public double MethodSplains(double h)
{
double sum1 = 0;
double sum2 = 0;
List <Point> points = new List <Point>();
for (double i = a; i < b; i += h)
{
points.Add(new Point(i, GetFunctionValue(i)));
}
Derivative derivative = new Derivative(points);
for (double i = a; i <= b; i += h)
{
if (i == b)
{
break;
}
sum1 += (GetFunctionValue(i) + GetFunctionValue(i + h)) * h;
sum2 += derivative.CubicInterpolationMethod(3).DerivativePoints.IndexOf(new Point(i, GetFunctionValue(i + h))) * Math.Pow(h, 3);
}
sum1 *= 0.5;
sum2 *= 1 / 12;
double result = sum1 - sum2;
return(result);
}