# [R] Inverse function

Bert Gunter gunter.berton at gene.com
Wed Feb 24 22:14:19 CET 2010

```1. Is this a homework problem?

2. Etiquette on this list is to sign with your full real name. Adhering to
the list etiquette may enhance your chance of a useful response, especially
in view of (1), as we (or at least some of us) do not wish to do students'
homework for them.

3. Hint: f(y,r) = a  <==>  g(y) = 0 where g(y) == f(y,r) - a
(for numerical solutions).

Bert Gunter
Genentech Nonclinical Biostatistics

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of li li
Sent: Wednesday, February 24, 2010 12:46 PM
To: r-help
Subject: [R] Inverse function

Hi all,
I have a function like the following:

f <- function(r,
y){r/(2*pi)*exp(1)^(-y)*(1+r*(y/2)+r^(2)*(y-1)^(2)/6)}

For fixed r, I want to find the inverse funtion in terms y.
In other words, for fixed r, if the value of the function is given, I want
to
find the corrsponding y value that will achieve the specific function value.

Can anyone help me?
Hannah

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