# Weibull MLE: what is the method/algorithm used to perform the optimization?

Regarding fitting a Weibull two parameters probability density function (pdf), with the fitdistr from MASS package, in R:

1 - What is the iteration algorithm/method used for scale and shape Maximum Likelihood Estimation (MLE)?

I used to think it was Newton-Raphson, but after looking here and here I got confused.

There are Nelder–Mead, quasi-Newton and conjugate-gradient algorithms, but I am not sure which one is used for the iteration process on Weibull 2 parameters pdf MLE.

2 - Based on the answer to question 1, what would be a good reference to study the method?