fn gamma_ratio(v: f64, order: i32, skip: Option<i32>) -> Scaled
Γ(ν + μ + 1)/Γ(ν - μ + 1) = ∏_{i=1}^{μ} (ν + i)(ν + 1 - i); with skip = Some(i) the factor ν + 1 - i of that pair is left out.
Γ(ν + μ + 1)/Γ(ν - μ + 1) = ∏_{i=1}^{μ} (ν + i)(ν + 1 - i)
skip = Some(i)
ν + 1 - i