@FUNCTION=OPT_BS_RHO
@SYNTAX=OPT_BS_RHO(call_put_flag,spot,strike,time,rate,volatility[,cost_of_carry])
@DESCRIPTION=OPT_BS_RHO uses the Black-Scholes model to calculate the 'rho' of a European option with call_put_flag, @call_put_flag struck at @strike on an asset with spot price @spot.
@call_put_flag is 'c' or 'p' to indicate whether the option is a call or a put.
(The rho of an option is the rate of change of its price with respect to the risk free interest rate.)
@time is the time to maturity of the option expressed in years.
@rate is the risk-free interest rate to the exercise date, in percent.
@cost_of_carry is the leakage in value of the underlying asset, for common stocks, this would be the dividend yield.
* The returned value will be expressed as the rate of change of option value, per 100% change in @rate.
@EXAMPLES=
@SEEALSO=OPT_BS, OPT_BS_DELTA, OPT_BS_THETA, OPT_BS_VEGA, OPT_BS_GAMMA