To cite ROI in publications use:

Theu├čl S, Schwendinger F, Hornik K (2020). “ROI: An Extensible R Optimization Infrastructure.” Journal of Statistical Software, 94(15), 1–64. doi: 10.18637/jss.v094.i15.

Corresponding BibTeX entry:

  @Article{,
    title = {{ROI}: An Extensible {R} Optimization Infrastructure},
    author = {Stefan Theu{\ss}l and Florian Schwendinger and Kurt
      Hornik},
    journal = {Journal of Statistical Software},
    year = {2020},
    volume = {94},
    number = {15},
    pages = {1--64},
    doi = {10.18637/jss.v094.i15},
  }