To cite package ‘apt’ in publications use:

  Sun C (2024). _apt: Asymmetric Price Transmission_. R package version
  4.0, <https://CRAN.R-project.org/package=apt>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {apt: Asymmetric Price Transmission},
    author = {Changyou Sun},
    year = {2024},
    note = {R package version 4.0},
    url = {https://CRAN.R-project.org/package=apt},
  }