eqad

eqad(
    base_value,
    base_year,
    future_value,
    future_year,
    period_of_analysis,
    discount_rate,
)

Equivalent annual damage (EqAD) annualization (interpolate, present-value, PVIFA).

The HEC-FDA annualization math alone: linearly interpolate EAD between the base and most likely future year, hold it flat to the end of the period of analysis, discount each year to present value, and divide by the annuity factor (PVIFA). Wraps the ported Alternative::ComputeEqad. The shared C++ validator requires a period of at least two, a future year later than the base year, and an inclusive base-to-future span no longer than the period.