  We are introducing a model-free control and a control with a restricted model
for finite-dimensional complex systems. This control design may be viewed as a
contribution to "intelligent" PID controllers, the tuning of which becomes
quite straightforward, even with highly nonlinear and/or time-varying systems.
Our main tool is a newly developed numerical differentiation. Differential
algebra provides the theoretical framework. Our approach is validated by
several numerical experiments.
