Calculate implied volatility using the SABR (Stochastic Alpha Beta Rho) model. SABR is the industry standard for modeling volatility smiles in interest rate and FX markets. Returns the Black-equivalent implied volatility for a given strike, forward, and SABR parameters (alpha, beta, rho, nu).
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Forward price of the underlying
x >= 0100
Option strike price
x >= 0102
Time to expiry in years
x >= 01
SABR alpha parameter (overall volatility level)
x >= 00.25
SABR beta parameter (0=normal, 1=lognormal, 0.5=CIR). Controls backbone shape
0 <= x <= 10.5
SABR rho parameter (correlation between forward and volatility). Controls skew
-1 <= x <= 1-0.2
SABR nu parameter (volatility of volatility). Controls smile curvature
x >= 00.3