To cite multipanelfigure in publications use:

  Graumann J, Cotton R (2018). “multipanelfigure: Simple Assembly of
  Multiple Plots and Images into a Compound Figure.” _Journal of
  Statistical Software, Code Snippets_, *84*(3), 1-10.
  doi:10.18637/jss.v084.c03 <https://doi.org/10.18637/jss.v084.c03>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{multipanelfigure}: Simple Assembly of Multiple Plots and Images into a Compound Figure},
    author = {Johannes Graumann and Richard Cotton},
    journal = {Journal of Statistical Software, Code Snippets},
    year = {2018},
    volume = {84},
    number = {3},
    pages = {1--10},
    doi = {10.18637/jss.v084.c03},
  }