Hi, Here is another approach:
set.seed(123) x <- sort(runif(200)) y <- sin(3*pi*x) + rnorm(200, sd=0.1) smspl <- smooth.spline(x, y) d2 <- function(x) predict(smspl, x , deriv=2)$y x <- seq(0, 1, length=500) plot(x, d2(x), type="l") abline(h=0, lty=2) uniroot(f=d2, interval=c(0.1, 0.5)) # first inflection point uniroot(f=d2, interval=c(0.5, 0.9)) # second inflection point Ravi. ____________________________________________________________________ Ravi Varadhan, Ph.D. Assistant Professor, Division of Geriatric Medicine and Gerontology School of Medicine Johns Hopkins University Ph. (410) 502-2619 email: rvarad...@jhmi.edu ----- Original Message ----- From: David Winsemius <dwinsem...@comcast.net> Date: Saturday, March 28, 2009 5:58 pm Subject: Re: [R] Find inflection points using smooth.spline To: r-h...@stat.math.ethz.ch > T.D.Rudolph <prairie.picker <at> gmail.com> writes: > > > > > > > Is there any way to identify or infer the inflection points in a smooth > > spline object? I am doing a comparison of various methods of time-series > > analysis (polynomial regression, spline smoothing, recursive partitioning) > > and I am specifically interested in obtaining the julian dates associated > > with the inflection points inferred by the various models. > > > > Tyler > > > > e.g. > > smooth.spline.pdf > > > You can get an analog of first and second derivatives via using first > and > second differences: > > ?diff > > If your spline object is spl, try: > > diff(diff(spl)) > > It's possible that you would find lag and rle functions useful as well. > > -- > David Winsemius > > ______________________________________________ > R-help@r-project.org mailing list > > PLEASE do read the posting guide > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ 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.
