[R] error message from gls(), unstructured in lower triangle, identical diagonal, help.

P L l12345p2000 at yahoo.com
Sun Mar 2 23:35:04 CET 2003

> It's just by chance that this happened: the
> correlation you generated 
> was not strong enough, or was far from an
> unstructured correlation and 
> the algorithm did not converge (and you obtained
> this error message).
> Generate another sample might solve the problem.

I think that you help me on the right point. Since
nlme() uses EM and Newton-Raphson in sequence, other
than that PROC MIXED uses Newton-Raphson only, as I
know, I am wondering whether PROC MIXED can circumvent
this situation. But the problem is as what I mentioned
in the first mail, which is I do not know how to
structure the var-cor with unstructured lower triangle
and identical diagonal in PROC MIXED.

> You might try "for fun" but it does not make much
> sense to me.

I am now doing a project which needs to generate
random samples, and fit them using mixed models with
different var-cov structures. If the problem that I
met is common, then I need to revise my codes a little

Thank you for breaking my problem.

Peng Liu                      |
Division of Statistics        |
Northern Illinois University  |
De Kalb, IL 60115, USA        |
E-mail: pliu at math.niu.edu     |

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