To cite package 'ptw' in publications use:

Bloemberg, T. G. et al. (2010) "Improved Parametric Time Warping for Proteomics", Chemometrics and Intelligent Laboratory Systems, 104 (1), 65-74

Corresponding BibTeX entry:

    title = {Improved Parametric Time Warping for Proteomics},
    author = {Tom G. Bloemberg and Jan Gerretzen and Hans J. P. Wouters
      and Jolein Gloerich and Maurice van Dael and Hans J. C. T.
      Wessels and Lambert P. van den Heuvel and Paul H. C. Eilers and
      Lutgarde M. C. Buydens and Ron Wehrens},
    year = {2010},
    journal = {Chemometrics and Intelligent Laboratory Systems},
    volume = {104},
    number = {1},
    pages = {65-74},