To cite ptmixed in publications use:

Signorelli M, Spitali P, Szigyarto CA, Consortium TM, Tsonaka R (2021). “Penalized regression calibration: a method for the prediction of survival outcomes using complex longitudinal and high-dimensional data.” arXiv preprint: arXiv:2101.04426. https://arxiv.org/abs/2101.04426.

Corresponding BibTeX entry:

  @Article{,
    title = {Penalized regression calibration: a method for the
      prediction of survival outcomes using complex longitudinal and
      high-dimensional data},
    author = {M. Signorelli and P. Spitali and C. Al-Khalili Szigyarto
      and The MARK-MD Consortium and R. Tsonaka},
    journal = {arXiv preprint: arXiv:2101.04426},
    year = {2021},
    url = {https://arxiv.org/abs/2101.04426},
  }