[R] Finding Zeros of a Function

[Lorenzo Isella]

Hello,
And sorry for the late reply.
You see, my problem is that it is not known a priori whether I have one 
or two zeros of my function in the interval where I am considering it; 
on top of that, does BBsolve allow me to select an interval of variation 
of x?
Many thanks

Lorenzo



On 09/26/2010 04:31 AM, Jorge Ivan Velez wrote:
> Dear Lorenzo,
>
> You could try the BB package:
>
> # function we need the roots for
>
> fn1 <- function(x, a) - x^2 + x + a
>
>
> # plot
>
> curve(fn1(x, a = 5), -4, 4)
>
> abline(h=0, col = 2)
>
>
> # searching the roots in (-4, 4)
>
> # install.packages('BB')
>
> require(BB)
>
> BBsolve(par = c(-1, 1), fn = fn1, a = 5)
>
> values <- BBsolve(par = c(-1, 1), fn = fn1, a = 5)$par
>
> values
>
>
> # adding the roots to the plot
>
> points(values, c(0, 0), pch = 8, cex = 1.1, col = 4)
>
>
> HTH,
> Jorge
>
>
> On Sat, Sep 25, 2010 at 8:24 PM, Lorenzo Isella <> wrote:
>
>     Dear All,
>     I need to find the (possible multiple) zeros of a function f within
>     an interval. I gave uniroot a try, but it just returns one zero and
>     I need to provide it with an interval [a,b] such that f(a)f(b)<0.
>     Is there any function to find the multiple zeros of f in (a,b)
>     without constraints on the sign of f(a) and f(b)?
>     Many thanks
>
>     Lorenzo
>
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