[R] Does inverse function exist

[Prof Brian Ripley]

Inverting a linear function is easy, and more generally functions need not 
be invertible.  But uniroot() is very helpful in finding an inverse of a 
monotonic function, and the idea is used in some of the qxxxxx functions.

On Fri, 26 Jan 2007, phwang2000 at ucla.edu wrote:

> 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
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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