Now that I have accomplished learning and applying various linear system identification techniques to simulated data sets.
I am looking now to dig deeper into the world of system identification by learning nonlinear system ID.
I've encountered in many literatures involving models with nonlinear sys ID that they tend to be superior over all linear system ID techniques. This could be justified by the scarcity of linear regions in many dataset where linear system ID would work.
Therefore, I would kindly ask for your help regarding what references are useful to learn about nonlinear system identification. I have read Ljung's famous book completely and I have aquired all the knowledge needed to apply linear system ID models and how to validate them.