getting variable length numerical gradient

Hi all.
I have a numerical function f(x), with x being a vector of generic
size (say k=4), and I wanna take the numerically computed gradient,
using deriv or numericDeriv (or something else).

My difficulties here are that in deriv and numericDeric the function
is passed as an expression, and one have to pass the list of variables
involved as a char vector... So, it's a pure R programming question.


Have a nice sunday,
Antonio, Fabio Di Narzo.