Title: Optimal selection of controlled variables
Authors: Ivar J. Halvorsen, Sigurd Skogestad, John C. Morud, Vidar Alstad

Published in Ind.Eng.Chem.Res., 2003, Vol. 42, 3273-3284.

Abstract: This paper considers the selection of controlled variables
for the unconstrained  degrees of freedom, such that near-optimal
operation is achieved with constant setpoints (``self-optimizing control'').
From a second-order Taylor approximation around the optimal point, we derive 
an exact local method. This may be used to find
the optimal linear combination of measurements to use as controlled variables.
We also derive the approximate singular value rule, which 
is very useful for quick screening and elimination of poor 
candidate variables.