OPT_FORWARD_START(call_put_flag,spot,alpha,time_start,time,rate,volatility,cost_of_carry)
call_put_flag: 'c' for a call and 'p' for a put
spot: spot price
alpha: fraction setting the strike price at the future date time_start
time_start: time until the option starts in days
time: time to maturity in days
rate: annualized risk-free interest rate
volatility: annualized volatility of the asset
cost_of_carry: net cost of holding the underlying asset
OPT_BS, OPT_BS_DELTA, OPT_BS_RHO, OPT_BS_THETA, OPT_BS_GAMMA.