To cite optM in publications use:

Fitak RR (2021). “OptM: estimating the optimal number of migration edges on population trees using Treemix.” Biology Methods and Protocols, 6(1), bpab017. doi: 10.1093/biomethods/bpab017.

Corresponding BibTeX entry:

  @Article{,
    title = {OptM: estimating the optimal number of migration edges on
      population trees using Treemix},
    author = {Robert R. Fitak},
    journal = {Biology Methods and Protocols},
    year = {2021},
    volume = {6},
    number = {1},
    pages = {bpab017},
    doi = {10.1093/biomethods/bpab017},
  }