To cite the gren package in publications please use:

Münch, M.M., Peeters, C.F.W., van der Vaart, A.W., and van de Wiel M.A. (2018). Adaptive group-regularized logistic elastic net regression. arXiv:1805.00389v1 [stat.ME].

Corresponding BibTeX entry:

    title = {The Spectral Condition Number Plot for Regularization
      Parameter Determination},
    author = {M.M. Münch and C.F.W. Peeters and A.W. {van der Vaart}
      and M.A. {van de Wiel}},
    journal = {arXiv:1805.00389v1 [stat.ME]},
    year = {2018},