This is a multiphysics model which couples electromagnetic field, thermal field and phase change field to get a fast simulation of the PCM phase changing process. It's model is a GST layer covering on the silicon waveguide.It needs matlab pdetoolbox to run,which gives its strong ability to simulated any kinds of custimized geometry,incident light,refractive index distribution etc. It's now incompleted and being tried on different degree of approximation to get both accuracy and efficiency. My final goal is to do reservoir computing with the PCM phase field. The idea came from the two articles: https://www.nature.com/articles/s41524-021-00655-w https://opg.optica.org/abstract.cfm?URI=optica-8-11-1388