I've tried lm, but something is wrong. I've made a test dataset of 599 data points, my original equation is
zz = 1 +0.5*xx -3.2*xx*xx -1*yy +4.2*yy*yy but the R gives this result: ------------------------------------------------------- > mp <- read.csv(file="sample.csv",sep=";",header=TRUE) > lm(zz ~ poly(xx,2) + poly(yy,2), data=mp) Call: lm(formula = zz ~ poly(xx, 2) + poly(yy, 2), data = mp) Coefficients: (Intercept) poly(xx, 2)1 poly(xx, 2)2 poly(yy, 2)1 poly(yy, 2)2 25.86 -2239.86 -595.01 2875.54 776.84 ----------------------------------------------------------- which is definitely not the original. :( (In case of interest the test dataset is available here: szisziszilvi.lima-city.de/r) -- View this message in context: http://r.789695.n4.nabble.com/non-linear-regression-for-3D-data-tp2320982p2322779.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.