Comment on <= comparison for MatrixFree::ElementType.

diff --git a/include/deal.II/matrix_free/shape_info.h b/include/deal.II/matrix_free/shape_info.h
index 9533c9c94d4cc3e9d8a5cdc3c1ea8f25803fb846..89c1f2902d0f84927e684486544912edc76eac43 100644 (file)
--- a/include/deal.II/matrix_free/shape_info.h
+++ b/include/deal.II/matrix_free/shape_info.h
@@ -36,6 +36,15 @@ namespace internal
      * initialization. FEEvaluation will select the most efficient algorithm
      * based on the given element type.
      *
+     * There is an implied ordering in the type ElementType::tensor_symmetric
+     * in the sense that both ElementType::tensor_symmetric_collocation and
+     * ElementType::tensor_symmetric_hermite are also of type
+     * ElementType::tensor_symmetric. Likewise, a configuration of type
+     * ElementType::tensor_symmetric is also of type
+     * ElementType::tensor_general. As a consequence, we support `<=`
+     * operations between the types with this sorting, but not against the
+     * even higher indexed types such as ElementType::truncated_tensor.
+     *
      * @ingroup matrixfree
      */
     enum ElementType