QLNet.Vasicek.A C# (CSharp) Метод

        protected override double A(double t, double T)
        {
            double _a = a();
            if (_a < Math.Sqrt(Const.QL_Epsilon))
            {
                return 0.0;
            } else {
                double sigma2 = sigma()*sigma();
                double bt = B(t, T);
                return Math.Exp((b() + lambda()*sigma()/_a
                                 - 0.5*sigma2/(_a*_a))*(bt - (T - t))
                                 - 0.25*sigma2*bt*bt/_a);
            }
        }