/**
* Copyright (C) 2009 - present by OpenGamma Inc. and the OpenGamma group of companies
*
* Please see distribution for license.
*/
package com.opengamma.analytics.financial.model.volatility.smile.function;
import org.apache.commons.lang.NotImplementedException;
import org.apache.commons.lang.Validate;
import com.opengamma.analytics.financial.model.option.pricing.analytic.formula.BlackFunctionData;
import com.opengamma.analytics.financial.model.option.pricing.analytic.formula.CEVFunctionData;
import com.opengamma.analytics.financial.model.option.pricing.analytic.formula.CEVPriceFunction;
import com.opengamma.analytics.financial.model.option.pricing.analytic.formula.EuropeanVanillaOption;
import com.opengamma.analytics.financial.model.volatility.BlackImpliedVolatilityFormula;
import com.opengamma.analytics.math.function.Function1D;
import com.opengamma.util.CompareUtils;
/**
* From the paper Johnson & Nonas, Arbitrage-free construction of the swaption cube (2009). <b>Note:</b> truncation weight does not seem to work
*/
public class SABRJohnsonVolatilityFunction extends VolatilityFunctionProvider<SABRFormulaData> {
private static final double EPS = 1e-15;
private static final CEVPriceFunction CEV_FUNCTION = new CEVPriceFunction();
private static final BlackImpliedVolatilityFormula BLACK_IMPLIED_VOL = new BlackImpliedVolatilityFormula();
@Override
public Function1D<SABRFormulaData, Double> getVolatilityFunction(final EuropeanVanillaOption option, final double forward) {
Validate.notNull(option, "option");
final double k = option.getStrike();
final double t = option.getTimeToExpiry();
final Function1D<CEVFunctionData, Double> priceFunction = CEV_FUNCTION.getPriceFunction(option);
return new Function1D<SABRFormulaData, Double>() {
@SuppressWarnings("synthetic-access")
@Override
public final Double evaluate(final SABRFormulaData data) {
Validate.notNull(data, "data");
final double alpha = data.getAlpha();
final double beta = data.getBeta();
final double rho = data.getRho();
final double nu = data.getNu();
if (CompareUtils.closeEquals(nu, 0, EPS)) {
if (CompareUtils.closeEquals(beta, 1.0, EPS)) {
return alpha; // this is just log-normal
}
throw new NotImplementedException("Have not implemented the case where nu = 0, beta != 0");
}
if (beta > 0) {
final double sigmaDD = alpha * beta * Math.pow(forward, beta - 1);
final double eta = (1 - beta) / beta * forward;
double sigmaBlend;
if (CompareUtils.closeEquals(forward, k, EPS)) {
sigmaBlend = sigmaDD;
} else {
final double z = nu / sigmaDD * Math.log((forward + eta) / (k + eta));
final double sigmaBBF = sigmaDD * z / Math.log((z - rho + Math.sqrt(1 - 2 * rho * z + z * z)) / (1 - rho));
final double sigmaTrunc = sigmaDD * Math.pow(1 - 4 * rho * z + (4.0 / 3.0 + 5 * rho * rho) * z * z, 1.0 / 8.0);
final double w = Math.min(1.0, 1.0 / nu / Math.sqrt(t));
sigmaBlend = 1.0 / (w / sigmaBBF + (1 - w) / sigmaTrunc);
}
sigmaBlend *= 1 + (rho * nu * sigmaDD / 4 + (2 - 3 * rho * rho) * nu * nu / 24) * t;
final double sigmaCEV = sigmaBlend * Math.pow(forward, 1 - beta) / beta;
final CEVFunctionData cevData = new CEVFunctionData(forward, 1, sigmaCEV, beta);
final double price = priceFunction.evaluate(cevData);
return BLACK_IMPLIED_VOL.getImpliedVolatility(new BlackFunctionData(forward, 1, sigmaCEV), option, price);
}
throw new NotImplementedException("Have not implemented the case where b <= 0");
}
};
}
@Override
public int hashCode() {
return toString().hashCode();
}
@Override
public boolean equals(final Object obj) {
if (obj == null) {
return false;
}
if (this == obj) {
return true;
}
if (getClass() != obj.getClass()) {
return false;
}
return true;
}
@Override
public String toString() {
return "SABR (Johnson)";
}
}