Hi: Interesting. Try the following; f is copied and pasted directly from your e-mail:
f <- function(x) 2.5*exp(-0.5*(2*0.045 - x)) + 2.5*exp(-0.045) + 2.5*exp(-1.5*x) - 100 curve(f, -3, 8) # plot it in a localized region abline(0, 0, lty = 2) There are two places where the function crosses the x-axis, but not where you were expecting. The graph suggests one root between -3 and -2 and another between 7 and 8: Note that uniroot() takes an object of class function as its first argument and a search interval as its second. It is the R function that finds a zero of a univariate function. See ?uniroot for details. (And f is a function object; try class(f).) On Thu, Jul 29, 2010 at 1:32 AM, sammyny <sj...@caa.columbia.edu> wrote: > > Hi, > Is this method broken in R? I am using it to find roots of the following > function: > f(x) = 2.5*exp(-0.5*(2*0.045 - x)) + 2.5*exp(-0.045) + 2.5*exp(-1.5*x) - > 100 > Which method? It is never (conveniently) mentioned... Function? Package? > > It is giving an answer of -38.4762403 which is not even close (f(x) = > 2.903809e+25 for x=-38.4762403). The answer should be around 0.01-0.1. This > function should converge.. > > Even for a simple function like f(x) = exp(-x) * x, it gives answer as > 8.89210984 for which f(x) = 0.001222392 and I set tolerance to 10^-12.. > I see handwaving and fulminating, but no code... > > Also, is there a non graphical version of newton method? I looked at > nleqslv > but have no idea how to use it.. > > Thanks for your help. > HTH, Dennis > -- > View this message in context: > http://r.789695.n4.nabble.com/newton-method-tp2306111p2306111.html > Sent from the R help mailing list archive at Nabble.com. > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
