To cite nlstools in publications use:

Florent Baty, Christian Ritz, Sandrine Charles, Martin Brutsche, Jean-Pierre Flandrois, Marie-Laure Delignette-Muller (2015). A Toolbox for Nonlinear Regression in R: The Package nlstools. Journal of Statistical Software, 66(5), 1-21. URL http://www.jstatsoft.org/v66/i05/.

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 = {http://www.jstatsoft.org/v66/i05/},
  }