Please cite the pks package by the following reference:

Heller, J. and Wickelmaier, F. (2013). Minimum discrepancy estimation in probabilistic knowledge structures. Electronic Notes in Discrete Mathematics, 42, 49-56.

Corresponding BibTeX entry:

  @Article{,
    title = {Minimum discrepancy estimation in probabilistic knowledge
      structures},
    author = {J"urgen Heller and Florian Wickelmaier},
    journal = {Electronic Notes in Discrete Mathematics},
    year = {2013},
    volume = {42},
    pages = {49--56},
  }