@FUNCTION=OPT_BJER_STENS
@SYNTAX=OPT_BJER_STENS(call_put_flag,spot,strike,time,rate,volatility[,cost_of_carry])
@DESCRIPTION=OPT_BJER_STENS models the theoretical price of american options according to the Bjerksund & Stensland approximation technique.
@call_put_flag is 'c' or 'p' to indicate whether the option is a call or a put.
@spot is the spot price of the underlying asset.
@strike is the strike price at which the option is struck.
@time is the number of days to maturity of the option.
@rate is the annualized risk-free rate of interest.
@volatility is the annualized volatility in price of the underlying asset.
@cost_of_carry is the leakage in value of the underlying asset, for common stocks, this would be the dividend yield.
@EXAMPLES=
@SEEALSO=OPT_BS, OPT_BS_DELTA, OPT_BS_RHO, OPT_BS_THETA, OPT_BS_GAMMA