vortex methods, turbulence and teaching at Berkeley.

Alexandre Chorin died on October 19, 2026, at the age of 88. His son Ethan wrote that in recent years his father had lost his memory, and that his favourite phrase of love, "beyond all measure", gradually became "with large measurement" and finally just "measure". The place and cause of death have not been made public.

Ethan Chorin published a remembrance on October 26, 2026, and UC Berkeley's College of Letters and Science and Department of Mathematics published tributes on October 27, 2026. The SIAM Activity Group on Dynamical Systems also marked his death. He was survived by his wife, Esther Brass-Chorin, his son Ethan, and stepdaughters Daniela and Aviva Gilbert. Funeral or memorial arrangements have not been made public.