Before revision:  The nonlinearities in the ROM are efficiently computed by discrete empirical interpolation method (DEIM) . Preservation of the energy (Hamiltonian), and other conserved quantities ;
After revision:  The nonlinearities in the ROM are efficiently computed by discrete empirical interpolation method (DEIM) method to reduce the computational cost. The computation of the reduced-order solutions is accelerated further by the use of tensor techniques. The overall procedure yields a clear separation of the offline and online computational cost of the reduced solutions. The accuracy and computational efficiency of the ROMs are demonstrated for a numerical test problem. Preservation of the energy (Hamiltonian), and other conserved quantities ;