* Summary *

Input-to-state stability is an L infinity stability property for systems with disturbances that was introduced by Sontag in 1989. Roughly
speaking a system is ISS if bounded inputs imply that the states are bounded and, moreover, the ultimate bound on trajectories depends only on
the disturbance size. This
property turned out to be very useful and natural to use in many context and has helped generate numerous new analysis and design
methods for nonlinear systems. There are many equivalent characterizations of ISS each of which may be important in certain situations.
In particular, its Lyapunov characterization makes a nice link to Lyapunov theory and provides a tool to check ISS via the so called
Lyapunov ISS functions. Another notion that is very important in this context is the nonlinear gain function that allows one to
state small gain theorems that are very useful in robustness analysis, as well as nonlinear controller design.
Many other variants of the ISS property are available, including the integral ISS (iISS), input-output-to-state stability (IOSS), and so on.

A large majority of my work uses the ISS methodology in different contexts, such as sampled-data nonlinear systems or averaging.
However, there several results in which I was exclusively dealing with analysis of the ISS gains or design of input-to-state stabilizing
controllers. In particular, we have presented a framework for computation of "smallest" ISS gains via the technique of dynamic programming.
Moreover, we provided a unifying framework for design of controllers to
achieve various ISS like properties using the method of dynamic programming. I also developed a controller for a class of nonlinear systems with
positive outputs that achieve ISS with respect to measurement disturbances, which is known to be a hard problem for general nonlinear systems.

* Collaborators *

Prof. E.D. Sontag
Prof. M.R.James
Dr. S. Huang
Dr. P.M. Dower
* Selected publications *

D. Angeli and D. Nesic, "Power characterizations of input-to-state stability and integral input-to-state stability", IEEE Trans. Automat. Contr, vol.46, No. 8 (2001), pp. 1298-1303.
D. Nesic and E. D. Sontag, "Input-to-state stability of linear systems with positive measurements", Sys. Contr. Lett., vol. 35 (1998), pp. 245-255.
S. Huang, M.R. James, D. Nesic and P.M. Dower, "Analysis of input to state stability for discrete-time nonlinear systems via dynamic programming" , to appear in Automatica, 2005.
S. Huang, M. James, D. Nesic and P. M. Dower, "Measurement feedback controller design to achieve input to state stability" , in Proc. 43rd Conf. Decis. Contr., Bahamas, pp. 2613-2618, 2004. (expanded version to appear in IEEE Trans. Automat. Contr.)