Skip to Main Content
A technique for selecting a low-order system to approximate a high-order model has been suggested by Davison . A critical component in this technique is the criterion used to select the most appropriate order and modes for the low-order approximation. Criteria have been discussed and analyzed by Mahapatra , , Rao, Lamba, and Rao , and Elrazaz and Sinha . In this note we overcome deficiencies in the criteria that have been proposed and we introduce a new criterion which is rigorously justified. The criterion we suggest is also applicable when eigenvalues of the system are nonreal.