[R-sig-ME] [R] lme4 : lmer : convergence problem and other errors

[yufeng at nsm.umass.edu]

Please see below:

> 1) What version of lmer are you running? The new version post 23/6/08 copes
> with difficult likelihoods better.

I used the most up-to-date version.

> 2) Have you changed anything in the elements of the control parameter. The
> pre 23/6 verion had several parameters and the later one fewer. In
> particular you can increase the iterations

How could I increase the iterations?

> 3) Have you centred your x variables so they have means around zero. If not
> you should always do this as it will make the fitting easier especially with
> quadratic terms. This ought to have been my first suggestion.

Do u mean the random effects of x's should be centered around 0? I didn't do
that and I don't know how to do that in R? Could U tell me how? Thanks!



> 4) Having another look at your model you say it is non-linear, but it looks
> linear to me if you set the squared terms as covariates too.

You are right the model should be linear.

>
> Good luck
>
> Gillian Raab
> Edinburgh
>
> On 03/07/2008, yufeng at nsm.umass.edu <yufeng at nsm.umass.edu> wrote:
> >
> > Dear R-user,
> >
> > I am trying to use the R "lmer" function in lme4 package to fit a non
> > linear
> > mixed effects model. The model I wand to fit is at an individual level with
> > 4
> > parameters. For all parameters both fixed and random effects have to be
> > estimated, as well as their covariance matrix (see the formula bellow).
> > y~x1+x1^2+x2+x2^2.
> >
> >
> > I tried to fit the model with my data sets, but most of the time, R returns
> > an
> > error message.
> > there are three main types of errors :
> >
> > - In mer_finalize(ans, verbose) :
> >   function evaluation limit reached without convergence (9)
> >
> > -  there are false convergence (8)
> >
> > -there are singular convergence (7)
> >
> > Do you know how to resolve these problems. Is there a way to modify the
> > parameters of the maximization algorithm to avoid these error messages?
> >
> > Thank you for your help and answers.
> >
> > Regards,
> >
> > Yufeng Zhang
> >
> > _______________________________________________
> > R-sig-mixed-models at r-project.org mailing list
> > https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models
> >
>
>
>
> --
> Gillian M Raab
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>