Function par_by_linearity 

fn par_by_linearity<R: Scalar, P: Priceable<R>>(
    at_zero: &P,
    at_one: &P,
    view: &PricingView<'_, R>,
    product: &'static str,
) -> Result<R, PricingError>

The root of a value affine in one contract number, from the product struck at 0 and at 1: −V(0) / (V(1) − V(0)).