Add to the documentation.

diff --git a/include/deal.II/base/mpi.h b/include/deal.II/base/mpi.h
index c8ba9fad275f23ace5053dc049b046ce777e5f2a..18f98bb3d62db5b7db137800762a31aeb7774af6 100644 (file)
--- a/include/deal.II/base/mpi.h
+++ b/include/deal.II/base/mpi.h
@@ -1471,6 +1471,12 @@ namespace Utilities
      * via MPI functions to another process, and using
      * `mpi_type_id_for_type<decltype(obj)>` to infer the correct MPI type to
      * use for the communication.
+     *
+     * The type `T` given here must be one of the data types supported
+     * by MPI, such as `int` or `double`. It may not be an array of
+     * objects of such a type, or a pointer to an object of such a
+     * type. The compiler will produce an error if this requirement is
+     * not satisfied.
      */
     template <typename T>
     const MPI_Datatype