I accidentally noticed that the descriptions of MathMore functions that use GSL (sometimes) do not define domains of functions.
An example is the ROOT::Math::sph_bessel(unsigned n, double x). It directly uses the gsl_sf_bessel_jl function but nothing is said that one needs … “x >= 0” (well, “n >= 0” is guaranteed because it’s “unsigned”).
Actually, the same problem appears for the ROOT::Math::sph_neumann (unsigned n, double x). It uses the gsl_sf_bessel_yl … and one needs … “x > 0” (what’s worse … this is not even described in the original gsl_sf_bessel_yl description).