Yoshinori Isomura

A mathematician from the early Edo period. Nicknamed Kibei, and later Bunzo. He was a ronin of the Nabeshima clan of Hizen, and later became a samurai of the Oshu Nihonmatsu domain. As a construction magistrate, he laid water supply to Nihonmatsu Castle. His published work was Sanpo Ketsugisho (1659), which compiled all the mathematics that had developed since Jingoki, and was a compilation of the highest level of mathematics that can be done with abacus without using algebraic equations. In addition to providing solutions to the problems left behind in Jingoki, he also submitted 100 problems left behind. 25 years after the first edition, an expanded edition was published, which also included the answers to his own 100 problems left behind. He defeated the schools of Hatsusaka Shigeharu and Shibamura Moriyuki, and corrected errors in Hatsusaka's Enpo Shikanki and Shibamura's Kakuchi Sansho (both published in 1657) in his Sanpo Kekigi Sho. One of his works that has been passed down in manuscript form is Uinoko (around 1685). He seems to have had many disciples other than Murase Yoshimasu.

[Shimohira Kazuo]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

江戸初期の数学者。通称は喜兵衛、のちに文蔵。肥前の鍋島(なべしま)家を浪人し、のちに奥州二本松藩士となる。作事奉行(さくじぶぎょう)として、二本松城に水道を引く。出版された著書は『算法闕疑抄(さんぽうけつぎしょう)』（1659）で、『塵劫記(じんごうき)』以来発達してきた数学は本書にすべてまとめられ、代数方程式を使わないで珠算でできる最高度の数学が集大成されている。『塵劫記』の遺題に解答を与えるとともに、100問の遺題を提出している。初版から25年たって、増補版を出版した。なかに自分の遺題100問の解答も示している。彼は、初坂重春(はつさかしげはる)または柴村盛之(しばむらもりゆき)の塾を道場破りし、さらに、初坂の『円方四巻記』と柴村の『格致算書』（ともに1657年刊）の誤りを『算法闕疑抄』のなかで訂正している。稿本で伝わっている著書に『うゐの子』（1685ころ）がある。村瀬義益(よします)のほか弟子は多かったらしい。

［下平和夫］

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