To cite ahaz in publications use:

Anders Gorst-Rasmussen, Thomas H. Scheike (2012). Coordinate Descent Methods for the Penalized Semiparametric Additive Hazards Model. Journal of Statistical Software, 47(9), 1-17. URL http://www.jstatsoft.org/v47/i09/.

Corresponding BibTeX entry:

  @Article{,
    title = {Coordinate Descent Methods for the Penalized
      Semiparametric Additive Hazards Model},
    author = {Anders Gorst-Rasmussen and Thomas H. Scheike},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {47},
    number = {9},
    pages = {1--17},
    url = {http://www.jstatsoft.org/v47/i09/},
  }