Li Rui (mathematician)

Li Rui was a Chinese mathematician, born at Yuanhe, now Suzhou, on 8 December 1768 and dead on 30 June 1817, who produced commentaries on important Chinese mathematical works and discovered independently an equivalent version of what is known today as Descartes' rule of signs. He studied Cheng Dawei's Suanfa tong zong as a boy and later mathematics at the Ziyang Academy in Suzhou under its director Qian Daxin, and from 1795 he worked with Ruan Yuan in Hangzhou on the biographies of astronomers and mathematicians published in 1799. He wrote commentaries on works of Li Zhi and Qin Jiushao, found a lost copy of Yang Hui's Method of Computation in 1810, which he published in 1814, and in 1813 wrote the Theory of Equations of Higher Degree.