The classical control theory shows performance limitations
when applied to highly complex processes, where
non-linearity and complex dynamic behaviors are present.
However in the industrial environment, complex processes
are controlled by operators, based exclusively on imprecise
information and specialized knowledge of the processes.
Conventional controllers deal with the non-linearity
of physical systems by approximations, trying to map
the processes with input and output variables. The best
procedure is chosen based on costs, complexity and performance
implementation (Abreu & Ribeiro, 1999).