Function loan_oas_with 

pub(crate) fn loan_oas_with<R: Scalar>(
    loan: &CallableLoan,
    view: &PricingView<'_, R>,
    clean_price: f64,
) -> Result<f64, PricingError>

The continuous OAS at which a callable loan’s clean price is clean_price, a passive solve as callable_oas_with’s.