Hi, I have a problem with fitting a nonlinear mixed-effects model to my data. I was able to fit quite simple exponential model but now I�m trying to fit the following Gompertz model:
> gomp<-nlme(paino~b0+b1*exp(-exp(-b2*(daydeg.scale-b3))), data=group1, fixed=b0+b1+b2+b3~1, start=c(b0=150, b1=3000, b2=0.6, b3=2500)) I�m getting the following error: Error in chol((value + t(value))/2) : the leading minor of order 2 is not positive definite Could you give me some ideas what might be wrong and how to deal with it? I know that the data and the syntax should be ok as I have tested it already with exponential model. The problem seems to be in the model-form. Many thanks, Niina Kotamaki University of Jyvaskyla ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help
