Kōsaku Yosida

Kōsaku Yosida was a Japanese mathematician, born in Hiroshima in 1909 and raised in Tokyo, who worked chiefly in functional analysis. He graduated from Tokyo Imperial University in 1931 and, from 1933 at Osaka Imperial University, was influenced by Mitio Nagumo and Shizuo Kakutani; his joint papers with Kakutani include the proof of a maximal ergodic theorem. His theory of semigroups, published in 1948 while he was at Nagoya, is now called the Hille-Yosida theory and was applied to diffusion equations, Markov processes, hyperbolic equations and potential theory. His books include Topological Analysis (1951) and the classic Functional Analysis (1965), which ran to six editions. He held professorships at Osaka and Tokyo, served as president of the Mathematical Society of Japan for seven terms, and received the Fujiwara Prize in 1964 and the Emperor's Prize of the Japan Academy in 1967. He died in Tokyo in 1990.