Stopping criterion based on L2 time residuals

Stopping criterion based on L2 time residuals

This is an example of cs_user_extra_operations allowing to properly stop a computation when the L2 time residuals (displayed in the run_solver.log file) of all solved variables have decreased below a value of 1e-3.

L2 time residuals of a variable at a given time step are a relative measure of the unsteady term of its transport equation:

  /* get total number of fields */
  int n_fields = cs_field_n_fields();

  /* get time step structure */
  cs_time_step_t *ts = cs_get_glob_time_step();

  /* declare a C structure holding solving information values */
  cs_solving_info_t sinfo;

  bool cved = true;

  /* criterion is set here to 1e-3 */
  cs_real_t epsres = 1e-3;

  /* loop over all fields */
  for (int f_id = 0; f_id < n_fields; f_id++) {
    cs_field_t *f = cs_field_by_id(f_id);

    /* filter fields of type variable (i.e. the solved ones) */
    if (f->type & CS_FIELD_VARIABLE) {
      /* get solving info structure for current field */
      cs_field_get_key_struct(f, cs_field_key_id("solving_info"), &sinfo);

      /* has the value of the L2 time residual decreased below criterion ? */
      cved = cved && (sinfo.l2residual  <= epsres);
    }
  }

  /* if current iteration is the second to last one, nothing to do */
  cved = cved && (ts->nt_cur < ts->nt_max);

  /* otherwise if converged */
  if (cved) {
    /* set maximum number of iteration to the next one */
    ts->nt_max = ts->nt_cur+1;

    /* Warning: L2 time residual is computed after extra operations */
    bft_printf("Converged at %d\n",ts->nt_max);
  }