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

[yufeng at nsm.umass.edu]

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