To cite in publications use:

  Matzke N, Sidje R, Schmidt D (2023). _rexpokit v0.26.6.13: R wrappers
  for EXPOKIT; other matrix functions_. School of Biological Sciences,
  University of Auckland, New Zealand. NOTE 1: Additional URLs:
  https://zenodo.org/badge/latestdoi/17001945 ,
  http://dx.doi.org/10.5281/zenodo.1442889 ,
  https://cran.r-project.org/package=rexpokit ,
  http://phylo.wikidot.com/rexpokit.
  
  NOTE 2: The EXPOKIT FORTRAN library was published in: Sidje, R.B.
  (1998). A Software Package for Computing Matrix Exponentials.
  ACM-Transactions on Mathematical Software, 24(1):130-156.
  http://tinyurl.com/bwa87rq ;
  
  Also, the rexpokit R package was first published in: Matzke, Nicholas
  J. (2013). Probabilistic historical biogeography: new models for
  founder-event speciation, imperfect detection, and fossils allow
  improved accuracy and model-testing. Frontiers of Biogeography, 5(4),
  242-248.  http://escholarship.org/uc/item/44j7n141,
  <http://phylo.wikidot.com/rexpokit>.

A BibTeX entry for LaTeX users is

  @Manual{,
    title = {rexpokit v0.26.6.13: R wrappers for EXPOKIT; other matrix functions},
    author = {Nicholas J. Matzke and Roger B. Sidje and Drew Schmidt},
    organization = {School of Biological Sciences, University of Auckland},
    address = {New Zealand},
    year = {2023},
    note = {NOTE 1: Additional URLs: https://zenodo.org/badge/latestdoi/17001945 , http://dx.doi.org/10.5281/zenodo.1442889 , https://cran.r-project.org/package=rexpokit , http://phylo.wikidot.com/rexpokit. 

NOTE 2: The EXPOKIT FORTRAN library was published in: Sidje, 
R.B. (1998). A Software Package for Computing Matrix Exponentials. 
ACM-Transactions on Mathematical Software, 24(1):130-156. 
http://tinyurl.com/bwa87rq ; 

Also, the rexpokit R package was first published in: 
Matzke, Nicholas J. (2013). Probabilistic historical biogeography: 
      new models for founder-event speciation, imperfect detection, and fossils allow 
      improved accuracy and model-testing. Frontiers of Biogeography, 5(4), 242-248. 
      http://escholarship.org/uc/item/44j7n141},
    url = {http://phylo.wikidot.com/rexpokit},
  }

A lot of time and effort in creating EXPOKIT and rexpokit, please cite
it, Sidje (1998), and Matzke (2013) when using it for publication. See
also ‘citation("pkgname")’ for citing R packages.