message: add mapping if not building mpi
diff: @@ -1892,6 +1892,35 @@ private:
  } // namespace gko
  +#else
  +
  +
  +struct MPI_Comm {};
  +
  +
  +constexpr MPI_Comm MPI_COMM_WORLD{};
  +
  +
  +namespace gko {
  +namespace mpi {
  +
  +/**
  + * Maps each MPI rank to a single device id in a round robin manner.
  + * @param comm used to determine the node-local rank, if no suitable
  + * environment variable is available.
  + * @param num_devices the number of devices per node.
  + * @return device id that this rank should use.
  + */
  +int map_rank_to_device_id(MPI_Comm comm, const int num_devices)
  +{
  + return num_devices;
  +}
  +
  +
  +} // namespace mpi
  +} // namespace gko
  +
  +
  #endif // GKO_HAVE_MPI
  