Clarify which MPI_Comm is referred to in a comment

diff --git a/source/base/process_grid.cc b/source/base/process_grid.cc
index f75596fe17d9633cb20d14f17f36486a299fb3b6..dfd36e595556e8ccc5f8eb5b310e3a6ee02ef0b2 100644 (file)
--- a/source/base/process_grid.cc
+++ b/source/base/process_grid.cc
@@ -168,8 +168,10 @@ namespace Utilities
                             &inactive_with_root_group);
       AssertThrowMPI(ierr);
 
-      // Create the communicator based on the group
-      // Note that on most cores the communicator will be MPI_COMM_NULL.
+      // Create the communicator based on inactive_with_root_group.
+      // Note that on all the active MPI processes (except for the one with
+      // rank 0) the resulting MPI_Comm mpi_communicator_inactive_with_root
+      // will be MPI_COMM_NULL.
       ierr = Utilities::MPI::create_group(mpi_communicator, inactive_with_root_group,
                                           55, &mpi_communicator_inactive_with_root);
       AssertThrowMPI(ierr);