for closed-loop systems by a delay line method presented a new approach to the synthesis and analysis of closed-loop systems in the time domain. Ho collaborated with Rudolf E. Kálmán, a pioneer of modern control theory. Before Kálmán, time series analysis and classical control theory studied the frequency domain, using harmonic analysis, especially Laplace and Fourier transforms. Kálmán developed the study of the time domain using state-space models. Joining Kálmán, Ho showed that the state-space representation provides a convenient and compact way to model and analyze dynamical systems with multiple inputs and outputs which would otherwise take multiple Laplace transforms to encode; further, the state-space representation can be extended into nonlinear systems. Their paper controllability of linear dynamic systems, developed the theory of controllability (then known as the "Kalman-Bertram condition"). Together with Ho's student Robert Lee at MIT, the paper A Bayesian approach to problems in stochastic estimation and control formulated a general class of stochastic estimation and control problems from a Bayesian Decision-Theoretic viewpoint. Pattern recognition After joining the faculty of Harvard University, Ho developed the Ho-Kashyap rule in pattern recognition with his first Ph.D. student, Rangasami L. Kashyap. Game theory Turning his attention to game theory, Ho in 1965 published the paper Differential Games and Optimal Pursuit-Evasion Strategies, that proved the optimality of a proportional guidance scheme. His paper Nonzero Sum Differential Games was an influential game-theoretic study in systems and control, following earlier work by Samuel Karlin, for example. Discrete event dynamic systems Since the 1970s, Ho focused on research in discrete event dynamic systems, making contributions in perturbation analysis and ordinal optimization, including the book Perturbation Analysis of Discrete Event Dynamic Systems. and the book "Ordinal Optimization - Soft Optimization for Hard Problems" (Springer 2007) Publications Books About Yu-Chi Ho's work References External links Home Page at Harvard University Mathematics Genealogy Project profile Sciencenet.cn Blog Who's Who of Asian Americans biography Biography of Yu-Chi Ho from the Institute for Operations Research and the Management Sciences 1934 births Living people Scientists from Shanghai Control theorists Chinese emigrants to the United States Richard E. Bellman Control Heritage Award recipients Nanyang Model High School alumni Harvard University alumni John A. Paulson School of Engineering and Applied Sciences faculty MIT School of Engineering alumni Members of the United States National Academy of Engineering Foreign members of the Chinese Academy of Sciences Foreign members of the Chinese Academy of Engineering Fellows