For large ρ, with ℓ and η fixed,
Reported 2019-01-29 by Gergő Nemes
Reported 2018-05-15 by Ian Thompson
where θℓ(η,ρ) is defined by (33.2.9),
and a and b are defined by (33.8.3).
An equivalent formulation is given by
f0=1, g0=0, f^0=0, g^0=1-(η/ρ),
and for k=0,1,2,…,