To cite PtProcess in publications use:

  Harte, D.S. (2010). PtProcess: An R Package for Modelling Marked
  Point Processes Indexed by Time. Journal of Statistical Software,
  35(8), 1-32. doi: 10.18637/jss.v035.i08

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{PtProcess}: An {R} Package for Modelling Marked Point Processes Indexed by Time},
    author = {David S. Harte},
    journal = {Journal of Statistical Software},
    year = {2010},
    volume = {35},
    number = {8},
    pages = {1--32},
    doi = {10.18637/jss.v035.i08},
    url = {https://cran.r-project.org/package=PtProcess},
  }
