I have conducted a THz experiment to measure the conductivity of CNTs. Now I have a set of experimental data using which I plotted conductivity vs. frequency graph. I need to compare it with various conductivity models. But in every model, for example- Drude Smith model, there are many non- linear parameters and I need to find out those values for the set of parameters for which the theoretical curve fits the one I got from the experimental data. Is there any method that I can use? Can anyone help me here?