I'm working on a project that involves a Joule thief. I need to model the magnetization process of the ferrite core of the toroid. With that I will be able to get an accurate picture of the flux change, which I can use to predict the induced emf based on the characteristics of the system. Everything I learned as an undergrad either involved linear media, or just the behavior of a material after magnetization has happened. I need to learn about the magnetization process in ferrous materials. Can anyone either explain the necessary math or point me in the direction of reading materials that will give me a mathematical overview of these processes? thank you very much.