bisect.cpp

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#include "bisect.h"
#include <cassert>
#include <cmath>                  // abs()
#include <functional>             // function; C++11
 
double Bisect(const std::function<double(double)>& func,
              const double a, const double b, const double eps)
{
    assert(func(a)>0 && 0>func(b));
    double c = (a + b) / 2, fc = func(c), x0;
 
    if ( std::abs(fc) < eps ) {
        x0 = c;                 // end of recursion
    }
    else if (  fc > 0.0 ) {
        x0 = Bisect(func, c, b, eps);   // search in right intervall
    }
    else {              // i.e., fc < 0.0
        x0 = Bisect(func, a, c, eps);   // search in left intervall
    }
 
    return x0;                  // return with solution
}