Thanks for your help !
I got another problem with my function :
test <- function(x,bb0=-3,bb1=5,c0=2,r0=0) {
  ((exp(c0-r0)*(bb0+x)*(bb1-x))/((bb0+x+1)*(bb1-x-1))-1)}

With this :
curve(test(x),from=-10,to=10)

we can see that there are 2 roots : one in [3,4] and one in [5,10]
> uniroot(test,c(5, 10))$root
[1] 5.243265
> uniroot(test,c(3, 4))$root
[1] 3.069772

Even this works :
> uniroot(test,c(3, 10))$root
[1] 5.243263

but it's unfortunate that :
> uniroot(test3,c(-10, 10))$root
*Erreur dans uniroot(test3, c(-10, 10)) :
  les valeurs de f() aux points extrêmes ne sont pas de signe opposé*
doesn't work, because I have to find the root for c0 in [-10,10] but I can't
change the range at each loop:

I want to do something like this, do you have any ideas ?

> for (i in -10:10) {
+ z <- uniroot(test,c(-10, 10), c0=i)$root
+ print(z)}

Yann

On Wed, Jun 10, 2009 at 2:33 AM, Ben Bolker <bolker@ufl.edu> wrote:

>
>
>
> Peter Alspach wrote:
> >
> > Tena koe Yann
> >
> > It may not be the only problem, but you are missing an operator between
> > (bb0+x+1) and (bb1-x-1).
> >
> >
>
> And fixing that typo and viewing the function shows that it
> is a bit problematic on this interval anyway ...  (diverges
> at x = 1, closer look shows it's pretty nasty -- I haven't stopped
> to think about its behavior very carefully, but it will clearly
> take some effort.  If you're lucky there is a typo and the
> real function is better behaved!)
>
> test <- function(x,bb0=-3,bb1=5,c0=2,r0=0) {
>   ((exp(c0-r0)*(bb0+x)*(bb1-x))/((bb0+x+1)*(bb1-x-1))-1)}
>
>
> uniroot(test,c(-100,100))$root
> curve(test(x),from=-100,to=100)
> curve(test(x),from=1.00001,to=10)
> abline(h=0,col=2)
> --
> View this message in context:
> http://www.nabble.com/Problem-%3A-solving-a-equation-with-R-%2C-fail-with-uniroot-function-tp23953174p23953614.html
> Sent from the R help mailing list archive at Nabble.com.
>
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>

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