Please cite ARCokrig including its version number as

  Ma P (2019). “ARCokrig: Autoregressive Cokriging Models for
  Multifidelity Codes.” R package version 0.1.2,
  <https://github.com/pulongma/ARCokrig>.

A BibTeX entry for LaTeX users is

  @Misc{,
    title = {ARCokrig: Autoregressive Cokriging Models for Multifidelity Codes},
    author = {Pulong Ma},
    note = {R package version 0.1.2},
    organization = {Statistical and Applied Mathematical Sciences Institute},
    address = {Durham, NC, USA},
    year = {2019},
    url = {https://github.com/pulongma/ARCokrig},
  }