Due to the complexity of deriving a closedfrom solution, the Greeks are evaluated by computing a discrete approximation of the partial derivative. That is, the option is revalued with a fractional change for each relevant parameter (e.g. Spot for Delta, Volatility for Vega, etc) and the change in the option value divided by the increment is the approximated Greek.

OV = option value. OV_{1} = option value derived from using the incremented parameter. S = spot price of the underlying asset. S_{1} = S + I I = an incremental change of 0.00001. r = riskfree interest rate, expressed with continuous compounding. r_{1} = r + I. b = cost of carry for the underlying asset, expressed with continuous compounding. b_{1} = b + I. vol = volatility of the relative price change of the underlying asset. vol_{1}= vol + I. T = time to maturity measured in years (actual/365 basis). T_{1} = T  I. = Delta of OV_{1.} 

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