Yan Wong <h.y.wong <at> leeds.ac.uk> writes: > > Although the 'spatial' documentation doesn't mention that extractAIC > works, it does seem to give an output.
Could I suggest moving this question to the R-sig-geo list? Please note that surf.ls() converts x and y to the [-1, +1] range to ensure that higher powers of possibly very large absolute coordinate values do not cause trouble, so that the surf.ls() and lm() models may differ anyway. I believe that there is a bug in extractAIC.trls() - which I contributed to the spatial package some years ago, with edf <- df.residual.trls(fit) rather than n - df.residual.trls(fit). When this is corrected, for this case, the extractAIC() results agree. Roger Bivand > I may have misunderstood, but shouldn't the following give at least > the same d.f.? > > > library(spatial) > > data(topo, package="MASS") > > extractAIC(surf.ls(2, topo)) > [1] 46.0000 437.5059 > > extractAIC(lm(z ~ x+I(x^2)+y+I(y^2)+x:y, topo)) > [1] 6.0000 357.5059 > > # and if the AIC values differ, shouldn't they do so by an additive > constant? > > > (extractAIC(surf.ls(2, topo))-extractAIC(lm(z ~ x+I(x^2)+y+I(y^2) > +x:y, topo)))[2] > [1] 80 > > (extractAIC(surf.ls(1, topo))-extractAIC(lm(z ~ x+y, topo)))[2] > [1] 92 > > # Using R 2.3.1 (OS X), spatial version 7.2-27.1 > > Thanks > > Yan > > ______________________________________________ > R-help <at> stat.math.ethz.ch 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. > > ______________________________________________ [email protected] 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.
