How can I write partial differential equations at S-function

Hello All I have a set of partial differential equations for a dynamic model of a reactor that I have decided to solve them by finite differences method. Now I have written code at M-file,run them and gives me well response.But my master professor force me to run the dynamic model at simulink.I think the only solution is writting the M-file code of finite differences method of solving PDE at S-function Simulink,But I don`t know how to write PDE at S-functin.If any body knows any solutions or has any examples of this subject,Please help me. thank you