Nowadays, nonlinearity is involved in all walks of life. It is a challenge for
engineers to design controllers for all kinds of nonlinear systems. To handle this
issue, various nonlinear control theories have been developed, such as theories of
adaptive control, optimal control, and robust control. Among these theories, the
theory of optimal control has drawn considerable attention over the past several
decades. This is mainly because optimal control provides an effective way to design
controllers with guaranteed robustness properties as well as capabilities of opti-
mization and resource conservation that are important in manufacturing, vehicle
emission control, aerospace systems, power systems, chemical engineering pro-
cesses, and many other applications.
