To cite simest in publications use:

Arun Kumar Kuchibhotla and Rohit Kumar Patra (2017). simest: Single Index Model Estimation with Constraints on Link Function R package version 0.4. URL https://CRAN.R-project.org/package=simest

Corresponding BibTeX entry:

  @Manual{,
    title = {{simest}: Single Index Model Estimation with Constraints
      on Link Function},
    author = {Arun Kumar Kuchibhotla and Rohit Kumar Patra},
    year = {2017},
    note = {R package version 0.4},
    url = {https://CRAN.R-project.org/package=simest},
  }