Fix docu

diff --git a/include/deal.II/multigrid/mg_transfer_global_coarsening.h b/include/deal.II/multigrid/mg_transfer_global_coarsening.h
index fe87c32ebc46bc21477c3e59ee58f989bdc0b53f..ac69a751b77da97aff285bf7e3ac71e1272c996f 100644 (file)
--- a/include/deal.II/multigrid/mg_transfer_global_coarsening.h
+++ b/include/deal.II/multigrid/mg_transfer_global_coarsening.h
@@ -144,8 +144,9 @@ class MGTwoLevelTransfer<dim, LinearAlgebra::distributed::Vector<Number>>
 {
 public:
   /**
-   * Set up global coarsening transfer @p transfer between the given
-   * dof-handlers.
+   * Set up global coarsening between the given DoFHandler objects (
+   * @p dof_handler_fine and @p dof_handler_coarse). The transfer
+   * can be only performed on active levels.
    */
   void
   reinit_geometric_transfer(const DoFHandler<dim> &          dof_handler_fine,
@@ -154,8 +155,10 @@ public:
                             const AffineConstraints<Number> &constraint_coarse);
 
   /**
-   * Set up polynomial coarsening transfer @p transfer between the given
-   * dof-handlers.
+   * Set up polynomial coarsening between the given DoFHandler objects (
+   * @p dof_handler_fine and @p dof_handler_coarse). Polynomial transfers
+   * can be only performed on active levels (`numbers::invalid_unsigned_int`)
+   * or on coarse-grid levels.
    *
    * @note The function polynomial_transfer_supported() can be used to
    *   check if the given polynomial coarsening strategy is supported.