Sadasuke Fujita

A mathematician in the mid-Edo period. Also written as Sadasuke. Sometimes signed as Tōteiken. Commonly known as Hikotayū, later Gonpei, his pen name was Shichō, and his pen name was Yuzan. Born into the Honda family in Ozato-gun, Musashi Province (Saitama Prefecture), he was adopted by Fujita Sadayuki, a samurai of the Shinjō domain in Yamato (Nara Prefecture). He studied mathematics under Yamaji Nushizumi, and was recommended by Yamaji to become a samurai of the Arima domain in Kurume (Fukuoka Prefecture). With the support of the domain's lord, Arima Yoriyuki, he wrote the famous work Seiyō Sanpō (1781), which made him famous. He also compiled mathematical puzzles into Shinpeki Sanpō (1789). His many unpublished works include "Hensho" (1777) and "Igyo Dokai" (1781). A controversy arose over a mathematical tablet that Aida Yasuaki of the Saijo school had hung at Atago Shrine in Shiba, Edo, and a heated debate raged between the Seki and Saijo schools for over 20 years. His son, Kagen (1772-1828), also served the Arima family, and trained many disciples over two generations.

[Shimohira Kazuo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

江戸中期の数学者。定資とも書く。また滕定賢(とうていけん)と署名することもある。通称は彦太夫、のちに権平、字(あざな)は子證、号は雄山。武蔵(むさし)国大里郡（埼玉県）の本田家に生まれ、大和(やまと)（奈良県）の新荘藩士藤田定之の養子となった。数学を山路主住(やまじぬしずみ)に学び、山路の推挙で久留米(くるめ)（福岡県）の有馬(ありま)藩士となる。藩主有馬頼徸(よりゆき)の援助で名著『精要算法』（1781）を著し、世に知られる。また、算額の問題を集めて『神壁算法(しんぺきさんぽう)』（1789）をまとめた。刊行されなかった著書に『変商』（1777）、『異形同解』（1781）など多数がある。最上(さいじょう)流の会田安明(あいだやすあき)が江戸・芝の愛宕(あたご)神社に掲げた算額のことで論争となり、関流と最上流の間で20年以上もの間、激論が戦わされた。子息の嘉言（1772―1828）も有馬家に仕え、親子二代にわたり多くの子弟を養成した。

［下平和夫］

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