“…More recently, however, there has been intense interest in controlling problems whose models have significantly higher complexity, necessitating discretizations of much higher order. Such problems include semiconductor manufacturing reactors (e.g., Badgewell et al, 1994;Aling et al, 1997), reverse-flow and circulating-loop reactors (e.g., Nieken et al, 1994;Hua et al, 1998), control of transitional hydrodynamic flows (Joshi et al, 1997;Carlson and Lumley, 1997), or instabilities in turbines (Badmus et al, 1996;Paduano et al, 1994). Problems with complicated geometries and/or sharp variations of solutions or system parameters make the use of larger discretization models unavoidable (Aling et al, 1996;Aling et al, 1997;Bangia et al, 1997;Graham et al, 1993;Chakravarti et al, 1995).…”