Hi, if I have posted this twice, please ignore this. I'm not sure if I sent it to the correct e-mail address the first time.
I have a data set on germination and plant growth with the following variables: dataset=fm mass (response) sub (fixed effect) moist (fixed effect) pop (fixed effect) mum (random effect nested within population) iheight (covariate) plot (random effect- whole plot factor for split-plot design). I want to see if moist or sub interacts with mum for any of the pops, but I am getting an error message. This is the formula I used: fm$pmu <- getGroups(fm, ~1|pop/mum, level=2) fm$grp = as.factor(rep(1,nrow(fm))) fm$pl <- getGroups(fm, ~1|plot) fm$mo <- getGroups(fm, ~1|moist) fm$su <- getGroups(fm, ~1|sub) > fm1 <- lme(sqrt(mass) ~ iheight + moist*sub*pop, data=fm, random=list(grp=pdBlocked(list(pdIdent(~pl - 1), pdIdent(~pmu - 1), pdIdent(~pmu:su - 1), pdIdent(~pmu:mo - 1))))) Error in chol((value + t(value))/2) : non-positive definite matrix in chol I know the problem is with the random interaction terms, but I don't know how to overcome this. Any advice would be greatly appreciated. I'm new to R and analysis such as this. Thank you, Sarah Mclean [EMAIL PROTECTED] http://mobile.yahoo.com.au - Yahoo! Mobile - Check & compose your email via SMS on your Telstra or Vodafone mobile. ______________________________________________ [EMAIL PROTECTED] mailing list https://www.stat.math.ethz.ch/mailman/listinfo/r-help