search for: bodymass

Hi all I try to make a weibull survival analysis on R. I know make this on GLIM, and now I try to make the GLIM exercice GLEX8 on R to learning and compare the test. The variables are: time censor group bodymass In GLIM I make: $calc %s=1 $ to fit weibull rather than exponential $input %pcl weibull $ $macro model group*bodymass $endmac$ $use weibull t w %s $ Then, GLIM estimate an alpha for the model group*bodymass, the value on GLIM is 0.736. I try to make this on R. > survreg(Surv(time,censor)~gr...

...ing value or an Infinity produced when evaluating >the model >Date: Wed, 23 Apr 2003 15:22:37 +0200 > >Hi Angel, > >I tried reparametrise your model, setting: > >BirthMass^0.25=u >MaxMass^0.25=v > >and giving the following formula in R: > >GrowthModel<-nls(BodyMass~(((1-(1-u/v)*exp(-a*Time/(4*v)))^4)*v^4),data=grow >th,start=c(u=4,v=5,a=1.5),trace=TRUE) > >And this works for me, but the u estimate is negative (not significantly >different from 0, though). > >Christian > >----- Original Message ----- >From: "Angel -" <an...

...i, I am trying to fit a sigmoid curve to some data with nls but I am getting into some trouble. Seems that the optimization method is getting down to some parameter estimates that make the equation unsolvable. This is an example: >growth<-data.frame(Time=c(5,7,9,11,13,15,17,19,21,23,25,27),BodyMass=c(45,85,125,210,300,485,570,700,830,940,1030,1120)) >GrowthModel<-nls(BodyMass~(((1-(1-((BirthMass/MaxMass)^0.25))*exp(-a*Time/(4*MaxMass^0.25)))^4)*MaxMass),data=growth,start=c(BirthMass=3,MaxMass=2500,a=1.5),trace=TRUE) 56043.86 : 3.0 2500.0 1.5 Error in numericDeriv(form[[3]], nam...