To cite orca in publications use:

Hočevar T, Demšar J (2016). “Computation of Graphlet Orbits for Nodes and Edges in Sparse Graphs.” Journal of Statistical Software, 71(10), 1–24. doi:10.18637/jss.v071.i10.

Corresponding BibTeX entry:

  @Article{,
    title = {Computation of Graphlet Orbits for Nodes and Edges in
      Sparse Graphs},
    author = {Toma\v{z} Ho\v{c}evar and Janez Dem\v{s}ar},
    journal = {Journal of Statistical Software},
    year = {2016},
    volume = {71},
    number = {10},
    pages = {1--24},
    doi = {10.18637/jss.v071.i10},
  }