Improve error message.

diff --git a/source/multigrid/mg_transfer_matrix_free.cc b/source/multigrid/mg_transfer_matrix_free.cc
index e15f327f0ee3af7f99e3ae2aae564b78b8051537..7d06c3ce9b325e3e4ab15a0ef2310fbdc85e3ac9 100644 (file)
--- a/source/multigrid/mg_transfer_matrix_free.cc
+++ b/source/multigrid/mg_transfer_matrix_free.cc
@@ -101,9 +101,10 @@ MGTransferMatrixFree<dim, Number>::build(
 {
   Assert(dof_handler.has_level_dofs(),
          ExcMessage(
-           "The underlying DoFHandler object did not call "
-           "distribute_mg_dofs(). This is a prerequisite for multigrid "
-           "transfers."));
+           "The underlying DoFHandler object has not had its "
+           "distribute_mg_dofs() function called, but this is a prerequisite "
+           "for multigrid transfers. You will need to call this function, "
+           "probably close to where you already call distribute_dofs()."));
 
   this->fill_and_communicate_copy_indices(dof_handler);
 

diff --git a/source/multigrid/mg_transfer_prebuilt.cc b/source/multigrid/mg_transfer_prebuilt.cc
index 30a6695d9fbbc170ad26c311ce82fd40d18f8b34..e986774fac86b826c71de545c13bdb690769983d 100644 (file)
--- a/source/multigrid/mg_transfer_prebuilt.cc
+++ b/source/multigrid/mg_transfer_prebuilt.cc
@@ -154,9 +154,10 @@ MGTransferPrebuilt<VectorType>::build(
 {
   Assert(dof_handler.has_level_dofs(),
          ExcMessage(
-           "The underlying DoFHandler object did not call "
-           "distribute_mg_dofs(). This is a prerequisite for multigrid "
-           "transfers."));
+           "The underlying DoFHandler object has not had its "
+           "distribute_mg_dofs() function called, but this is a prerequisite "
+           "for multigrid transfers. You will need to call this function, "
+           "probably close to where you already call distribute_dofs()."));
 
   const unsigned int n_levels =
     dof_handler.get_triangulation().n_global_levels();