Hitoshi Ishii (石井 仁司 Ishii Hitoshi, born on 12 October 1947), a Japanese mathematician, who is specialized in partial differential equations.
He first studied physics and then mathematics at Waseda University with a master's degree in 1972 and a doctorate in 1975 with dissertation "偏微分方程式の初期値問題のLP可解性及び一意性" (translation: "Lp solvability and uniqueness of the initial value problem for partial differential equations").[1] He became an assistant professor at Chūō University in 1976 and in 1989 a full professor. In 1996, he became a professor at Tokyo Metropolitan University and in 2001, he became a professor at Waseda University. He studies nonlinear partial differential equations (PDEs) such as Hamilton–Jacobi equation, viscosity solutions of PDEs, optimal control theory, differential games, and evolution of surfaces.
mit Pierre-Louis Lions: Viscosity solutions of fully nonlinear second-order elliptic partial differential equations. Journal of Differential Equations, vol. 83, 1990, 26–78 doi:10.1016/0022-0396(90)90068-2
On uniqueness and existence of viscosity solutions of fully nonlinear second order elliptic PDE's. Communications on Pure and Applied Mathematics, vol. 42, 1989, 15–45 doi:10.1002/cpa.3160420103