Method reduce

cpp/dolfinx/common/Table.cpp:69–198

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}
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Table Table::reduce(MPI_Comm comm, Table::Reduction reduction) const
{
  std::string new_title;

  // Prepare reduction operation y := op(y, x)
  std::function<double(double, double)> op_impl;
  switch (reduction)
  {
  case Table::Reduction::average:
    new_title = "[MPI_AVG] ";
    op_impl = [](double y, double x) { return y + x; };
    break;
  case Table::Reduction::min:
    new_title = "[MPI_MIN] ";
    op_impl = [](double y, double x) { return std::min(y, x); };
    break;
  case Table::Reduction::max:
    new_title = "[MPI_MAX] ";
    op_impl = [](double y, double x) { return std::max(y, x); };
    break;
  default:
    throw std::runtime_error("Cannot perform reduction of Table. Requested "
                             "reduction not implemented");
  }
  new_title += name;

  const int mpi_size = dolfinx::MPI::size(comm);

  // Handle trivial reduction
  if (mpi_size == 1)
  {
    Table table_all(*this);
    table_all.name = new_title;
    return table_all;
  }

  // Get keys, values into containers for int doubles
  std::string keys;
  std::vector<double> values;
  for (auto& it : _values)
  {
    if (const auto* const pval = std::get_if<double>(&it.second))
    {
      keys += it.first.first + '\0' + it.first.second + '\0';
      values.push_back(*pval);
    }
  }

  // Gather to rank zero

  // Get string data size on each process
  std::vector<int> pcounts(mpi_size), offsets(mpi_size + 1, 0);
  const int local_size_str = keys.size();
  int err = MPI_Gather(&local_size_str, 1, MPI_INT, pcounts.data(), 1, MPI_INT,
                       0, comm);
  dolfinx::MPI::check_error(comm, err);
  std::partial_sum(pcounts.begin(), pcounts.end(), offsets.begin() + 1);
  std::vector<char> out_str(offsets.back());