Fritz John was a mathematician whose major areas of study were partial differential equations, continuum mechanics, wave propagation analysis, and geometry.
He conducted research in various areas of pure and applied mathematics, including improperly posed problems. He formulated one of the basic criteria in the theory of optimization, and was one of the pioneers in systematically applying the Radon transform to questions in analysis. John’s interests included the singular behavior of solutions of partial differential equations. His work also dealt with the propagation of acoustic and elastic waves of finite amplitude. He was the author of Plane Waves and Spherical Means (1955) and Partial Differential Equations (4th ed., 1982).
John was a professor emeritus of the Courant Institute of Mathematical Sciences of New York University. His awards included the George David Birkhoff Prize in Applied Mathematics (1973), the Senior U.S. Scientist Humboldt Award (1980) and the American Mathematical Society’s Steele Prize (1982). He received fellowships from the Rockefeller Foundation (1942) and the Guggenheim Foundation (1962, 1970).
John received a Ph.D. (1933) from the University of Göttingen.