To cite ManifoldOptim/ROPTLIB in publications use:

Martin S, Raim AM, Huang W, Adragni KP (2020). “ManifoldOptim: An R Interface to the ROPTLIB Library for Riemannian Manifold Optimization.” Journal of Statistical Software, 93(1), 1–32. doi: 10.18637/jss.v093.i01.

Corresponding BibTeX entry:

  @Article{,
    title = {{ManifoldOptim}: An {R} Interface to the {ROPTLIB} Library
      for Riemannian Manifold Optimization},
    author = {Sean Martin and Andrew M. Raim and Wen Huang and Kofi P.
      Adragni},
    journal = {Journal of Statistical Software},
    year = {2020},
    volume = {93},
    number = {1},
    pages = {1--32},
    doi = {10.18637/jss.v093.i01},
  }