Calculates the annual effective interest rate given the nominal rate and number of compounding periods per year.
nominal_rate- The nominal interest rate per year.
periods_per_year- The number of compounding periods per year.
NOMINAL: Calculates the annual nominal interest rate given the effective rate and number of compounding periods per year.
INTRATE: Calculates the effective interest rate generated when an investment is purchased at one price and sold at another with no interest or dividends generated by the investment itself.