A lifelong friendship and fruitful collaboration: A journey of more than 30 years with George Yin

Abstract

This article highlights my lifelong friendship and collaboration with George Yin on developing new methodologies in diversified fields in control theory and their branches, as well as their engineering and medical applications. It explains the roots and motivations in initiating these problems and George's critical contributions in applying his extensive expertise in stochastic systems to bring these challenging pursuits to fruitful new frameworks and methodologies.George and I have collaborated for more than 30 years on problems in the intersection of applied mathematics and engineering. The themes of our joint work have always been motivated strongly by engineering systems, evolving with emerging technologies. They are mostly focused on theoretical aspects in control systems and their branches, aiming for new frameworks and methodologies that deal with different types of uncertainties, information, and complexity.George started his work at Wayne State University (WSU) in 1987 in the Mathematics Department, three years prior to my faculty position in the Department of Electrical Engineering of WSU in 1990. While I knew George around my PhD graduation via friends, conferences, and occasional interactions, our actual joint work started in the mid 1990s, and then it quickly became much more intensive and comprehensive. 1. Backgrounds. Our collaboration has the roots in many aspects of my lifelong pursuit of dealing with uncertainties, information, and complexity, both in theory and in applications. Some themes were initiated well before my PhD graduation, and others were due to my personal interests, and still others stemmed from the unique locations of WSU as well as my personal connections. These may be summarized in the following three background categories.1. Integration of Deterministic and Stochastic Frameworks. During the final years of my PhD program at McGill University, my supervisor, George Zames, started to think about possibility of employing both deterministic and stochastic frameworks to treat uncertainties. In the late 1980s, many people in the field of H ∞ control tried to extend the H ∞ robust control theory to the