ABOUT OUTPUT IN PARALLEL

[孙翔]

Hi, all,

I followed step-18 and wrote an HPC code in which I used a set of DOFs to output two variables T and P. I debugged the coed and the code runs well. However, it only outputs one variable, for the other variable, it only outputs the number of processors not the value of the variable. Parts of the code is attached as follows. 

The code looped to get the variables T and P solutions at each time step using the function output_results. The output_resutlts function was almost copied from step-18. I hope the code can output both T and P values, but when I use ParaView to read the files, ParaView only displays the value of P and can not display the other. Could someone help me check the code? Thank you very much.

template <int dim>

void CoupledTH<dim>::run() {

    make_grid();

    setup_system();

    do {

        assemble_P_system();

        linear_solve_P();

        assemble_T_system();

        linear_solve_T();

        time += time_step;

        output_results(T_solution, "T");

        output_results(P_solution, "P");

    } while (time < period);

}

template <int dim>

void CoupledTH<dim>::output_results(Vector<double>& solution,

                                    std::string var_name) const {

  DataOut<dim> data_out;

  data_out.attach_dof_handler(dof_handler);

  data_out.add_data_vector(solution, var_name);

  std::vector<types::subdomain_id> partition_int(

      triangulation.n_active_cells());

  GridTools::get_subdomain_association(triangulation, partition_int);

  const Vector<double> partitioning(partition_int.begin(), partition_int.end());

  data_out.add_data_vector(partitioning, "partitioning");

  data_out.build_patches();

  const std::string filename =

      var_name + "-solution-" + Utilities::int_to_string(timestep_number, 3);

  const std::string pvtu_master_filename = data_out.write_vtu_with_pvtu_record(

      "outputfiles/", filename, timestep_number, mpi_communicator);

  if (this_mpi_process == 0) {

    static std::vector<std::pair<double, std::string>> times_and_names;

    times_and_names.push_back(

        std::pair<double, std::string>(time, pvtu_master_filename));

    std::ofstream pvd_output("outputfiles/"+ var_name + "_solution.pvd");

    DataOutBase::write_pvd_record(pvd_output, times_and_names);

  }

}

[Jean-Paul Pelteret]

Hi,

The problem is most likely that you’ve got on (static) variable “times_and_names” that is referencing two completely different of output files. This means that for every tilmestep, you’ve now got two entries in this file and Paraview probably doesn’t know what to do with it. You can easily check this by commenting out one call to “output_results()” and then the other. You’ll see that solution field because now the formatting of the PVD file is what Paraview expects it to be.

There are at least two solutions to the problem. You either (1) have to move the “ times_and_names” variable out of this function and have one copy for the “P” output files and one for the “T” output files, or (2) simply add both solutions to the same output files. You could achieve this in the following way (assuming that the DoFHandler is common to both fields, which it looks like it must be):

template <int dim>
void CoupledTH<dim>::output_results(const std::vector<std::pair<const Vector<double>*, std::string>>& solutions_and_names) const {
  DataOut<dim> data_out;

  data_out.attach_dof_handler(dof_handler);

  for (auto solution_and_name : solutions_and_names)

  {

    const Vector<double>*solution = solution_and_name.first;
    const std::string var_name = solution_and_name.second;

    data_out.add_data_vector(*solution, var_name);

  }

 ...

}

template <int dim>
void CoupledTH<dim>::run() {

    ...
    do {
        …

        std::vector<std::pair<const Vector<double>*,std::string>> solutions_and_names;

        solutions_and_names.push_back(std::make_pair(&T_solution, "T"));

        solutions_and_names.push_back(std::make_pair(&P_solution, "P"));

        output_results(solutions_and_names );

    } while (time < period);
}

Notice that you probably want to avoid copying the vector, so you probably want to consider using pointers (or a std::reference) if you go this (preferred) route. Its easiest to collect them up as a std::pair, since they are logically bound to one another.

I hope that this helps, either as a real solution to the problem or by giving you a hint as to how you might be able to navigate your way around the problem that you’re seeing.

Best,

Jean-Paul

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[孙翔]

Thank you very much. It works now. 

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