void PrintResult   // a sample function that outputs on file...
                   // ...some intermediate results

         (int    dim,          // dimension of the solution vector
          double t,            // current time
          double x_ [],        // current solution vector
          FILE*  res)          // pointer to output file

{ 
  int i;

  (void) fprintf (res, "%20.5f", t);

  for (i = 0; i < dim; i++)
    (void) fprintf (res, " %10.7f", x_ [i]);

  (void) fprintf (res, "\n");
}