Merge pull request #14900 from peterrum/feeval_docu

Different documentation updates in `matrix_free`

diff --cc include/deal.II/matrix_free/fe_evaluation.h
index 70a5e20955463c3dae4f7192bccbd07852cbf683,3a9245ce561a8278bed5ffc3583d080ef1b3d9fc..e08b6b7b08f54b4a9a0cb9828444aab013ae6d2a
--- 1/include/deal.II/matrix_free/fe_evaluation.h
--- 2/include/deal.II/matrix_free/fe_evaluation.h
+++ b/include/deal.II/matrix_free/fe_evaluation.h
@@@ -474,9 -474,9 +474,9 @@@ public
  
    /**
     * Return the divergence of a vector-valued finite element at quadrature
 -   * point number @p q_point after a call to @p evaluate(...,true,...).
 +   * point number @p q_point after a call to @p evaluate(EvaluationFlags::gradients).
     *
-    * @note Only available for n_components_==dim.
+    * @note Only available for the vector-valued case (n_components == dim).
     */
    VectorizedArrayType
    get_divergence(const unsigned int q_point) const;
@@@ -484,19 -484,19 +484,19 @@@
    /**
     * Return the symmetric gradient of a vector-valued finite element at
     * quadrature point number @p q_point after a call to @p
 -   * evaluate(...,true,...). It corresponds to <tt>0.5
 +   * evaluate(EvaluationFlags::gradients). It corresponds to <tt>0.5
     * (grad+grad<sup>T</sup>)</tt>.
     *
-    * @note Only available for n_components_==dim.
+    * @note Only available for the vector-valued case (n_components == dim).
     */
    SymmetricTensor<2, dim, VectorizedArrayType>
    get_symmetric_gradient(const unsigned int q_point) const;
  
    /**
     * Return the curl of the vector field, $\nabla \times v$ after a call to @p
 -   * evaluate(...,true,...).
 +   * evaluate(EvaluationFlags::gradients).
     *
-    * @note Only available for n_components_==dim.
+    * @note Only available for the vector-valued case (n_components == dim).
     */
    Tensor<1, (dim == 2 ? 1 : dim), VectorizedArrayType>
    get_curl(const unsigned int q_point) const;