title: R: Error with polr(): initial value in 'vmmin' is not finite
body: <p>I'm trying to estimate an ordered probit model using polr:
  polr(Rating ~ Currac + Debt + Inflation + GDPpc + GDPgr + Ratio + Levelofdev
  + Eurozone + Default, method ="probit")</p>
  
  <p>where Rating is an ordered discrete dependent variable and the independent
  variables are a set of economic determinants (e.g. inflation rate).</p>
  
  <p>However, I keep getting the same error:</p>
  
  <p><em>Error in optim(s0, fmin, gmin, method = "BFGS", ...) : 
  initial value in 'vmmin' is not finite</em></p>
  
  <p>I found it in the C code (src/main/optim.c), at line 523 in the procedure
  vmmin. An error is thrown because the result of function fminfn is not
  finite. In this function fminfn, at line 82, the result is calculated as
  result = REAL(s)[0]/(OS->fnscale). This does not make much sense to me,
  however.</p>
  
  <p>I understood it should have something to do with a function evaluating at an
  infinite value at the starting values. I was hoping someone could explain
  this in more detail, or help me overcome the problem.</p>
  
  <p>Exluding/omitting NA-values from the dataset does not resolve the problem.
  However, when I delete <strong>either</strong> Inflation or GDPpc from the set of
  regressors, it suddenly works fine. And when I delete everything else but
  keep both Inflation and GDPpc, it also still works. </p>
  
  <p>If you have experienced the same problem or might know how to deal with
  this, I would be really grateful for your response.</p>
  
  <p>Thanks a lot,</p>
  
  <p>Wouter</p>