# Klára Dán von Neumann

Klára Dán von Neumann (née Dán; 18 August 1911 – 10 November 1963) was a Hungarian-American mathematician, self-taught engineer and computer scientist, noted as one of the first computer programmers. She was the first woman to execute modern-style code on a computer. Dán made significant contributions to the world of programming, including work on the Monte Carlo method, ENIAC, and MANIAC I.

## Early life

Klára Dán, known as Klári to her friends and family, was born in Budapest, Hungary on August 18, 1911, to Károly Dán and Kamilla Stadler, a wealthy Jewish couple. Her father had previously served in the Austro-Hungarian Army as an officer during World War I, and the family moved to Vienna to escape Béla Kun's Hungarian Soviet Republic. Once the regime was overthrown, the family moved back to Budapest. Her family was wealthy, and often held parties where Dán would meet many different people from various stations in life.
At 14, Dán became a national champion in figure skating. She attended Veres Pálné Gimnázium [hu] in Budapest and graduated in 1929.

## Work

After their wedding, Dán and John von Neumann immigrated to the United States, where he held a professorship at Princeton University. Upon immigration, Dán listed her profession as "housewife". However, after the Attack on Pearl Harbor, more jobs for women opened up in the U.S. and Dán was able to secure a position at Princeton. Her title was "Head of Statistical Computing Group". In 1943, J. von Neumann moved to Los Alamos National Laboratory in New Mexico to work on calculations as part of the Manhattan Project. Dán remained at Princeton until 1946, working at the university's Office of Population Research. At this time, she was sharing an office with Adele Goldstein. Dán also enrolled in calculus at Princeton in 1947. Both Goldstein and Dán were then contracted to work in Los Alamos New Mexico in early summer of 1947.
And so, after the war, Dán joined von Neumann in New Mexico to program the MANIAC I machine, which could store data, designed by her husband and Julian Bigelow. This work was entirely novel, a feat that had never been completed before. Dán scored the job, however, due to the belief at the time that programming was menial work, similar to human computing, a job commonly held by women. For decades after this, society would devalue the work of programming, which ultimately allowed women to be a large part of the workforce. More specifically, Dán's job was to translate mathematical instructions into a language the computer could understand. To do this she would look up "codes" - numbers that correspond to instructions for the computer. This is the origin of the word "coder", and the birth of the modern code paradigm. This coding also required her to ask for sections of the machine to be rebuilt, as there was not a clear distinction between software and hardware at the time. She then worked on the ENIAC (Electronic Numerical Integrator and Computer) on a project with von Neumann to produce the first successful meteorological forecast on a computer. Dán designed new controls for ENIAC and was one of its primary programmers. She trained a group of people drawn from the Manhattan Project to store programs as binary code. During this time she also wrote the code for the first computer simulation of the Monte Carlo method, which is a method to store and analyze large quantities of data and make predictions on everything from elections to COVID-19 trend forecasting.
She taught the meteorologists how to program ENIAC where she managed 100,000 punch cards ensuring there were no data loss. She worked for 32 days on the project, where she saw through and checked the final code.
After her husband's death from cancer in 1957, Dán wrote the preface to his Silliman Lectures. The lectures were published in 1958 and later edited and published by Yale University Press as The Computer and the Brain. She also wrote an unpublished memoir entitled A Grasshopper in Very Tall Grass. In 2022, Dán was the subject of a multi-episode season of the Lost Women of Science podcast.

## Personal life

Dán met her first husband, Ferenc Engel at one of her parents' parties. They wed in 1931. Dán was 19 and described herself as "frighteningly in love". Engel was an avid gambler, and took Dán on many trips to casinos. They were at a casino in Monte Carlo when Dán met her future husband, John von Neumann, for the first time. He explained that he had perfected a way to ensure that you could win roulette every time, and promptly lost all his money trying to prove his point. Afterwards, he asked Dán to buy him a drink. It was a very consequential interaction for both of them, and would set the stage for their later romance. Eventually, after a particularly tumultuous trip through Southern Europe, Engel's gambling became too much of a problem for Dán and she divorced him. One month later she remarried, this time to Andor Rapoch in 1936. He was an investment banker 18 years her senior. Throughout their marriage, Dán maintained contact with John von Neumann, and eventually in 1938, after von Neumann went through a divorce, divorced Rapoch and married von Neumann soon after. With the start of World War II looming, Dán went back to Budapest to convince her parents and in-laws to leave the country. She left on a boat on August 30, 1939. Her father did not adjust well to leaving his home country and factory, and committed suicide soon after coming to the U.S. in 1939. In June 1942 Dán suffered a late-term miscarriage.
After John von Neumann's death, Dán married oceanographer and physicist Carl Eckart in 1958 and moved to La Jolla, California. She died in 1963 when she drove from her home in La Jolla to the beach and walked into the surf and drowned. The San Diego coroner's office listed her death as a suicide.
Dán's step-daughter, Marina von Neumann Whitman, a prominent economist who is now retired, currently resides in Concord, Massachusetts.