/*  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 <stdio.h>
    
int fakeInt( double *f, double x, int n) {

   if ( n <= 0 ) { /* Check for correctness of the input. */
      printf(" Error in fakeInt.  Got n = %d\n",n);
      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=100; x=10;
   
          errorCode = 
   fakeInt( &f, x, n); 
   printf("got f= %12.4e, x=%12.4e, errorCode=%4d, n=%8d\n",f,x,errorCode,n);  
   
   return 0;
   
 }