To cite GrassmannOptim in publications use:

Adragni KP, Cook RD, Wu S (2012). “GrassmannOptim: An R Package for Grassmann Manifold Optimization.” Journal of Statistical Software, 50(5), 1–18. https://www.jstatsoft.org/v50/i05/.

Corresponding BibTeX entry:

  @Article{,
    title = {{GrassmannOptim}: An {R} Package for Grassmann Manifold
      Optimization},
    author = {Kofi P. Adragni and R. Dennis Cook and Seongho Wu},
    journal = {Journal of Statistical Software},
    year = {2012},
    volume = {50},
    number = {5},
    pages = {1--18},
    url = {https://www.jstatsoft.org/v50/i05/},
  }