title: gmnl latent class model (R) error "Error in t.default(x) : argument is not a matrix"
body: <p>I try to estimate latent class multinomial logit model from <code>gmnl</code> reference manual examples, it results in error <code>&quot;Error in t.default(x) : argument is not a matrix&quot;</code></p>
  <p>Other models (e.g. &quot;mixl&quot;) work</p>
  <p>R version 4.0.2 (2020-06-22) -- &quot;Taking Off Again&quot;</p>
  <p>Platform: x86_64-w64-mingw32/x64 (64-bit)</p>
  <pre><code>data(&quot;Electricity&quot;, package = &quot;mlogit&quot;)
  
  Electr &lt;- mlogit.data(Electricity, id.var = &quot;id&quot;, choice = &quot;choice&quot;,
  varying = 3:26, shape = &quot;wide&quot;, sep = &quot;&quot;)
  
  Elec.lc &lt;- gmnl(choice ~ pf + cl + loc + wk + tod + seas| 0 | 0 | 0 | 1,
  data = Electr,
  subset = 1:3000,
  model = 'lc',
  panel = TRUE,
  Q = 2)
  
  #Estimating LC model 
  #Error in t.default(x) : argument is not a matrix
  </code></pre>