“…To further improve the identification accuracy, in the follow-up studies, some other regularization methods [ 18 ], such as the function expansion method [ 20 , 21 , 22 ], multiplicative regularization [ 23 , 24 ], sparse regularization [ 25 , 26 , 27 , 28 ], and so on [ 29 , 30 , 31 , 32 ], are introduced into the force identification problem. In particular, for the time-varying external force, it is usually not sparse in the time domain.…”