Before revision: During last 15 years various parameterizations of the implied volatility (IV) surface were proposed in the literature to address few goals: a) given market data on some options build a no-arbitrage local volatility (Dupire's) surface to further exploit it for calibration of a local stochastic volatility model; b) obtain volatilities for pricing OTC options and other derivatives with strikes and maturities other than that offered by option exchanges; c) produce a volatility forecast over future periods of time, which is helpful in Value-at-Risk models, computing forward IVs and exposures, etc. , d) assess an adequacy of an option pricing model based on the shape of the IV surface. Among various existing parameterizations SVI model of Gatheral is the most elaborated one which takes into account a correct asymptotic behavior at wings, and respects no-arbitrage conditions as well as no-arbitrage interpolation and extrapolation.
After revision: During last 15 years various parameterizations of the implied volatility surface which is constructed by using polynomials of sigmoid functions combined with some other terms. This parameterization is flexible enough to fit market implied volatilities which demonstrate smile or skew. An arbitrage-free calibration algorithm is considered that constructs the implied volatility surface as a grid in the strike-expiration space and guarantees a lack of arbitrage at every node of this grid. We also demonstrate how to construct an arbitrage-free interpolation and extrapolation in time, as well as build a local volatility and implied pdf surfaces. Asymptotic behavior of this parameterization is discussed, as well as results on stability of the calibrated parameters are presented. Numerical examples show robustness of the proposed approach in building all these surfaces as well as no-arbitrage interpolation and extrapolation.