The engineering objective of high performance control using the tools of
optimal control theory, robust control theory, and adaptive control
theory is more achiev- able now than ever before, and the need has never
been greater. Of course, when we use the term high peiformance control
we are thinking of achieving this in the real world with all its
complexity, uncertainty and variability. Since we do not expect to
always achieve our desires, a more complete title for this book could be
"Towards High Performance Control". To illustrate our task, consider as
an example a disk drive tracking system for a portable computer. The
better the controller performance in the presence of eccen- tricity
uncertainties and external disturbances, such as vibrations when
operated in a moving vehicle, the more tracks can be used on the disk
and the more memory it has. Many systems today are control system
limited and the quest is for high performance in the real world.