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  1.  
  2. #include <bits/stdc++.h>
  3. using namespace std;
  4.  
  5. pair<double, double> horner(const vector<double> &a, double x) {
  6.     double p = a[0], dp = 0;
  7.     for (int i = 1; i < (int)a.size(); i++) {
  8.         dp = dp * x + p;
  9.         p = p * x + a[i];
  10.     }
  11.     return {p, dp};
  12. }
  13.  
  14. int main() {
  15.     int n;
  16.     cin >> n;
  17.     vector<double> a(n + 1);
  18.     for (int i = 0; i <= n; i++) cin >> a[i];
  19.  
  20.     double x0;
  21.     cin >> x0;
  22.  
  23.     const double E = 1e-8;
  24.     cout << fixed << setprecision(10);
  25.     cout << "Iter\t" << setw(12) << "x"
  26.          << "\t" << setw(12) << "f(x)"
  27.          << "\t" << setw(12) << "f'(x)"
  28.          << "\t" << setw(12) << "error\n";
  29.  
  30.     for (int i = 1; i <= 100; i++) {
  31.         auto [fx, dfx] = horner(a, x0);
  32.  
  33.         if (fabs(dfx) < 1e-14) {
  34.             cout << "Derivative too small at iteration " << i << ", stopping.\n";
  35.             break;
  36.         }
  37.  
  38.         double x1 = x0 - fx / dfx;
  39.         double error = fabs(x1 - x0);
  40.  
  41.         cout << i << "\t" 
  42.              << setw(12) << x0 << "\t" 
  43.              << setw(12) << fx << "\t" 
  44.              << setw(12) << dfx << "\t" 
  45.              << setw(12) << error << "\n";
  46.  
  47.         if (fabs(x1 - x0) < E * max(1.0, fabs(x1))) {
  48.             cout << "Root = " << x1 << "\n";
  49.             break;
  50.         }
  51.  
  52.         x0 = x1;
  53.     }
  54.  
  55.     return 0;
  56. }
Success #stdin #stdout 0.01s 5320KB
comments (?)
stdin 
2
1 0 -2
1
stdout 
Iter	           x	        f(x)	       f'(x)	      error
1	1.0000000000	-1.0000000000	2.0000000000	0.5000000000
2	1.5000000000	0.2500000000	3.0000000000	0.0833333333
3	1.4166666667	0.0069444444	2.8333333333	0.0024509804
4	1.4142156863	0.0000060073	2.8284313725	0.0000021239
5	1.4142135624	0.0000000000	2.8284271247	0.0000000000
Root = 1.4142135624
https://ideone.com/w1HA36
language:
C++14 (clang 8.0)
created:
8 days ago
visibility:
public

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