final SegmentIntegral integrator = new SegmentIntegral(5000);
final double infinity = 10.0*Math.sqrt(variance);
r.value =
process.riskFreeRate().currentLink().discount(a.exercise.lastDate()) /
Math.sqrt(2.0*Math.PI*variance) * integrator.op(f, drift-infinity, drift+infinity);
}
//
// private inner classes