And if you need some extra digits:
require(Rmpfr)
testfn<-function(x){2^x+3^x-13}
myint<-c(mpfr(-5,precBits=1000),mpfr(5,precBits=1000))
myroot<-unirootR(testfn, myint, tol=1e-30)
myrootJohn Nash On 13-10-11 06:00 AM, r-help-requ...@r-project.org wrote:
Message: 33 Date: Thu, 10 Oct 2013 21:03:00 +0200 From: Berend Hasselman<b...@xs4all.nl> To: Ken Takagi<katak...@bu.edu> Cc:r-h...@stat.math.ethz.ch Subject: Re: [R] Looking for package to solve for exponent using newton's method Message-ID:<a12b1f57-a38f-470d-a6d7-479f94125...@xs4all.nl> Content-Type: text/plain; charset="us-ascii" On 10-10-2013, at 20:39, Ken Takagi<katak...@bu.edu> 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? >Univariate equations can be solved with uniroot, available in base R. You can also use package nleqslv for this but that is intended for systems of nonlinear equations. It does however solve your equation. There is also BB which is especially intended for large sparse systems. Berend
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