Dear R-users,
I'm new to R, so my apologies if this question doesn't make sense.
I've tried the following model in lmer, and it works perfectly:
model<-lmer(aphids~densroot+zone+(1|zone/site), family=quasipoisson)
But if I try the exact same model with a different variable, totmas, the model
looks as follows:
model<-lmer(aphids~totmas+zone+(1|zone/site), family=quasipoisson)
Totmas is also a continuous variable just like densroot, but in this case I
receive the following message:
CHOLMOD warning: &Ãâ e
Error in objective(.par, ...) :
Cholmod error `matrix not positive definite' at
file:../Supernodal/t_cholmod_super_numeric.c, line 613
Moreover, if I test yet another continuous variable "vitality", to my surprise
R just crashes completely.
This is a mystery to me, especially because the variables totmas or vitality
don't give any problem when I build the exact same models in SAS with proc
glimmix...
Does someone have experience with this type of problem?
Thank you in advance,
Martijn.
--
Martijn Vandegehuchte
Ghent University
Department Biology
Terrestrial Ecology Unit
K.L.Ledeganckstraat 35
B-9000 Ghent
telephone: +32 (0)9/264 50 84
e-mail: [EMAIL PROTECTED]
website TEREC: www.ecology.ugent.be/terec
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