title: maximum number of iterations (maxIter = 50) reached without convergence
body: <p>I am using R to conduct non-linear mixed effect model analysis. I have 23 groups data, each group has 5 points, and in my model, there are four parameters. My code is below </p>
  
  <pre><code>&gt; model&lt;-nlme(un~Johnson(Temp,mu0,Ea,dED,Topt),
  fixed=list(mu0~1,Ea~1,dED~1,Topt~1),random=mu0+Ea+dED+Topt~1|id,
  data=dilution2,
  start=c(mu0=1,Ea=0.6,dED=0.5,Topt=20))
  </code></pre>
  
  <p>but it end up with errors<a href="https://i.stack.imgur.com/XeLnS.png" rel="nofollow noreferrer">enter image description here</a></p>
  
  <p>even I set the maxIter by nlmeControl().
  please help me solve this problem. thanks very much.</p>