n order to evade the singularity problems, the
authors suggest a cascade approach, in which some of
the inputs are initially omitted from the model, resulting
in a MIMO system. After a controller is derived for
the MIMO system, the partial loop is closed, forming a
new process model, which is then used to determine the
proper controllers for the remaining inputs, by adding
them into the loop one by one and closing it after each
addition. In essence, for a two input, one output system
this implies