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Klara Dan von Neumann (1911–1963)

Basic Facts

  • Full name: Klari Dan (born Klara Dan; later Klara Dan von Neumann)
  • Born: 18 August 1911, Budapest, Hungary
  • Died: 10 November 1963, La Jolla, California
  • Cause of death: Suicide by drowning (walked into the surf; coroner ruled it suicide)
  • Noted as: One of the first computer programmers; first woman to execute modern-style code on a computer

Family Background

Born to wealthy Jewish parents Karoly Dan and Kamilla Stadler in Budapest. The family was well-connected socially and hosted lavish parties. At age 14, Klara became a national champion in figure skating. She graduated from Veres Palne Gimnazium in Budapest in 1929.

Education

Klara had relatively little formal mathematical education. Her later description of herself as a “housewife” on immigration papers to the United States belied the technical skills she would develop. She was essentially self-taught as a programmer, learning through hands-on project work rather than formal training.

Four Marriages

First Marriage: Ferenc Engel (1931–1936)

Met Engel at one of her parents’ parties. At 19, she described herself as “frighteningly in love,” but his gambling addiction led to divorce.

Second Marriage: Andor Rapoch (1936–1938)

An investment banker 18 years her senior. Married only one month after her first divorce. The marriage was short-lived.

Third Marriage: John von Neumann (1938–1957)

She met John von Neumann at a casino in Monte Carlo, where he “explained that he had perfected a way to ensure that he would win roulette every time, but promptly lost all his money” and asked her to buy him a drink. Both underwent divorces from their respective spouses, and they married on 17 November 1938. They emigrated together to Princeton, where Klara initially listed her profession as “housewife.” John died of metastatic cancer on 8 February 1957.

Fourth Marriage: Carl Eckart (1958–1963)

In 1958, a year after John’s death, she married oceanographer and physicist Carl Eckart and moved to La Jolla, California.

Computing Career

Early War Work

After Pearl Harbor, Klara secured the position of “Head of Statistical Computing Group” at Princeton, her first foray into computational work.

ENIAC Weather Forecast (1950)

Klara played a central role in the ENIAC Meteorology Project, the first computer-generated weather forecast. She worked alongside the meteorology team led by Jule Charney, Agnar Fjortoft, and John von Neumann. In the published research paper, the authors thanked “Mrs. K. von Neumann for instruction in the technique of coding for the ENIAC and for checking the final code.”

She worked for 32 days on the project, managing 100,000 punch cards and ensuring there was no data loss. (Note: A 2021 Smithsonian correction clarified that Klara was not necessarily present for the entirety of the punch-card work; her primary contribution was writing and checking the code and training the meteorologists to program the ENIAC.)

Monte Carlo Simulations (1947–1948)

In April 1948, a team including John and Klara von Neumann and Nick Metropolis ran the first computerized Monte Carlo simulations on ENIAC. These were not only the first Monte Carlo calculations by computer but also the first code written in the modern stored-program paradigm ever to be executed. Klara wrote the code for the first computer simulation of the Monte Carlo method – the method now used in everything from election forecasting to epidemiological modeling.

H-Bomb Simulations

She and her team discovered they had been “testing the conveniency of the H-bomb” – the ENIAC calculations were being used for thermonuclear weapon feasibility studies.

MANIAC I Programming

After the war, Klara joined von Neumann in New Mexico to program MANIAC I (Mathematical Analyzer, Numerical Integrator, and Automatic Computer Model I) at Los Alamos Scientific Laboratory. The machine was designed by her husband and Julian Bigelow. She wrote the first programs for MANIAC I.

Life After John’s Death

John von Neumann was diagnosed with metastatic cancer in 1955 and died on 8 February 1957 at Walter Reed Army Medical Hospital. Klara witnessed his agonizing decline – the cancer spread to his brain, and he was kept under military security at the hospital.

In 1958, she married Carl Eckart and moved to La Jolla, California.

Death

On 10 November 1963, Klara “walked into the surf and drowned” at La Jolla. The coroner ruled it suicide. She was 52 years old.

Unfinished Autobiography

Among the von Neumann papers is Klara’s unfinished memoir titled “A Grasshopper in Very Tall Grass.” The title reflects deep insecurities evident in her correspondence despite her obvious intelligence and talent.

Posthumous Recognition

  • 2017: The Smithsonian Magazine published “Meet the Computer Scientist You Should Thank for Your Smartphone’s Weather App” by Sarah Witman (16 June 2017), bringing wide public attention to Klara’s contributions. (The article was later updated in May 2021 to more accurately reflect her role.)
  • 2022: Klara became the subject of Season 2 of the Lost Women of Science podcast, which examined her life and contributions in detail.
  • Finding Ada Day (2021): Featured profile highlighting her role as a computer scientist.

Personal Characteristics

Klara was a vivacious, socially adept woman who had been a competitive figure skater and moved easily in Budapest’s high society. Her marriage to John von Neumann placed her at the center of Princeton’s intellectual social scene, where the couple hosted legendary weekly parties. Despite her accomplishments, she suffered from deep insecurity – her memoir title “A Grasshopper in Very Tall Grass” captures her sense of being overshadowed in a world of towering intellects.

Connections to Others in the Story

  • John von Neumann: Third husband; she coded programs for his computing projects (ENIAC weather forecast, Monte Carlo simulations, MANIAC I).
  • Julian Bigelow: Co-designer of MANIAC I, which Klara programmed.
  • Jule Charney: Led the meteorology team for which Klara wrote the ENIAC weather forecast code.
  • Herman and Adele Goldstine: Colleagues in the ENIAC/IAS computing world.
  • Nick Metropolis: Collaborated on the Monte Carlo simulations on ENIAC.

Sources