Mary Tsingou

Mary Tsingou (later Mary Tsingou-Menzel) was born on 14 October 1928 in Milwaukee, Wisconsin, to Greek immigrant parents from Bulgaria, Thomas John Tsingou and Anastasia Koutsouyianni. Greek was spoken at home. After the Great Depression, the family spent several years in Bulgaria (Assenovgrad area) and returned to the United States around 1940 as war spread in Europe. She relearned English, skipped grades, attended West Division High School in Milwaukee, then studied mathematics and education at the University of Wisconsin, earning a bachelor's degree in 1951. Teaching posts for women were scarce as veterans returned, so a professor steered her toward Los Alamos, which was recruiting women mathematicians during the Korean War. After a security clearance delayed by her years in Europe, she arrived at the Laboratory on about 7 January 1952.

She began in Theoretical Division as a hand computer using Marchant calculators, then transferred to program MANIAC (Mathematical Analyzer, Numerical Integrator, and Computer), becoming one of the first programmers alongside Mary Hunt (later Kircher). Machine language, punched paper tape, tiny memory, and hexadecimal output made coding exacting. Her early training problem, computing the sine of an angle, ran correctly on the first try, a rarity she later joked she never repeated. With John Pasta and Stanislaw Ulam (and with Enrico Fermi's theoretical framing during summer visits), she designed and coded the nonlinear vibrating-string simulation that became Los Alamos report LA-1940, "Studies of Nonlinear Problems" (May 1955). The front matter listed work done by Fermi, Pasta, Ulam, and Tsingou; a footnote thanked "Miss Mary Tsingou" for efficient coding and running the MANIAC computations. Energy did not thermalize as expected. The surprise recurrence helped birth nonlinear science, soliton studies, and a path toward chaos theory, and is now widely called the Fermi-Pasta-Ulam-Tsingou (FPUT) problem.

She left briefly for a master's in mathematics at the University of Michigan (1955), returned to MANIAC II and later IBM, Cray, and related systems, and became an early Fortran expert. She coauthored follow-up FPUT work with James L. Tuck (1972). In later decades she worked on Controlled Thermonuclear Reactor efforts, Accelerator Group projects, Poisson Group magnetic-field codes, and proton-storage-ring calculations tied to Strategic Defense Initiative ("Star Wars") studies. Colleagues later noted that parts of the Poisson tooling remained relevant into the 2020s. She retired in 1991.

On 27 April 1958 she married Joseph Lawrence Menzel in Milwaukee. He worked in Los Alamos protective forces / AEC security and died on 7 January 2022 aged 98. They had two daughters who became physicians, Dr. Ann Menzel (John Charney) of Pittsburgh and Dr. Carol Menzel of San Antonio. Her sister Sally Peavy (Sally Tsingou), predeceased, was also an early programmer (Bureau of Standards / SEAC). After retirement Mary and Joe embraced Los Alamos daily life: swimming, library walks, and community lunches.

For decades she was the "mysterious lady" in the FPU footnote. Thierry Dauxois's 2008 Physics Today essay argued for renaming the problem FPUT. Los Alamos National Security Science magazine's 2020 profile "We thank Miss Mary Tsingou" and Scientific American's 2021 feature amplified that recognition. She remained characteristically modest: credit for the programming had been acknowledged, she said, and the name itself "didn't matter." Looking back she observed that mid-century hopes had centered on nuclear energy, "but it's the computers that have changed the world."

Mary (Tsingou) Menzel died peacefully at home in Los Alamos on 27 August 2026, aged 97, following a short illness (not further detailed publicly). A memorial service is scheduled for Monday 21 September 2026 at 11 am at Rivera Family Funeral Home of Espanola, New Mexico, with a light reception afterward. A private family burial will follow at Santa Fe National Cemetery, where she will be interred with her husband. Memorial donations may be made to the Betty Ehart Senior Center in Los Alamos.