Całkowanie numeryczne

#include <iostream>
        #include <cstdlib>

        using namespace std;

        double f(double x) {
                return 3*(x*x)+x;
        }

        double prostokat(double min, double max, int n) {
                double h = ((max - min) / n);
                double suma = 0;

                for (int i = 0; i < n; i++) {
                        double p = h*f(min + i*h);
                        suma += p;
                }
                return suma;
        }

        double trapez(double min, double max, int n) {
                double h = ((max - min) / n);
                double suma = 0;

                for (int i = 0; i < n; i++) {
                        double p = (f(min + i*h)+f(min+i*h+h))*h/2;
                        suma += p;
                }
                return suma;
        }

        double simpson(double min, double max, int n) {
                double suma = 0;
                double h = ((max - min) / n);

                for (int i = 0; i < n; i++) {
                        double f0 = f(min + i*h);
                        double f1 = f(min + i*h+h/2);
                        double f2 = f(min + i*h+h);

                        double p = h / (2 * 3) * (f0 + 4 * f1 + f2);
                        suma += p;
                }
                return suma;
        }

        int main(){

            cout.precision(4);
            cout.setf(ios::fixed);

                double wynik = prostokat(4, 12, 2 );
                cout << wynik <<endl;

                double wynik3 = trapez(4, 12, 2 );
                cout << wynik3 << endl;

                double wyunik2 = simpson(4, 12, 2 );
                cout<<wyunik2<<endl;



                system("pause");
            return 0;
        }