R help - Oct 2008 - Function question

Hi,

Let's say very simply there is a function:

f <- function (x) x^2

which is evaluated with :

f(2)

Now, I want to do the reverse so I want to now x for f(x) = 4

So, is there a way in R to solve x for some function f(x)=a?

I hope I explained it clear.

cheers,

Dennis

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try uniroot(), e.g.,

f <- function (x) x^2
uniroot(function(x, a) f(x) - a, c(0, 10), a = 4)


I hope it helps.

Best,
Dimitris


dennis11 wrote:
> Hi,
> 
> Let's say very simply there is a function:
> 
> f <- function (x) x^2
> 
> which is evaluated with :
> 
> f(2)
> 
> Now, I want to do the reverse so I want to now x for f(x) = 4
> 
> So, is there a way in R to solve x for some function f(x)=a?
> 
> I hope I explained it clear.
> 
> cheers,
> 
> Dennis
> 
-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus Medical Center

Address: PO Box 2040, 3000 CA Rotterdam, the Netherlands
Tel: +31/(0)10/7043478
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