Renowned Mathematician Kiyoshi Ito Has Died at 93

November 26, 2008

Internationally renowned mathematician Kiyoshi Ito has died of respiratory failure at age 93. His work, which centered on the study of random processes and Brownian motion, has applications in phenomena as varied as the diffusion of pollen in water and the fluctuation of stock prices.

Professor emeritus at Kyoto University, which he joined in 1952, Ito at various times also taught at Cornell University, Stanford University, and elsewhere.

Ito won fame for developing his theory of stochastic differential equations and the "Ito formula." His mathematical ideas, which first appeared in print in wartime Japan in 1942, laid the foundation for the Black-Scholes model for equity pricing. Along with applications in physics and biology, his ideas were used in the 1980s to formulate pricing mechanisms, making him "the most famous Japanese in Wall Street." He also did important work on Wiener chaos and Lévy processes.

"People all over realized that what Ito had done explained things that were unexplainable before," Daniel Stroock of the Massachusetts Institute of Technology told the New York Times.

Ito served as director of the Research Institute for Mathematical Sciences at Kyoto University from 1976 to 1979. After retirement from Kyoto University, he took a position at Gakushin University and retired from there in 1985.  He received Japan's highest honors, including the Medal of Culture of Japan, awarded three weeks before his death. He also received the Wolf Foundation Prize (1987), the Kyoto Prize (1998), and the Carl Friedrich Gauss Prize (2006).

The citation for the Kyoto Prize noted: "Dr. Ito is the father of the modern stochastic analysis that has been systematically developing during the twentieth century. This ceaseless development has been led by many, including Dr. Ito, whose work in this regard is remarkable for its mathematical depth and strong interaction with a wide range of areas. His work deserves special mention as involving one of the basic theories prominent in mathematical sciences during this century."

Source: New York Times, Nov. 23, 2008; Yomiuri Shimbun, Nov. 15, 2008; Japan Times, Nov. 15, 2008.