Add element-wise multiplication in formulas (#15834)
Summary:
Absence of element-wise multiplication can confused some beginners
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15834
Differential Revision: D13603369
Pulled By: soumith
fbshipit-source-id: 1d5c17c57778ddbb4b201122d826d1d6437204d1
