Sōichi Kakeya
Native spelling: 掛谷 宗一
1886–1947
Japanese mathematician whose work included polynomial root bounds and integral equations. In 1917 he posed the needle-rotation problem that gave rise to Kakeya sets and, later, the modern Kakeya dimension conjecture.
Sōichi Kakeya (1886–1947) was a Japanese mathematician. The Institute of Statistical Mathematics records that he graduated from the Imperial University of Tokyo in 1909, held academic posts at Tohoku and Tokyo, and served as the Institute's first director from 1944 until his death in 1947. His work on bounds for roots of algebraic equations with positive coefficients became known as Kakeya's theorem; a series of papers on simultaneous integral equations received the Imperial Academy Prize.
In 1917 Kakeya posed a geometric question about the smallest area of a planar region in which a unit needle can be turned through a full rotation. That needle problem inspired the study of Kakeya sets. The modern Kakeya conjecture asks about the Hausdorff and Minkowski dimensions of sets containing a unit segment in every direction; it is a later problem, distinct from Kakeya's original minimum-area question.
Workplaces: Tohoku Imperial University, Tokyo Imperial University, Institute of Statistical Mathematics
Japan