[R] Inverse function

[Bert Gunter]

1. Is this a homework problem?

2. Etiquette on this list is to sign with your full real name. Adhering to
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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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