Function uk_money_yield 

pub fn uk_money_yield(real_yield: f64, assumed_inflation: f64) -> f64

The DMO money yield implied by a real yield under assumed annual inflation pi: (1 + y/2) = (1 + ρ/2)·(1 + π)^{1/2}.

At pi = 0 this is the identity — the money and real yields coincide when nothing is projected, which is the check the tests hang on.