[O]ne of [the 47 ronin], Shigekiyo Matsumura, was the greatest Asiatic mathematician of his age, who in his work Sanso, published in 1663, calculated the length of one side of a regular inscribed polygon of 32768 or 215 sides, obtaining 0.000095873798655313483 and thence for the value of pi 3.141592648, which is accurate to seven places of decimalsone of them, Shigekiyo Matsumura, was the greatest Asiatic mathematician of his age, who in his work Sanso, published in 1663, calculated the length of one side of a regular inscribed polygon of 32768 or 215 sides, obtaining 0.000095873798655313483 and thence for the value of pi 3.141592648, which is accurate to seven places of decimals ...
Shigekiyo Muramatsu (村松 茂清, 1608–1695) published Sanso (算俎) in 1663. Muramatsu served Asano (浅野) family and possibly had a math institute in Edo [present Tokyo]. Muramatsu had only a daughter, and took Hidenao (秀直) into his family as a son-in-law [the daughter's husband]. Hidenao and his son Takanao (高直) joined the forty-seven ronin to cause the Akō incident. In Sanso, Muramatsu arranged idai [problems published in earlier Japanese mathematics books written without answers] by classifying them into different levels with consideration for ease of learning. In this book, he also showed the calculation of pi from the regular inscribed polygon of 32768 sides to correctly obtain the value 3.1415926. Thus, this book was the first in the mathematical calculation of pi in Japan. Sanso was republished in 1684 by the title of Sanposanso (算法算俎). This item [possessed by Kyoto University Library and presented in the exhibition] is the copy of this republication, but it is not clear if this is the one published in 1684. Inside the back cover, it is written that this was bought in September 8, 1857, in Asakusa-kuramae.
- "Pi and the 47 Ronin." Pat's Blog (September 5, 2009).
- The Catalog of the Exhibition "Wasan no Jidai (和算の時代, The Age of Japanese Mathematics),"edited by Kenji Ueno, Chapter 3, p 28, item 66 (Kyoto University Library, 2003) (In Japanese).
- "赤穂浪士 (Akō-rōshi)," Wikipedia, The Free Encyclopedia, Japanese edition (March 19, 2011, 10:23).
- "Forty-seven Ronin," Wikipedia, The Free Encyclopedia (23 April 2011, 05:32).
Notes added later
- The revised version of Ref. 1 with an addendum appeared: "More on Pi and the 47 Ronin," Pat's Blog (May 3, 2011).
- According to the Japanese Wikipedia page on Hidenao Muramatsu, Shigekiyo Matsumura had the middle name Kyūtaifu (九太夫) (the "middle name" was used as the daily nickname in those days of Japan), and he had a son. However, the son disappeared from home and was lost, so that Shigekiyo took Hidenao as a son-in-law.