Try `poly(Time, 2, raw=TRUE)' Here is an example:
Time <- runif(100) demand <- 1 + 0.5 * Time - 1.2 * Time^2 + rt(100, df=4) rq1 <- rq(demand ~ Time + I(Time^2), tau = 1:3/4) rq2 <- rq(demand ~ poly(Time, 2, raw=TRUE), tau = 1:3/4) all.equal(c(rq1$coef), c(rq2$coef)) Ravi. ---------------------------------------------------------------------------- ------- Ravi Varadhan, Ph.D. Assistant Professor, The Center on Aging and Health Division of Geriatric Medicine and Gerontology Johns Hopkins University Ph: (410) 502-2619 Fax: (410) 614-9625 Email: rvarad...@jhmi.edu Webpage: http://www.jhsph.edu/agingandhealth/People/Faculty_personal_pages/Varadhan.h tml ---------------------------------------------------------------------------- -------- -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of despaired Sent: Tuesday, June 09, 2009 11:59 AM To: r-help@r-project.org Subject: Re: [R] Non-linear regression/Quantile regression Hi, thanks, it works :-) But where is the difference between demand ~ Time + I(Time^2) and demand ~ poly(Time, 2) ? Or: How do I have to interpret the results? (I get different results for the two methods) Thank you again! Gabor Grothendieck wrote: > > Those are linear in the coefficients so try these: > > library(quantreg) > > rq1 <- rq(demand ~ Time + I(Time^2), data = BOD, tau= 1:3/4); rq1 > > # or > rq2 <- rq(demand ~ poly(Time, 2), data = BOD, tau = 1:3/4); rq2 > > > On Tue, Jun 9, 2009 at 10:55 AM, despaired<meyfa...@uni-potsdam.de> wrote: >> >> Hi, >> >> I'm relatively new to R and need to do a quantile regression. Linear >> quantile regression works, but for my data I need some quadratic >> function. >> So I guess, I have to use a nonlinear quantile regression. I tried >> the example on the help page for nlrq with my data and it worked. But >> the example there was with a SSlogis model. Trying to write >> >> dat.nlrq <- nlrq(BM ~ I(Regen100^2), data=dat, tau=0.25, trace=TRUE) >> >> or >> >> dat.nlrq <- nlrq(BM ~ poly(Regen100^2), data=dat, tau=0.25, >> trace=TRUE) >> >> (I don't know the difference) both gave me the following error message: >> >> error in getInitial.default(func, data, mCall = >> as.list(match.call(func, >> : >> no 'getInitial' method found for "function" objects >> >> Looking in getInitial, it must have to do something with the starting >> parameters or selfStart model. But I have no idea, what this is and >> how I handle this problem. Can anyone please help? >> >> Thanks a lot in advance! >> -- >> View this message in context: >> http://www.nabble.com/Non-linear-regression-Quantile-regression-tp239 >> 44530p23944530.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. >> > > ______________________________________________ > 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. > > -- View this message in context: http://www.nabble.com/Non-linear-regression-Quantile-regression-tp23944530p2 3945900.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. ______________________________________________ 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.
