Tracking controlled states over a large range of accessible parameters
is a process which allows for the experimental continuation of unstab
le states in both chaotic and non-chaotic parameter regions of interes
t. In algorithmic form, tracking allows experimentalists to examine ma
ny of the unstable states responsible for much of the observed nonline
ar dynamic phenomena. Here: we present a theoretical foundation for tr
acking cent-roiled states from both dynamical systems as well as contr
ol theoretic viewpoints. The theory is constructive and shows explicit
ly how to track a curve of unstable states as a parameter is changed.
Applications of the theory to various forms Of control currently used
in dynamical system experiments are discussed. Examples from both nume
rical and physical experiments are given to illustrate the wide range
of tracking applications. (C) 1997 American Institute of Physics.