double MonteCarloRule::calculate(double xStart, double xEnd, int quantity) {
    std::default_random_engine generator;
    std::uniform_real_distribution<double> distribution(xStart, xEnd);
    double sum{0};
    for (int i = 0; i < quantity; ++i) {
        sum += Function::value(distribution(generator));
    }
    return sum/quantity;
}
//----------------------------------------------------------------------------
double TrapezoidalRule::calculate(double xStart, double xEnd, int quantity) {
    double sum, dx;

    sum = 0;
    dx = (xEnd - xStart) / quantity;

    for (int i = 1; i < quantity; ++i) {
        sum += Function::value(xStart + i * dx);
    }
    sum = (sum + (Function::value(xStart)+Function::value(xEnd)/2))*dx;
    return sum;
}