[R] Looking for package to solve for exponent using newton's method

[Duncan Murdoch]

On 10/10/2013 2:39 PM, Ken Takagi wrote:
> Hi,
> I'm looking for an R function/package that will let me solve problems of the
> type:
>
> 13 = 2^x + 3^x.
>
> The answer to this example is x = 2, but I'm looking for solutions when x
> isn't so easily determined. Looking around, it seems that there is no
> algebraic solution for x, unless I'm mistaken.  Does anyone know a good
> package to solve these types of problems? Are there built in functions to do
> this?

You can get approximate solutions using uniroot:

 > uniroot(function(x) 2^x + 3^x - 13, c(0, 10))
$root
[1] 1.99998

$f.root
[1] -0.0002581592

$iter
[1] 10

$estim.prec
[1] 6.103516e-05