Thomas Lumley <[EMAIL PROTECTED]> writes: > You might want to look at the function surface, eg: > > dd<-expand.grid(x=seq(0,2,length=20),y=seq(0,2,length=20)) > yy<-apply(dd,1,mfun1) > contour(seq(0,2,length=20),seq(0,2,length=20),matrix(yy,20),nlevels=40) > > The function is nearly flat on a fairly wide band where either x or y > is 1 or slightly larger, and so is far from quadratic in that region. > You need better starting values, or some rescaling of the objective > function.
A slight modification is quite revealing: dd<-expand.grid(x=seq(-1,2,length=100),y=seq(-1,2,length=100)) yy<-apply(dd,1,mfun1) persp(seq(-1,2,length=100),seq(-1,2,length=100),matrix(yy,100)^.1) contour(seq(-1,2,length=100),seq(-1,2,length=100),matrix(yy,100)^.1) abline(v=1.485,h=0) > Another optimisation algorithm might give different results, and in > fact if you try optim() you end up at (1,1) with method="Nelder-Mead" > and method="BFGS", but at (1.48,0) with "CG" or "L-BFGS-B". And SANN found (1,1) two times out of three for me, the third one getting stuck in the 3rd local minimum at (-0.72,1.22) -- O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907 ______________________________________________ [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
