To cite package hopach in publications use:

  M.J. van der Laan, K.S. Pollard (2003). Hybrid clustering of gene
  expression data with visualization and the bootstrap. Journal of
  Statistical Planning and Inference, 117: 275-303.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Hybrid clustering of gene expression data with visualization and the bootstrap},
    journal = {Journal of Statistical Planning and Infererence},
    volume = {117},
    pages = {275-303},
    year = {2003},
    author = {Mark J. {van der Laan} and Katherine S. Pollard},
  }