The coefficients are different but the predictions are the same. On Tue, Jun 9, 2009 at 12:41 PM, Greg Snow<greg.s...@imail.org> wrote: > poly by default uses orthogonal polynomials which work better mathematically > but are harder to interpret. See ?poly > > -- > Gregory (Greg) L. Snow Ph.D. > Statistical Data Center > Intermountain Healthcare > greg.s...@imail.org > 801.408.8111 > > >> -----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 9:59 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- >> tp23944530p23944530.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-tp23944530p23945900.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. >
______________________________________________ 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.
