| Fritz John | |
|---|---|
| Born | 14 June 1910 Berlin, Germany |
| Died | 10 February 1994 (aged 83) New York, USA |
| Nationality | United States |
| Fields | Mathematics |
| Institutions | University of Kentucky Ballistic Research Laboratory New York University |
| Alma mater | University of Göttingen |
| Known for | John's equation John ellipsoid |
| Notable awards | Birkhoff Prize (1973) Steele Prize (1982) |
Fritz John (14 June 1910 – 10 February 1994) was a German-born mathematician specialising in partial differential equations and ill-posed problems. His early work was on the Radon transform and he is remembered for John's equation.
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He studied mathematics from 1929 to 1933 in Göttingen where he was influenced by Richard Courant among others. With Hitler's rise to power in 1933 "non-aryans" were being expelled from teaching posts, and John emigrated from Germany and immigrated to England. From then until 1991, he never returned to Germany.
John published his first paper in 1934 on Morse theory. He was awarded his doctorate in 1934 with a thesis entitled Determining a function from its integrals over certain manifolds from Göttingen. With Richard Courant's assistance he spent a year at St John's College, Cambridge. During this time he published papers on the Radon transform, a theme to which he would return.
John was appointed an assistant professor at the University of Kentucky in 1935 and he emigrated to the United States becoming naturalised in 1941. He stayed at Kentucky until 1946 apart from 1943 to 1945 during which he did war service for the Ballistic Research Laboratory at the Aberdeen Proving Ground, Maryland. In 1946 he moved to New York University where he remained.
Throughout the 1940s and 1950s he continued to work on the Radon transform in particular its application to linear partial differential equations, convex geometry, and the mathematical theory of water waves. He also wrote on numerical analysis and ill-posed problems. His textbook on partial differential equations was much influential and was re-edited many times.
From the mid 1950s he started working on the theory of equilibrium nonlinear elasticity. He retired in 1981 but continued to work on nonlinear waves.
He received many awards during his career including the Birkhoff Prize in Applied Mathematics in 1973 and the Steele Prize in 1982.