RungeKutta4order

std::vector<double> rungekutta4order(const std::function<double(double)> &f, const MethodParams &params) {
    int n = (int) ((params.x1 - params.x0) / params.h) + 1;
    std::vector<double> solution;
    double ynext;
    double yi = params.y0;
    double xi = params.x0;
    double h = params.h;
    solution.push_back(yi);

    for (int i = 1; i < n; i++) {
        double k1 = h * f(yi);
        double k2 = h * f(yi + 0.5 * k1);
        double k3 = h * f(yi + 0.5 * k2);
        double k4 = h * f(yi + k3);

        ynext = yi + (1.0 / 6.0) * (k1 + 2 * k2 + 2 * k3 + k4);
        solution.push_back(ynext);
        xi += params.x0 + i * params.h;
        yi = ynext;
    }

    return solution;
}