1. A method of generating a nonlinear simulation model of a device under test (DUT), the method comprising: receiving large-signal nonlinear waveform data based on responses of the DUT to input signals; determining a set of first dynamical variables and a set of second dynamical variables from the nonlinear waveform data; calculating values of second dynamical variables; providing nonlinear constitutive relations as functions of the first dynamical variables and the calculated values of the second dynamical variables; and compiling the nonlinear simulation model of the DUT using the identified nonlinear constitutive relations.