nc_break_even_yrs: Calculate number of years it takes to break even (if ever)
In southwick-associates/lifetime: Provide functions for lifetime pricing

Description Usage Arguments See Also Examples

Generally it will take some number of years for cumulative revenue in the lifetime scenario to catch up with cumulative revenue in the annual scenario. If the lifetime scenario does catch up, the years to break even represents the number of years it takes for this to happen. Only rows (ages) where the current price is above the break-even price will be returned (otherwise to lifetime return will never reach the annual return scenario).

nc_break_even_yrs(retain_all, prices, return_life, inflation,
  wsfr_amount = NULL, min_amount = NULL, senior_price = NULL,
  youth_ages = 0:15, age_cutoff = 80, fund_years = 0:200,
  senior_age = 65)

`retain_all`	data frame of predicted years by age like that produced by `nc_retain_all`
`prices`	data frame of lifetime prices by age with at least 2 variables: current_age and price_lifetime
`return_life`	percentage return from lifetime fund
`inflation`	inflation rate for depreciation of lifetime fund
`wsfr_amount`	numeric estimated amount for aid dollars (use SFRF for fishing, WRF for hunting)
`min_amount`	numeric the minimum expenditure that will count for a certified hunter/angler (use 2 for hunt/fish and 4 for combo)
`senior_price`	numeric price for a senior lifetime license
`youth_ages`	if not NULL, assumes for youths that the fund is able to compound until adulthood (when the agency will begin drawing revenue). See `nc_price_lifetime_youth` for details.
`age_cutoff`	numeric final age that can be counted for lifetime license-based WSFR dollars
`fund_years`	range of years to cast forward for stream-based lifetime fund valuation
`senior_age`	numeric age when a participant will be expected to buy a cheap lifetime license