convergence in polr

Why have you sent a message about S-PLUS to R-help, one that has already 
been answered on S-news?

There is no function nlminb in R.

On 24 Feb 2004, C. Spanou wrote:

Hello splus-users, I am trying to fit a regression model for an 
ordered response factor. So I am using the function polr in 
library(MASS). My data is a matrix of 1665 rows and 63 columns (one of 
the column is the dependent variable). The code I use is 
polr(as.ordered(q23p)~.,data=newdatap)
 but I am getting the following warning message singularity 
encountered in: nlminb.1(temp, p, liv, lv, objective, gradient, bounds, 
scale)

I looked in the MASS help for nlminb and I found that for the function
nlminb(start, objective, gradient=NULL, hessian=NULL,  
       scale=1, control=NULL, lower=-Inf, upper=Inf) 
 

when returning a warning message of singularity means that the 
optimization algorithm thinks it can't make any further progress 
because it has too many degrees of freedom. It usually means that the 
objective function is either not differentiable, or it may not have an 
optimum.

So for my data an optimum can't be obtained.
Is this true?

Can I ignore this warning message since what I want to find is values 
for the boundaries? Will the values for the boundaries be accurate even 
though I get the warning message?