Question about GLMER

I am cc:ing the R-SIG-Mixed-Models at R-project.org mailing list on this
reply as such questions are often answered more quickly on that list.

Dear R Help,

I believe the glmer() function in lme4 automatically fits an
unstrucruted covariance matirx for the random effects.
Is that true?

The short answer is "no".

The longer answer is that you will need to be more specific about the
form of the data and the model before your question can be answered.
"unstructured" variance-covariance is SAS-speak (and an oxymoron, but
I promise not to rant about that).

So please give us a context.

? ?If so, do I have an option to somehow ask for a
diagonal structured covariance matrix?