1. There is direct feedback from y(t) to u(t) (like a P-regulator). In that case it is essential not to let this feedbac

[fyousefi]

1. There is direct feedback from y(t) to u(t) (like a P-regulator). In that case it is essential not to let this feedback influence the model. It is thus important always to use nk>0 for these inputs in state-space and input-output models.