The package provides a parallel versions of the L-BFGS-B optim method. If the evaluation of the function fn takes more than 0.1 seconds, optimParallel can significantly reduce the optimization time. For a p-parameter optimization, the speed increase is about factor 1+2p when no analytic gradient is specified and 1+2p processor cores are available.
See the R Journal article https://doi.org/10.32614/RJ-2019-030 for more information. It is also available as vignette.
R> vignette("optimParallel")