“…Popular linear projection techniques include the proper orthogonal decomposition (POD) [9], the reduced basis method [10], and the balanced truncation method [11], while autoencoders [12,13] are often applied for nonlinear projection [14,15,16]. The linear-subspace ROM (LS-ROM) has been successfully applied to various problems, such as nonlinear heat conduction [17], Lagrangian hydrodynamics [18,19,20], nonlinear diffusion equations [17,21], Burgers equations [20,22,23,24], convection-diffusion equations [25,26], Navier-Stokes equations [27,28], Boltzmann transport problems [29,30], fracture mechanics [31,32], molecular dynamics [33,34], fatigue analysis under cycling-induced plastic deformations [35], topology optimization [36,37], structural design optimization [38,39], etc. Despite successes of the classical LS-ROM in many applications, it is limited to the assumption that intrinsic solution space falls into a low-dimensional subspace, which means the solution space has a small Kolmogorov n-width.…”