[R] Numerical Derivatives in R

[Tolga Uzuner]

Hi,

Suppose I have an arbitrary function:

arbfun<-function(x) {...}

Is there a robust implementation of a numerical derivative routine in R 
which I can use to take it's derivative ? Something a bit more than 
simple division by delta of the difference of evaluating the function at 
x and x+delta...

Perhaps there is a way to do this using D or deriv but I could not 
figure it out. Trying:

eval(deriv(function(x) arbfun(x),"x"),1)

does not seem to work.

Thanks,
Tolga