diff_func.cpp

#include <iostream>
#include <cmath>
#include <iomanip>

using namespace std;

inline double f(double x) { return log(x+1)-2*x*x+1;    /* f(x) */ }
inline double df(double x) { return 1/fabs(x+1)-4*x;    /* f'(x) */ }

int main() {
    // left
    int count = 0;
    double x = 2.0, dx = 1.0;
    for (int i = 0; i < 20; ++i, dx *= 0.1) {
        double dy = (f(x) - f(x-dx)) / dx;
        cout << i << ":\t";
        cout << "dx = " << setw(9) << dx << "\t";
        cout << "y'(x0) = " << dy << endl;
    }


    printf("check: %0.9f\n", df(2.0));

    return 0;
}