References for grdfft

I want to use grdfft. I have no problems to use it but I am not sure if I using it rigth. What could I read (books, articles) in order to understand the theory behind the differents tools available in grdfft (and to know how to used them properly)? Maybe the references could be add to the manpage. Thanks in advance.

Good idea, @Esteban82, we shall try to find some good references here.