Optimality and sub-optimality of iterative identification and control design schemes

We demonstrate that some recently proposed iterative identification and control design schemes do not necessarily converge to a local minimum of the design objective in the case of a restricted complexity model. There is, however, a link between these approaches and a recently proposed iterative optimization based control design procedure based on experimental data. We show that if the achieved and the desired output responses are perfectly matched, the schemes are (essentially) equivalent under noise free conditions.