To cite nlstools in publications use:

Baty F, Ritz C, Charles S, Brutsche M, Flandrois J, Delignette-Muller M (2015). “A Toolbox for Nonlinear Regression in R: The Package nlstools.” Journal of Statistical Software, 66(5), 1–21. doi: 10.18637/jss.v066.i05, https://www.jstatsoft.org/article/view/v066i05.

Corresponding BibTeX entry:

  @Article{,
    title = {A Toolbox for Nonlinear Regression in {R}: The Package
      {nlstools}},
    author = {Florent Baty and Christian Ritz and Sandrine Charles and
      Martin Brutsche and Jean-Pierre Flandrois and Marie-Laure
      Delignette-Muller},
    journal = {Journal of Statistical Software},
    year = {2015},
    volume = {66},
    number = {5},
    pages = {1--21},
    url = {https://www.jstatsoft.org/article/view/v066i05},
    doi = {10.18637/jss.v066.i05},
  }