Celebration of Life

Dr. Tien-Yien Li (1945-2020)

Dr. Tien-Yien Li, who coined the term “chaos” in his seminal paper “Period three implies chaos” with Dr. James Yorke in 1975, had passed away peacefully on June 25, 2020, at the age of 75.

Li, of Hunan ancestry, was born in June 1945 in Sha County in the Fujian Province of China. At age three, he followed his parents to Taiwan, where he received traditional Chinese education. He earned his B.S. in Mathematics at the National Tsinghua University in 1968, as a member of the first graduating Mathematics class of the university since it reopened in Taiwan. After fulfilling the mandatory military service for one year, he came to the United States to pursue his love of Mathematics at the University of Maryland. He received his doctorate in 1974 under the guidance of Dr. James Yorke.

Li joined the faculty of the Department of Mathematics at Michigan State University in 1976 and was promoted to the rank of full professor in 1983. He received the honorary title of University Distinguished Professor in 1998. He retired as a University Distinguished Professor Emeritus in 2018 after spending 42 years at the University.

Despite his numerous ailments, Li had been a trailblazer in several important fields of Applied Mathematics and Computational Mathematics. One of his many monumental accomplishments is his paper with Yorke, “Period three implies chaos.” This paper has been cited more than 4800 times according to Google Scholar. It is the first to formally encapsulate the concept of chaos in the field of Mathematics, and was credited by Professor Freeman Dyson (IAS) as “one of the immortal gems in the literature of Mathematics” in the 2008 Einstein Lecture article “Birds and Frogs”. His proof of Ulam’s conjecture is yet another pioneering work in the computation of invariant measures of chaotic dynamical systems, which laid a foundation to the area of computational ergodic theory. Working with Kellogg and Yorke, Li's ideas and the use of numerical methods in computing Brouwer’s fixed point, opened up a new era in the research of the modern Homotopy Continuation methods. The breadth and depth of Li’s research with his collaborators as well as his students on the algebraic eigenvalue problem and multivariate polynomial systems, had made him known in the world as one of the leaders in these fields.

Li received numerous honors and awards during his academic career, such as the highly prestigious Guggenheim Fellowship in 1995, Michigan State University’s Distinguished Faculty Award as well as Frame Teaching Award in 1996, College of Sciences Distinguished Alumni Award of National Tsinghua University in Taiwan in 2002, Michigan State University College of Natural Science’s Outstanding Academic Advisor Award in 2006, and National Tsinghua University’s Outstanding Alumni Award in 2012.

Li supervised twenty-six Ph.D. dissertations in the general areas of Dynamical Systems and Numerical Analysis throughout his career. The challenges that he posed to his students, his ideas and approaches to Mathematics research, as well as his courage and spirit of overcoming obstacles, have and will continue to have profound impact on his students and colleagues.