To cite bgw estimation algorithms in publications use:

Bunch D, Gay D, Welsch R (1993). “Algorithm 717-Subroutines for maximum likelihood and quasi-likelihood estimation of parameters in nonlinear regression models.” ACM Transactions on Mathematical Software, 19(1), 21. doi:10.1145/151271.151279, https://dl.acm.org/doi/10.1145/151271.151279.

Corresponding BibTeX entry:

  @Article{,
    title = {Algorithm 717-Subroutines for maximum likelihood and
      quasi-likelihood estimation of parameters in nonlinear regression
      models},
    author = {David S. Bunch and David M. Gay and Roy E. Welsch},
    journal = {ACM Transactions on Mathematical Software},
    year = {1993},
    volume = {19},
    number = {1},
    pages = {21},
    doi = {10.1145/151271.151279},
    url = {https://dl.acm.org/doi/10.1145/151271.151279},
  }