Add documentation about shape function ordering

diff --git a/include/deal.II/fe/fe_dgq.h b/include/deal.II/fe/fe_dgq.h
index ca99e86c0e4f2058094e10615b65c71b36b29e06..acf320c6c5f5662ae6f85ba3d6fa29ef00a0feeb 100644 (file)
--- a/include/deal.II/fe/fe_dgq.h
+++ b/include/deal.II/fe/fe_dgq.h
@@ -435,8 +435,14 @@ public:
 /**
  * Implementation of scalar, discontinuous tensor product elements based on
  * Legendre polynomials, described by the tensor product of the polynomial
- * space Polynomials::Legendre. As opposed to the basic FE_DGQ element, these
- * elements are not interpolatory and no support points are defined.
+ * space Polynomials::Legendre. The tensor product is achieved using
+ * TensorProductPolynomials and the ordering of shape functions, like in
+ * TensorProductPolynomials, is lexicographic. For instance, the ordering in 2d
+ * is $P_0(x)P_0(y),\ P_1(x)P_0(y),\ \ldots,\ P_n(x)P_0(y),\ P_0(x)P_1(y),\ 
+ * \ldots,\ P_n(x)P_1(y),\ \ldots,\ P_0(x)P_n(y),\ \ldots,\ P_n(x)P_n(y)$ when
+ * <tt>degree=n</tt> where $\{P_i\}_{i=0}^{n}$ are the one-dimensional Lagrange
+ * polynomials defined on $[0,1]$. As opposed to the basic FE_DGQ element,
+ * these elements are not interpolatory and no support points are defined.
  *
  * See the base class documentation in FE_DGQ for details.
  */