//-------------------------------------------------------------------------
/// <summary>
/// Calculates the present value sensitivity to the SABR model parameters of the swaption product.
/// <para>
/// The sensitivity of the present value to the SABR model parameters, alpha, beta, rho and nu.
///
/// </para>
/// </summary>
/// <param name="swaption"> the swaption product </param>
/// <param name="ratesProvider"> the rates provider </param>
/// <param name="swaptionVolatilities"> the volatilities </param>
/// <returns> the point sensitivity to the SABR model parameters </returns>
public virtual PointSensitivityBuilder presentValueSensitivityModelParamsSabr(ResolvedSwaption swaption, RatesProvider ratesProvider, SabrSwaptionVolatilities swaptionVolatilities)
{
validate(swaption, ratesProvider, swaptionVolatilities);
double expiry = swaptionVolatilities.relativeTime(swaption.Expiry);
ResolvedSwap underlying = swaption.Underlying;
ResolvedSwapLeg fixedLeg = this.fixedLeg(underlying);
double tenor = swaptionVolatilities.tenor(fixedLeg.StartDate, fixedLeg.EndDate);
double shift = swaptionVolatilities.shift(expiry, tenor);
double strike = calculateStrike(fixedLeg);
if (expiry < 0d)
{ // Option has expired already
return(PointSensitivityBuilder.none());
}
double forward = SwapPricer.parRate(underlying, ratesProvider);
double volatility = swaptionVolatilities.volatility(expiry, tenor, strike, forward);
double numeraire = calculateNumeraire(swaption, fixedLeg, forward, ratesProvider);
DoubleArray derivative = swaptionVolatilities.volatilityAdjoint(expiry, tenor, strike, forward).Derivatives;
double vega = numeraire * swaption.LongShort.sign() * BlackFormulaRepository.vega(forward + shift, strike + shift, expiry, volatility);
// sensitivities
Currency ccy = fixedLeg.Currency;
SwaptionVolatilitiesName name = swaptionVolatilities.Name;
return(PointSensitivityBuilder.of(SwaptionSabrSensitivity.of(name, expiry, tenor, ALPHA, ccy, vega * derivative.get(2)), SwaptionSabrSensitivity.of(name, expiry, tenor, BETA, ccy, vega * derivative.get(3)), SwaptionSabrSensitivity.of(name, expiry, tenor, RHO, ccy, vega * derivative.get(4)), SwaptionSabrSensitivity.of(name, expiry, tenor, NU, ccy, vega * derivative.get(5))));
}