To cite invest in publications use:

Greenwell BM (2013). investr: Functions for Inverse Estimation with Linear and Nonlinear Regression Models in R.. R package version 1.0.1, https://github.com/w108bmg/investr.

Corresponding BibTeX entry:

  @Manual{investr-package,
    title = {investr: Functions for Inverse Estimation with Linear and
      Nonlinear Regression Models in R.},
    author = {Brandon M. Greenwell},
    year = {2013},
    note = {R package version 1.0.1},
    url = {https://github.com/w108bmg/investr},
  }