To cite package 'fastcluster' in publications use:

Daniel Müllner, fastcluster: Fast hierarchical clustering routines for R and Python, Version 1.1.9, 2013. Available at CRAN http://cran.r-project.org and PyPI http://pypi.python.org/pypi/fastcluster.

Corresponding BibTeX entry:

  @Manual{,
    title = {fastcluster: Fast hierarchical clustering routines for R
      and Python},
    author = {Daniel M\"ullner},
    year = {2013},
    note = {Version 1.1.9},
    url = {http://math.stanford.edu/~muellner},
  }