6. Highlighting the platitude

One of the tricky aspects of flatness control lies in the identification of the flatness property and the proposal of a flat output. Although in most practical cases the flat output is physically interpretable, there are cases where it is not obvious to have intuition for a candidate flat output. For systems described by nonlinear differential equations, we'll look at some of the criteria that can be used to come to a conclusion on this point, and at procedures that can help guide the choice of a flat output.