To cite package ‘dde’ in publications use:

  FitzJohn R, Hinsley W (2024). _dde: Solve Delay Differential
  Equations_. R package version 1.0.7,
  <https://github.com/mrc-ide/dde>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {dde: Solve Delay Differential Equations},
    author = {Rich FitzJohn and Wes Hinsley},
    year = {2024},
    note = {R package version 1.0.7},
    url = {https://github.com/mrc-ide/dde},
  }