[R-sig-ME] Convergence issues with nlme:lme

[Robert Long]

Dear list

Having tried to fit a mixed effects model with nlme:lme, and found
convergence problems, how do we inspect the fitted model object to find out
what is the problem?

Reproducible example:

> set.seed(3)
> data <- data.frame(y = rnorm(100), x = rnorm(100), group = rep(1:10, each
= 10))
>
> model <- lme(y ~ x, random = ~ 1 + x | group, data = data)
Error in lme.formula(y ~ x, random = ~1 + x | group, data = data) :
  nlminb problem, convergence error code = 1
  message = iteration limit reached without convergence (10)

Now that we have the model object, how do we interrogate it to find out
what went wrong? I need to do this in code, so I won't have access to the
Error message raised when the model was first fitted (unless there is a
magical way to get at the error (which I haven't yet found)

Thanks !

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