A chain of 64 simulated masses was supposed to share its energy and settle toward equilibrium, but it nearly returned to its starting pattern. The machine-language code that exposed that behavior was written by Mary Tsingou Menzel, the mathematician and pioneering computer programmer who died at her Los Alamos home on August 27, 2026, at 97, according to Rivera Family Funerals & Cremations.

The surprise became the Fermi-Pasta-Ulam-Tsingou problem, a starting point for generations of work in nonlinear dynamics. A 2026 Communications Physics commentary described the 1953 Los Alamos experiment as the first numerical experiment and traced modern particle-based simulation back to Tsingou's code. Its argument stretched from that small chain of masses to the computational methods now used to model molecules, fluids, fractures and galaxies.

Tsingou was born in Milwaukee on October 14, 1928, to Greek immigrant parents. Part of her childhood unfolded in Bulgaria before the family returned to the United States in 1940. She earned a bachelor's degree in mathematics from the University of Wisconsin in 1951 and arrived at Los Alamos the next year to work as a human computer, carrying out calculations on mechanical machines. She later returned to school and received a master's degree in mathematics from the University of Michigan in 1955.

At Los Alamos, the new MANIAC I computer needed people who could turn equations into instructions. Tsingou and Mary Hunt became its first two exploratory programmers. The work bore little resemblance to modern coding: instructions were punched onto paper tape, memory was scarce, and even finding the sine of an angle required writing the individual operations. Tsingou moved between mathematics and machinery, reducing a physicist's equations to steps the computer could execute and then checking the output. With John Pasta, she also created an early computer-graphics display of a simulated explosion on an oscilloscope.

The experiment that attached her name to scientific history began with a nonlinear model of masses linked like a vibrating string. Rather than spread the initial energy evenly among the system's modes, the MANIAC calculation showed the energy returning close to where it began. The 1955 Los Alamos report named Enrico Fermi, John Pasta and Stanislaw Ulam as authors, while crediting Tsingou for the programming and computer runs. Her role was easy for later readers to miss.

The record eventually caught up with the work. In a 2008 Physics Today account, physicist Thierry Dauxois connected Mary Tsingou to M. T. Menzel, the name under which she and J. L. Tuck published a 1972 follow-up study. Dauxois urged researchers to add her initial to FPU. FPUT subsequently became the accepted name across much of the literature, placing the programmer beside the three men whose surnames had defined the problem for decades.

Tsingou's career continued far beyond MANIAC. She adapted as Los Alamos moved through IBM and Cray machines and into FORTRAN, worked on calculations for controlled thermonuclear research, and developed code used in designing magnets for a proton storage ring. She retired in 1991. The family notice described her Los Alamos life with Joseph L. Menzel, whom she married in 1958: daily swims, walks to the Mesa Public Library and lunches with the East Park Pool Lunch Ladies. Their two daughters, eight grandchildren and three great-grandchildren survived her.

Tsingou's name now appears whenever researchers write FPUT, but the substance runs deeper than the corrected acronym. The recurring energy pattern her program revealed remains a live scientific problem; the 1972 paper extended its study; and the practice of using code as an experimental instrument has spread across science. Those continuities preserve what her careful work made possible: equations set in motion, unexpected behavior made visible, and a programmer restored to the history she helped create.