Citing copa may involve the original methodology paper as well as the
software itself. To cite the methodology paper, see e.g, the help page
for the copa function. To cite the software, use the following
citation.

  COPA--cancer outlier profile analysis. Bioinformatics. 2006
  Dec1;22(23):2950--1. Epub 2006 Aug 7.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {COPA - cancer outlier profile analysis.},
    author = {{MacDonald} and {JW} and {Ghosh} and {D.}},
    journal = {Bioinformatics},
    volume = {22(23)},
    year = {2006},
    pages = {2950--1},
  }