[R] likelyhood maximization problem with polr

[blackscorpio]

Ok, thanks a lot ! I tried to compute the inverse of the variance covariance
matrix of the estimators with vcov, which gave me this error :

>require(MASS) 
>data(iris) 
>model=polr(Species~Sepal.Length+Sepal.Width+Petal.Length+Petal.Width,iris,start
= rep(1, 6),method= "logistic") 
>require(stats)
>vcov(model)

Re-fitting to get Hessian

Erreur dans optim(s0, fmin, gmin, method = "BFGS", hessian = Hess, ...) : 
  la valeur initiale dans 'vmin' n'est pas finie
  
which means " Error in optim(...) : the initial value in 'vmin' is not
finite" ...
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