How much do we need to experiment in order to adapt?

Adaptive control is about constructing controllers formed by two parts, where the first part (estimation unit) is aimed at estimating relevant plant characteristics, and the second part (control unit) exercises the control action by exploiting the outcomes of the estimation part. Adaptation, i.e. control unit tuning, can take place continuously during the normal operation of the system (on-line adaptation), or it can be performed every now and then. The limit case when information is first accrued and used to tune the control unit, which is otherwise kept fixed afterward, is called off-line adaptation.