Somewhat surprisingly, the ideas of Morari et al. (1980) received very little attention.
One reason is probably that the paper also dealt with the issue of finding the optimal operation (and not only on how to implement it), and another reason is that the only example
in the paper happened to result in an implementation with the controlled variables at their
constraints. The constrained case is “easy” from an implementation point of view, because
the simplest and optimal implementation is to simply maintain the constrained variables at
their constraints. No example was given for the more difficult unconstrained case, where the
choice of controlled (feedback) variables is a critical issue. The follow-up paper by Arkun
and Stephanopoulos (1980) concentrated further on the constrained case and tracking of active constraints.