Make incompatibility more clear

diff --git a/doc/news/changes/incompatibilities/20190603MartinKronbichler b/doc/news/changes/incompatibilities/20190603MartinKronbichler
index 9e6a7def5bdeea09a2a9845854ac39184be6d77d..1f85cdbaf699b86ace63f5214671ec6800566045 100644 (file)
--- a/doc/news/changes/incompatibilities/20190603MartinKronbichler
+++ b/doc/news/changes/incompatibilities/20190603MartinKronbichler
@@ -1,9 +1,11 @@
 Changed: The functions DoFHandler::n_locally_owned_dofs_per_processor(),
 DoFHandler::locally_owned_dofs_per_processor() and
-DoFHandler::locally_owned_mg_dofs_per_processor() previously return a
+DoFHandler::locally_owned_mg_dofs_per_processor() previously returned a
 reference to an internally stored array of index sets on all processors. As
 this cannot scale to large processor counts, these functions have been marked
-deprecated and only populate the internal vectors on the first demand. Use the
+deprecated and only populate the internal vectors on the first demand. This
+means that the first call must be a collective call on all MPI ranks to ensure
+that the underlying MPI_Allgather function completes. Use the
 new functions DoFHandler::compute_n_locally_owned_dofs_per_processor(),
 DoFHandler::compute_locally_owned_dofs_per_processor() and
 DoFHandler::compute_locally_owned_mg_dofs_per_processor() instead or, even