private double GetFirstDerivativeToStrike(double t, double k)
{
double forwardPrice = PriceBump.BumpForward(k);
double backwardPrice = PriceBump.BumpBackward(k);
return((ImpliedVol.GetValue(t, forwardPrice) - ImpliedVol.GetValue(t, backwardPrice)) / (forwardPrice - backwardPrice));
}
