1. A computer-implemented method for estimating a time-varying parameter of a simulated nonlinear system, comprising: (a) receiving by a computer input data for the simulated nonlinear system, the input data comprising a desired state and a desired state derivative of the simulated nonlinear system at a plurality of time points; (b) generating by the computer for one of the plurality of time points an approximate time-varying parameter based on at least the desired state, the desired state derivative, a simulated approximate state of the simulated nonlinear system, and a Lyapunov function; (c) providing by the computer the approximate time-varying parameter for the one of the plurality of time points; and (d) determining by the computer, an approximate state for a next time point and an approximate state derivative for a current time point of the simulated nonlinear system using the approximate time-varying parameter, wherein the computer is programmed to execute steps (a)-(d).