double secant ( double x0, double x1, double f ( double x ) )
{
  int step;
  double fx0, fx1, fx2, x2;
//
//  Initialization.
//
  step = 0;
  fx0 = f ( x0 );
  fx1 = f ( x1 );
//
//  Iteration loop.
//
  while ( true )
  {
    x2 = ( fx1 * x0 - fx0 * x1 ) / ( fx1 - fx0 );
    fx2 = f ( x2 );
    step = step + 1;
//
//  Can we accept the new point?
//
    if ( fabs ( fx2 ) < 0.000001 ) 
    {
      break;
    }
//
//  Quit if we take too many steps!
//
    if ( 25 <= step )
    {
      cerr << "SECANT - Too many steps!\n";
      exit ( 1 );
    }
//
//  Prepare for next step.
//
    x0 = x1;
    fx0 = fx1;
    x1 = x2;
    fx1 = fx2;
  }
  return x2;
}