/// <summary>
/// Test consistency between price methods, and Greek via finite difference.
/// </summary>
public virtual void test_trinomialTree()
{
int nSteps = 135;
double dt = TIME / nSteps;
LatticeSpecification lattice = new CoxRossRubinsteinLatticeSpecification();
double fdEps = 1.0e-4;
foreach (bool isCall in new bool[] { true, false })
{
foreach (double strike in STRIKES)
{
foreach (double interest in INTERESTS)
{
foreach (double vol in VOLS)
{
foreach (double dividend in DIVIDENDS)
{
OptionFunction function = EuropeanVanillaOptionFunction.of(strike, TIME, PutCall.ofPut(!isCall), nSteps);
double[] @params = lattice.getParametersTrinomial(vol, interest - dividend, dt).toArray();
DoubleArray time = DoubleArray.of(nSteps + 1, i => dt * i);
DoubleArray df = DoubleArray.of(nSteps, i => Math.Exp(-interest * dt));
double[][] stateValue = new double[nSteps + 1][];
stateValue[0] = new double[] { SPOT };
IList <DoubleMatrix> prob = new List <DoubleMatrix>();
double[] probs = new double[] { @params[5], @params[4], @params[3] };
for (int i = 0; i < nSteps; ++i)
{
int index = i;
stateValue[i + 1] = DoubleArray.of(2 * i + 3, j => SPOT * Math.Pow(@params[2], index + 1 - j) * Math.Pow(@params[1], j)).toArray();
double[][] probMatrix = new double[2 * i + 1][];
Arrays.fill(probMatrix, probs);
prob.Add(DoubleMatrix.ofUnsafe(probMatrix));
}
RecombiningTrinomialTreeData treeData = RecombiningTrinomialTreeData.of(DoubleMatrix.ofUnsafe(stateValue), prob, df, time);
double priceData = TRINOMIAL_TREE.optionPrice(function, treeData);
double priceParams = TRINOMIAL_TREE.optionPrice(function, lattice, SPOT, vol, interest, dividend);
assertEquals(priceData, priceParams);
ValueDerivatives priceDeriv = TRINOMIAL_TREE.optionPriceAdjoint(function, treeData);
assertEquals(priceDeriv.Value, priceData);
double priceUp = TRINOMIAL_TREE.optionPrice(function, lattice, SPOT + fdEps, vol, interest, dividend);
double priceDw = TRINOMIAL_TREE.optionPrice(function, lattice, SPOT - fdEps, vol, interest, dividend);
double fdDelta = 0.5 * (priceUp - priceDw) / fdEps;
assertEquals(priceDeriv.getDerivative(0), fdDelta, 3.0e-2);
}
}
}
}
}
}
//-----------------------------------------------------------------------
private Pair <ImmutableList <double[]>, RecombiningTrinomialTreeData> calibrate(System.Func <DoublesPair, double> impliedVolatilitySurface, double spot, System.Func <double, double> interestRate, System.Func <double, double> dividendRate)
{
double[][] stateValue = new double[nSteps + 1][];
double[] df = new double[nSteps];
double[] timePrim = new double[nSteps + 1];
IList <DoubleMatrix> probability = new List <DoubleMatrix>(nSteps);
int nTotal = (nSteps - 1) * (nSteps - 1) + 1;
double[] timeRes = new double[nTotal];
double[] spotRes = new double[nTotal];
double[] volRes = new double[nTotal];
// uniform grid based on TrigeorgisLatticeSpecification
double volatility = impliedVolatilitySurface(DoublesPair.of(maxTime, spot));
double dt = maxTime / nSteps;
double dx = volatility * Math.Sqrt(3d * dt);
double upFactor = Math.Exp(dx);
double downFactor = Math.Exp(-dx);
double[] adSec = new double[2 * nSteps + 1];
double[] assetPrice = new double[2 * nSteps + 1];
for (int i = nSteps; i > -1; --i)
{
timePrim[i] = dt * i;
if (i == 0)
{
resolveFirstLayer(interestRate, dividendRate, nTotal, dt, spot, adSec, assetPrice, timeRes, spotRes, volRes, df, stateValue, probability);
}
else
{
double zeroRate = interestRate(timePrim[i]);
double zeroDividendRate = dividendRate(timePrim[i]);
double zeroCostRate = zeroRate - zeroDividendRate;
int nNodes = 2 * i + 1;
double[] assetPriceLocal = new double[nNodes];
double[] callOptionPrice = new double[nNodes];
double[] putOptionPrice = new double[nNodes];
int position = i - 1;
double assetTmp = spot * Math.Pow(upFactor, i);
// call options for upper half nodes
for (int j = nNodes - 1; j > position - 1; --j)
{
assetPriceLocal[j] = assetTmp;
double impliedVol = impliedVolatilitySurface(DoublesPair.of(timePrim[i], assetPriceLocal[j]));
callOptionPrice[j] = BlackScholesFormulaRepository.price(spot, assetPriceLocal[j], timePrim[i], impliedVol, zeroRate, zeroCostRate, true);
assetTmp *= downFactor;
}
// put options for lower half nodes
assetTmp = spot * Math.Pow(downFactor, i);
for (int j = 0; j < position + 2; ++j)
{
assetPriceLocal[j] = assetTmp;
double impliedVol = impliedVolatilitySurface(DoublesPair.of(timePrim[i], assetPriceLocal[j]));
putOptionPrice[j] = BlackScholesFormulaRepository.price(spot, assetPriceLocal[j], timePrim[i], impliedVol, zeroRate, zeroCostRate, false);
assetTmp *= upFactor;
}
resolveLayer(interestRate, dividendRate, i, nTotal, position, dt, zeroRate, zeroDividendRate, callOptionPrice, putOptionPrice, adSec, assetPrice, assetPriceLocal, timeRes, spotRes, volRes, df, stateValue, probability);
}
}
ImmutableList <double[]> localVolData = ImmutableList.of(timeRes, spotRes, volRes);
RecombiningTrinomialTreeData treeData = RecombiningTrinomialTreeData.of(DoubleMatrix.ofUnsafe(stateValue), probability, DoubleArray.ofUnsafe(df), DoubleArray.ofUnsafe(timePrim));
return(Pair.of(localVolData, treeData));
}