Tuesday, July 9, 2013

Zu Chongzhi, Calculator of Pi

Zu Chongzhi, [Wade-Giles Tsu Ch’ung-chih]  (b. 429, Jiankang [modern Nanjing, Jiangsu province], China - d. 500, China), was a Chinese astronomer, mathematician, and engineer who created the Daming calendar and found several close approximations for pi.

Like his grandfather and father, Zu Chongzhi was a state functionary. Around 462 he submitted a memorandum to the throne that criticized the current calendar, the Yuanjia (created by He Chengtian [370–447]), and proposed a new calendar system that would provide a more precise number of lunations per year and take into consideration the precession of the equinoxes. His calendar, the Daming calendar, was finally adopted in 510 through the efforts of his son, Zu Geng.

Li Chunfeng (602–670) called Zu Chongzhi the best mathematician ever and gave him credit for three approximations of π: 22/7, 355/113, and the interval 3.1415926 < π < 3.1415927; the third result remained the best in the world until improved by the Arab mathematician al-Kashi (flourished c. 1400). Zu also worked on the mathematical theory of music and metrology, and he constructed several devices, such as a semi-legendary “south-pointing carriage” (most likely a mechanical device that kept a pointer in a fixed position); the carriage was topped by a symbolic figure that, once properly aligned, would always point to the south. None of his writings has survived.


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