fn kambe_downward(
n: i32,
z: Complex,
eta: Complex,
pair: [(Complex, f64); 2],
) -> (Complex, f64)Expand description
The Kambe (1968) recurrence I_n = (n+3) I_(n+2) - z^2 I_(n+4) + eta^(n+3) e^(...)
run downward from the base pair, with the first-order absolute error bound in units
of epsilon propagated from the pair and each endpoint term.