Examples

The following C example illustrates how the get the maximum value of a grid function.

  int vindex;             /* grid variable index */
  CCTK_REAL result;       /* resulting reduction value */
  int target_proc;        /* processor to hold the result */
  int reduction_handle;   /* handle for reduction operator */
  char *reduction_name;   /* reduction operator to use */


  /* want to get the maximum for the wavetoy grid function */
  reduction_name = "maximum";
  vindex = CCTK_VarIndex ("wavetoy::phi");

  /* the reduction result will be obtained by processor 0 only */
  target_proc = 0;

  /* get the handle for the given reduction operator */
  reduction_handle = CCTK_ReductionHandle (reduction_name);
  if (reduction_handle >= 0)
  {
    /* now do the reduction using the flesh's generic reduction API
      (passing in one input, expecting one output value of REAL type) */
    if (CCTK_Reduce (cctkGH, target_proc, reduction_handle,
                     1, CCTK_VARIABLE_REAL, &result, 1, vindex) == 0)
    {
      if (CCTK_MyProc (cctkGH) == target_proc)
      {
        printf ("%s reduction value is %f\n", reduction_name, result);
      }
    }
    else
    {
      CCTK_VWarn (1, __LINE__, __FILE__, CCTK_THORNSTRING,
                  "%s reduction failed", reduction_name);
    }
  }
  else
  {
    CCTK_VWarn (1, __LINE__, __FILE__, CCTK_THORNSTRING,
                "Invalid reduction operator '%s'", reduction_name);
  }