[R] Problem specifying Gamma distribution in lme4/glmer

[Matthew Giovanni]

Dear R and lme4 users-

I am trying to fit a mixed-effects model, with the glmer function in
lme4, to right-skewed, zero-inflated, non-normal data representing
understory grass and forb biomass (continuous) as a function of tree
density (indicated by leaf-area).  Thus, I have tried to specify a
Gamma distribution with a log-link function but consistently receive
an error as follows:

> total=glmer(total~gla4+(1|plot)+(1|year/month),data=veg,family=Gamma(link=log))
> summary(total)
Error in asMethod(object) : matrix is not symmetric [1,2]

I have also tried fitting glmm's with lme4 and glmer to other
Gamma-distributed data but receive the same error.  Has anyone had
similar problems and found any solutions?

Thank you for your input.  Best regards,
___________________________________
Matt Giovanni, Ph.D.
NSERC Visiting Research Fellow
Canadian Wildlife Service
2365 Albert St., Room 300
Regina, SK S4P 4K1
306-780-6121 work
402-617-3764 mobile
http://sites.google.com/site/matthewgiovanni/