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  1. #include <stdio.h>
  2. #include <stdlib.h>
  3. #include <math.h>
  4.  
  5. #define F(t) (5 + 2*(t) + 0.6*(t)*exp(-0.3*(t)*(t)))
  6.  
  7. double binsearch(const double t0, const double r, const double dec) {
  8.   const double eps = pow(10, -dec);
  9.  
  10.   double a = t0 - r;
  11.   double b = t0 + r;
  12.   double c = t0;
  13.  
  14.   do {
  15.     double F_a = F(a);
  16.     double F_b = F(b);
  17.     double F_c = F(c);
  18.  
  19.   	if (fabs(F_c) < eps) {
  20.   	  return c;
  21.   	}
  22.  
  23.     if (signbit(F_a) ^ signbit(F_c)) {
  24.       b = c;
  25.     } else if (signbit(F_c) ^ signbit(F_b)) {
  26.       a = c;
  27.     } else {
  28.       return NAN;
  29.     }
  30.  
  31.     c = (a + b) / 2;
  32.   } while (1);
  33. }
  34.  
  35. main() {
  36.   printf("found: %1.10f\n", binsearch(-2.5, 0.5, 10));
  37.   return 0;
  38. }
Success #stdin #stdout 0s 2008KB
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found: -2.3678784467
https://ideone.com/ZUTfnT
language:
C (gcc 8.3)
created:
8 years ago
visibility:
secret

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