I want to learn to use houdnin with more physics and maths knowledge,
and I hear of there are some document with houdini v4.0,but I cant find the files , can anybody help me? thanks

There's this one [b.fx.free.fr] from 5.5 floating around out there, but I'm not sure if anyone has older.

There's also the HScript expressions video tutorials on in the Tutorials section on this site.

Allegro: thank you very much, I found your file,this file is very useful to me,I am learn expression and hscript of houdini,thanks for your help ,If you have some more help file ,please give me the links ,thanks