//  A procedure to be used for testing a Richardson based error estimator.
//  Just return a value corrupted with some errors proportional to various
//   powers of n.        
    
#include <iostream.h>
    
int fakeInt( double *f, double x, int n) {

   if ( n <= 0 ) { // Check for correctness of the input. 
      cout << " Error in fakeInt.  Got n = " << n << endl;
      return 1;} // Print an error message and quit with an error flag. 
      
   *f = (double) 1.234 + x/(n*n) + ((double) 1 )/ (n*n*n) + (x*x)/(n*n*n*n);
   
//  This part adds errors designed to make the error estimator fail.  
//  Comment it out if you want the error estimator to succeed.        
    
   *f += n % 23; // Adding the residual of n mod 23 should give a function
                 // that varies in a seemingly random way as n is decreased,
                 // thus foiling the Richardson estimator.  
   
   return 0;
   
 }

/*  A driver to check fakeInt.   Comment out the whole thing before using. */ 

int main() {

   int n; double x; double f; int errorCode;
   
   n=1000; x=10;
   
          errorCode = 
   fakeInt( &f, x, n); 
   cout << "got f= "<< f << ", x= " << x << ",  errorCode= " << errorCode ;
   cout << ", x = " << x << endl;  
   
   return 0;
   
 }