/*    ATK IV - Numerical Programming (2006)      */
/*      Excercise 6.1 -  Bisection Method        */

#include<stdio.h>
#include<math.h>

float bisect(float x1, float x2, float acc);
float f(float x);

int main(void){

  float x;
  float x1=1.0;
  float x2=2.0;
  float acc=1.0e-5;

  x=bisect(x1,x2,acc);

  printf("%f\n",x);

  return 0;
}

float bisect(float x1, float x2, float acc){
  float z1=x1;
  float z2=x2;
  float f1=f(x1);
  float f2=f(x2);

  float zm,fm;  

  while(fabs(z2-z1)>acc){
    zm=0.5*(z1+z2);
    fm=f(zm);
    if(f1*fm < 0.0){
      z2=zm;
      f2=fm;
    }
    else{
      z1=zm;
      f1=fm;
    }
  }

  return zm;
}

float f(float x){ return exp(x)-5.0;}