To cite kohonen in publications use:

  Wehrens R, Kruisselbrink J (2018). “Flexible Self-Organizing Maps in
  kohonen 3.0.” _Journal of Statistical Software_, *87*(7), 1-18.
  doi:10.18637/jss.v087.i07 <https://doi.org/10.18637/jss.v087.i07>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Flexible Self-Organizing Maps in {kohonen} 3.0},
    author = {Ron Wehrens and Johannes Kruisselbrink},
    journal = {Journal of Statistical Software},
    year = {2018},
    volume = {87},
    number = {7},
    pages = {1--18},
    doi = {10.18637/jss.v087.i07},
  }

Wehrens R, Buydens LMC (2007). “Self- and Super-Organizing Maps in R:
The kohonen Package.” _Journal of Statistical Software_, *21*(5), 1-19.
doi:10.18637/jss.v021.i05 <https://doi.org/10.18637/jss.v021.i05>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Self- and Super-Organizing Maps in {R}: The {kohonen} Package},
    author = {Ron Wehrens and Lutgarde M. C. Buydens},
    journal = {Journal of Statistical Software},
    year = {2007},
    volume = {21},
    number = {5},
    pages = {1--19},
    doi = {10.18637/jss.v021.i05},
  }