[R] Does inverse function exist

[phwang2000 at ucla.edu]

Hi,

I wrote a simple derivative program

(ftest=deriv(y~x^2, c("x"), function(x){} ))

I put (ftest=deriv(y~x^2, c("x"), function(x){} ))(1) which return 2  
which is correct.

however, if I want the output to be 0 and hopefully a new inverse  
function can take in output (2) and return x=1. Can this be  
accomplished. Maybe output(0) can return x=0

Thanks
pat