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  1. #include <stdio.h>
  2. #include <math.h>
  3.  
  4. #define EPS 1e-5
  5.  
  6. // Function
  7. double f(double x) {
  8.     return x*x - 1 - sin(x);
  9. }
  10.  
  11. // Bisection Method (二分法)
  12. double bisection(double a, double b, int *iterations) {
  13.     double mid;
  14.     *iterations = 0;
  15.  
  16.     while (1) {
  17.         (*iterations)++;
  18.         mid = (a + b) / 2.0;
  19.  
  20.         if (fabs(f(mid)) < EPS) return mid;
  21.  
  22.         if (f(a) * f(mid) < 0)
  23.             b = mid;
  24.         else
  25.             a = mid;
  26.     }
  27. }
  28.  
  29. // False Position Method (はさみうち法)
  30. double false_position(double a, double b, int *iterations) {
  31.     double x;
  32.     *iterations = 0;
  33.  
  34.     while (1) {
  35.         (*iterations)++;
  36.         x = (a * f(b) - b * f(a)) / (f(b) - f(a));
  37.  
  38.         if (fabs(f(x)) < EPS) return x;
  39.  
  40.         if (f(a) * f(x) < 0)
  41.             b = x;
  42.         else
  43.             a = x;
  44.     }
  45. }
  46.  
  47. int main() {
  48.     double r1, r2;
  49.     int it1, it2;
  50.  
  51.     printf("========================================\n");
  52.     printf(" Solving f(x) = x^2 - 1 - sin(x) = 0\n");
  53.     printf("========================================\n");
  54.  
  55.     // ---- Bisection ----
  56.     printf("\n[ Bisection Method ]\n");
  57.  
  58.     r1 = bisection(-1.0, 0.0, &it1);
  59.     printf("Interval [-1,0]: Root = %.6f, Iterations = %d\n", r1, it1);
  60.  
  61.     r2 = bisection(1.0, 2.0, &it2);
  62.     printf("Interval [1,2]: Root = %.6f, Iterations = %d\n", r2, it2);
  63.  
  64.     // ---- False Position ----
  65.     printf("\n[ False Position Method ]\n");
  66.  
  67.     r1 = false_position(-1.0, 0.0, &it1);
  68.     printf("Interval [-1,0]: Root = %.6f, Iterations = %d\n", r1, it1);
  69.  
  70.     r2 = false_position(1.0, 2.0, &it2);
  71.     printf("Interval [1,2]: Root = %.6f, Iterations = %d\n", r2, it2);
  72.  
  73.     return 0;
  74. }
Success #stdin #stdout 0s 5284KB
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========================================
 Solving f(x) = x^2 - 1 - sin(x) = 0
========================================

[ Bisection Method ]
Interval [-1,0]: Root = -0.636734, Iterations = 16
Interval [1,2]: Root = 1.409622, Iterations = 16

[ False Position Method ]
Interval [-1,0]: Root = -0.636732, Iterations = 6
Interval [1,2]: Root = 1.409622, Iterations = 9
https://ideone.com/vMo2el
language:
C (gcc 8.3)
created:
1 day ago
visibility:
public

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