set emacs imenu for m-file section

I hope to use imenu to manage section (%%) in m-file, but I don't know how to make it work. Anyone can show the related code in ~/.emacs for me about this function? Or, it's also useful for me if you know how to fold section, like the matlab editor did. It's really inconvenient to edit long m-file in emacs without imenu or code folding.