To cite KRLS in publications use:

Ferwerda J, Hainmueller J, Hazlett CJ (2017). “Kernel-Based Regularized Least Squares in R (KRLS) and Stata (krls).” Journal of Statistical Software, 79(3), 1–26. doi:10.18637/jss.v079.i03.

Corresponding BibTeX entry:

  @Article{,
    title = {Kernel-Based Regularized Least Squares in {R} ({KRLS}) and
      {Stata} ({krls})},
    author = {Jeremy Ferwerda and Jens Hainmueller and Chad J.
      Hazlett},
    journal = {Journal of Statistical Software},
    year = {2017},
    volume = {79},
    number = {3},
    pages = {1--26},
    doi = {10.18637/jss.v079.i03},
  }