Exploring issues about computing special mathematical functions as accurately and efficiently as possibly, including Bessel functions, incomplete Gamma and Beta.
Several R packages providing (algorithms to compute) special mathematical functions, typically all related to computing probability distribution functions, often "DPQ" (Density (pdf), Probability (cdf), and Quantiles (inverse cdf)).
Initiated and currently solely maintained by Martin Maechler, ETH Zurich, and member of the R Core team since primordial times.
Traditionally, I have worked a lot in making the DPQ-functions in (base) R more accurate in border cases, notably implementing the log=TRUE/FALSE and lower.tail = T|F possibilities.
The project summary page you can find here.