To cite multipanelfigure in publications use:

Graumann J and Cotton R (2018). “multipanelfigure: Simple Assembly of Multiple Plots and Images into a Compound Figure.” Journal of Statistical Software, Code Snippets, 84(3), pp. 1–10. doi: 10.18637/jss.v084.c03.

Corresponding BibTeX entry:

  @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},
  }