To cite cgam in publications use:

  Liao X, Meyer MC (2019). “cgam: An R Package for the Constrained
  Generalized Additive Model.” _Journal of Statistical Software_,
  *89*(5), 1-24.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{cgam}: An {R} Package for the Constrained Generalized Additive Model},
    author = {Xiyue Liao and Mary C. Meyer},
    journal = {Journal of Statistical Software},
    year = {2019},
    volume = {89},
    number = {5},
    pages = {1--24},
  }