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 the function
nlminb(start, objective, gradient=NULL, hessian=NULL,
scale=1, control=NULL, lower=-Inf, upper=Inf)
returns 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?
Thank you
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