Yoshihiro Kurushima

Japanese: 久留島義太 - くるしま・よしひろ

Year of death: 29 November 1758 (8 January 1758)
Year of birth: Unknown A Japanese mathematician in the mid-Edo period. He studied mathematics by himself, and was discovered by Nakane Genkei while teaching mathematics in Edo. In 1730 (Kyoho 15), he served Naito Masaki, the lord of the Taira domain, and in 1747 (Enkyo 4), when Naito was transferred to Nobeoka, he went there for about six years. He loved sake and shogi, and was a man of many eccentricities, but his originality as a mathematician more than made up for his unconventional personality. Kurushima himself had no intention of leaving behind any mathematical drafts, so his achievements can only be seen from the few manuscripts collected by his disciples such as Yamaji Nushi. He is known not only for developing the most cutting-edge theory of circles at the time, but also for his work on extreme value problems, Laplace expansions of determinants, magic squares, and Euler functions in number theory. He had a close relationship with Matsunaga Ryosuke, and it is believed that Matsunaga's writings were greatly influenced by Kurushima. He also created tsumeshogi puzzles. <References> The Japan Academy, ed., History of Mathematics in Japan before the Meiji Period, Vol. 3; Kato Heizaemon, The Achievements of Kurushima Yoshita

(Kenichi Sato)

Source: Asahi Japanese Historical Biography: Asahi Shimbun Publications Inc. About Asahi Japanese Historical Biography

Japanese:

没年：宝暦7.11.29(1758.1.8)
生年：生年不詳
江戸中期の和算家。独学で数学を修め,江戸で数学指南をしていた折に中根元圭に見いだされる。享保15(1730)年平藩主内藤政樹に仕え,延享4(1747)年に内藤氏が延岡に移封された際には同地に6年間ほど赴いている。酒と将棋を愛し,奇行の多い人だったが,その破天荒な性格を補って余りあるほどの独創的な数学者であった。久留島自身に数学の草稿を残す意図は皆無だったので,山路主住のような弟子達が集めたわずかな遺稿でしか彼の業績はうかがえない。当時最先端の円理を発展させただけでなく,極値問題,行列式のラプラス展開,魔方陣,整数論のオイラー関数などの仕事が知られている。松永良弼との間には親密な交流があり,松永の著書には久留島の影響が多分にあると考えられている。詰将棋の創作もした。<参考文献>日本学士院編『明治前日本数学史』3巻,加藤平左衛門『久留島義太の業績』

(佐藤賢一)

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