[R] Non-linear Least Square Optimization -- Function of two variables.

[Lorenzo Isella]

Dear All,
In the past I have often used minpack (http://bit.ly/zXVls3) relying
on the Levenberg-Marquardt algorithm to perform non-linear fittings.
However, I have always dealt with a function of a single variable.
Is there any difference if the function depends on two variables?
To fix the ideas, please consider the function

f(R,N)=(a/(log(2*N))+b)*R+c*N^d,

where a,b,c,d are fit parameters.
For a set of values {N_i, R_i}, i=1,2,.....etc... can I use minpack as
for the case of function of a single variable?
Should I instead resort to another package?
Any suggestion is welcome.
Many thanks

Lorenzo